// SPDX-License-Identifier: GPL-2.0
/*
 * linux/drivers/staging/erofs/unzip_vle.c
 *
 * Copyright (C) 2018 HUAWEI, Inc.
 *             http://www.huawei.com/
 * Created by Gao Xiang <gaoxiang25@huawei.com>
 *
 * This file is subject to the terms and conditions of the GNU General Public
 * License.  See the file COPYING in the main directory of the Linux
 * distribution for more details.
 */
#include "unzip_vle.h"
#include "compress.h"
#include <linux/prefetch.h>

#include <trace/events/erofs.h>

/*
 * a compressed_pages[] placeholder in order to avoid
 * being filled with file pages for in-place decompression.
 */
#define PAGE_UNALLOCATED     ((void *)0x5F0E4B1D)

/* how to allocate cached pages for a workgroup */
enum z_erofs_cache_alloctype {
        DONTALLOC,      /* don't allocate any cached pages */
        DELAYEDALLOC,   /* delayed allocation (at the time of submitting io) */
};

/*
 * tagged pointer with 1-bit tag for all compressed pages
 * tag 0 - the page is just found with an extra page reference
 */
typedef tagptr1_t compressed_page_t;

#define tag_compressed_page_justfound(page) \
        tagptr_fold(compressed_page_t, page, 1)

static struct workqueue_struct *z_erofs_workqueue __read_mostly;
static struct kmem_cache *z_erofs_workgroup_cachep __read_mostly;

void z_erofs_exit_zip_subsystem(void)
{
        destroy_workqueue(z_erofs_workqueue);
        kmem_cache_destroy(z_erofs_workgroup_cachep);
}

static inline int init_unzip_workqueue(void)
{
        const unsigned int onlinecpus = num_possible_cpus();

        /*
         * we don't need too many threads, limiting threads
         * could improve scheduling performance.
         */
        z_erofs_workqueue =
                alloc_workqueue("erofs_unzipd",
                                WQ_UNBOUND | WQ_HIGHPRI | WQ_CPU_INTENSIVE,
                                onlinecpus + onlinecpus / 4);

        return z_erofs_workqueue ? 0 : -ENOMEM;
}

static void init_once(void *ptr)
{
        struct z_erofs_vle_workgroup *grp = ptr;
        struct z_erofs_vle_work *const work =
                z_erofs_vle_grab_primary_work(grp);
        unsigned int i;

        mutex_init(&work->lock);
        work->nr_pages = 0;
        work->vcnt = 0;
        for (i = 0; i < Z_EROFS_CLUSTER_MAX_PAGES; ++i)
                grp->compressed_pages[i] = NULL;
}

static void init_always(struct z_erofs_vle_workgroup *grp)
{
        struct z_erofs_vle_work *const work =
                z_erofs_vle_grab_primary_work(grp);

        atomic_set(&grp->obj.refcount, 1);
        grp->flags = 0;

        DBG_BUGON(work->nr_pages);
        DBG_BUGON(work->vcnt);
}

int __init z_erofs_init_zip_subsystem(void)
{
        z_erofs_workgroup_cachep =
                kmem_cache_create("erofs_compress",
                                  Z_EROFS_WORKGROUP_SIZE, 0,
                                  SLAB_RECLAIM_ACCOUNT, init_once);

        if (z_erofs_workgroup_cachep) {
                if (!init_unzip_workqueue())
                        return 0;

                kmem_cache_destroy(z_erofs_workgroup_cachep);
        }
        return -ENOMEM;
}

enum z_erofs_vle_work_role {
        Z_EROFS_VLE_WORK_SECONDARY,
        Z_EROFS_VLE_WORK_PRIMARY,
        /*
         * The current work was the tail of an exist chain, and the previous
         * processed chained works are all decided to be hooked up to it.
         * A new chain should be created for the remaining unprocessed works,
         * therefore different from Z_EROFS_VLE_WORK_PRIMARY_FOLLOWED,
         * the next work cannot reuse the whole page in the following scenario:
         *  ________________________________________________________________
         * |      tail (partial) page     |       head (partial) page       |
         * |  (belongs to the next work)  |  (belongs to the current work)  |
         * |_______PRIMARY_FOLLOWED_______|________PRIMARY_HOOKED___________|
         */
        Z_EROFS_VLE_WORK_PRIMARY_HOOKED,
        /*
         * The current work has been linked with the processed chained works,
         * and could be also linked with the potential remaining works, which
         * means if the processing page is the tail partial page of the work,
         * the current work can safely use the whole page (since the next work
         * is under control) for in-place decompression, as illustrated below:
         *  ________________________________________________________________
         * |  tail (partial) page  |          head (partial) page           |
         * | (of the current work) |         (of the previous work)         |
         * |  PRIMARY_FOLLOWED or  |                                        |
         * |_____PRIMARY_HOOKED____|____________PRIMARY_FOLLOWED____________|
         *
         * [  (*) the above page can be used for the current work itself.  ]
         */
        Z_EROFS_VLE_WORK_PRIMARY_FOLLOWED,
        Z_EROFS_VLE_WORK_MAX
};

struct z_erofs_vle_work_builder {
        enum z_erofs_vle_work_role role;
        /*
         * 'hosted = false' means that the current workgroup doesn't belong to
         * the owned chained workgroups. In the other words, it is none of our
         * business to submit this workgroup.
         */
        bool hosted;

        struct z_erofs_vle_workgroup *grp;
        struct z_erofs_vle_work *work;
        struct z_erofs_pagevec_ctor vector;

        /* pages used for reading the compressed data */
        struct page **compressed_pages;
        unsigned int compressed_deficit;
};

#define VLE_WORK_BUILDER_INIT() \
        { .work = NULL, .role = Z_EROFS_VLE_WORK_PRIMARY_FOLLOWED }

#ifdef EROFS_FS_HAS_MANAGED_CACHE
static void preload_compressed_pages(struct z_erofs_vle_work_builder *bl,
                                     struct address_space *mc,
                                     pgoff_t index,
                                     unsigned int clusterpages,
                                     enum z_erofs_cache_alloctype type,
                                     struct list_head *pagepool,
                                     gfp_t gfp)
{
        struct page **const pages = bl->compressed_pages;
        const unsigned int remaining = bl->compressed_deficit;
        bool standalone = true;
        unsigned int i, j = 0;

        if (bl->role < Z_EROFS_VLE_WORK_PRIMARY_FOLLOWED)
                return;

        gfp = mapping_gfp_constraint(mc, gfp) & ~__GFP_RECLAIM;

        index += clusterpages - remaining;

        for (i = 0; i < remaining; ++i) {
                struct page *page;
                compressed_page_t t;

                /* the compressed page was loaded before */
                if (READ_ONCE(pages[i]))
                        continue;

                page = find_get_page(mc, index + i);

                if (page) {
                        t = tag_compressed_page_justfound(page);
                } else if (type == DELAYEDALLOC) {
                        t = tagptr_init(compressed_page_t, PAGE_UNALLOCATED);
                } else {        /* DONTALLOC */
                        if (standalone)
                                j = i;
                        standalone = false;
                        continue;
                }

                if (!cmpxchg_relaxed(&pages[i], NULL, tagptr_cast_ptr(t)))
                        continue;

                if (page)
                        put_page(page);
        }
        bl->compressed_pages += j;
        bl->compressed_deficit = remaining - j;

        if (standalone)
                bl->role = Z_EROFS_VLE_WORK_PRIMARY;
}

/* called by erofs_shrinker to get rid of all compressed_pages */
int erofs_try_to_free_all_cached_pages(struct erofs_sb_info *sbi,
                                       struct erofs_workgroup *egrp)
{
        struct z_erofs_vle_workgroup *const grp =
                container_of(egrp, struct z_erofs_vle_workgroup, obj);
        struct address_space *const mapping = MNGD_MAPPING(sbi);
        const int clusterpages = erofs_clusterpages(sbi);
        int i;

        /*
         * refcount of workgroup is now freezed as 1,
         * therefore no need to worry about available decompression users.
         */
        for (i = 0; i < clusterpages; ++i) {
                struct page *page = grp->compressed_pages[i];

                if (!page || page->mapping != mapping)
                        continue;

                /* block other users from reclaiming or migrating the page */
                if (!trylock_page(page))
                        return -EBUSY;

                /* barrier is implied in the following 'unlock_page' */
                WRITE_ONCE(grp->compressed_pages[i], NULL);

                set_page_private(page, 0);
                ClearPagePrivate(page);

                unlock_page(page);
                put_page(page);
        }
        return 0;
}

int erofs_try_to_free_cached_page(struct address_space *mapping,
                                  struct page *page)
{
        struct erofs_sb_info *const sbi = EROFS_SB(mapping->host->i_sb);
        const unsigned int clusterpages = erofs_clusterpages(sbi);
        struct z_erofs_vle_workgroup *const grp = (void *)page_private(page);
        int ret = 0;    /* 0 - busy */

        if (erofs_workgroup_try_to_freeze(&grp->obj, 1)) {
                unsigned int i;

                for (i = 0; i < clusterpages; ++i) {
                        if (grp->compressed_pages[i] == page) {
                                WRITE_ONCE(grp->compressed_pages[i], NULL);
                                ret = 1;
                                break;
                        }
                }
                erofs_workgroup_unfreeze(&grp->obj, 1);

                if (ret) {
                        ClearPagePrivate(page);
                        put_page(page);
                }
        }
        return ret;
}
#else
static void preload_compressed_pages(struct z_erofs_vle_work_builder *bl,
                                     struct address_space *mc,
                                     pgoff_t index,
                                     unsigned int clusterpages,
                                     enum z_erofs_cache_alloctype type,
                                     struct list_head *pagepool,
                                     gfp_t gfp)
{
        /* nowhere to load compressed pages from */
}
#endif

/* page_type must be Z_EROFS_PAGE_TYPE_EXCLUSIVE */
static inline bool try_to_reuse_as_compressed_page(
        struct z_erofs_vle_work_builder *b,
        struct page *page)
{
        while (b->compressed_deficit) {
                --b->compressed_deficit;
                if (!cmpxchg(b->compressed_pages++, NULL, page))
                        return true;
        }

        return false;
}

/* callers must be with work->lock held */
static int z_erofs_vle_work_add_page(
        struct z_erofs_vle_work_builder *builder,
        struct page *page,
        enum z_erofs_page_type type)
{
        int ret;
        bool occupied;

        /* give priority for the compressed data storage */
        if (builder->role >= Z_EROFS_VLE_WORK_PRIMARY &&
            type == Z_EROFS_PAGE_TYPE_EXCLUSIVE &&
            try_to_reuse_as_compressed_page(builder, page))
                return 0;

        ret = z_erofs_pagevec_ctor_enqueue(&builder->vector,
                                           page, type, &occupied);
        builder->work->vcnt += (unsigned int)ret;

        return ret ? 0 : -EAGAIN;
}

static enum z_erofs_vle_work_role
try_to_claim_workgroup(struct z_erofs_vle_workgroup *grp,
                       z_erofs_vle_owned_workgrp_t *owned_head,
                       bool *hosted)
{
        DBG_BUGON(*hosted);

        /* let's claim these following types of workgroup */
retry:
        if (grp->next == Z_EROFS_VLE_WORKGRP_NIL) {
                /* type 1, nil workgroup */
                if (cmpxchg(&grp->next, Z_EROFS_VLE_WORKGRP_NIL,
                            *owned_head) != Z_EROFS_VLE_WORKGRP_NIL)
                        goto retry;

                *owned_head = &grp->next;
                *hosted = true;
                /* lucky, I am the followee :) */
                return Z_EROFS_VLE_WORK_PRIMARY_FOLLOWED;

        } else if (grp->next == Z_EROFS_VLE_WORKGRP_TAIL) {
                /*
                 * type 2, link to the end of a existing open chain,
                 * be careful that its submission itself is governed
                 * by the original owned chain.
                 */
                if (cmpxchg(&grp->next, Z_EROFS_VLE_WORKGRP_TAIL,
                            *owned_head) != Z_EROFS_VLE_WORKGRP_TAIL)
                        goto retry;
                *owned_head = Z_EROFS_VLE_WORKGRP_TAIL;
                return Z_EROFS_VLE_WORK_PRIMARY_HOOKED;
        }

        return Z_EROFS_VLE_WORK_PRIMARY; /* :( better luck next time */
}

struct z_erofs_vle_work_finder {
        struct super_block *sb;
        pgoff_t idx;
        unsigned int pageofs;

        struct z_erofs_vle_workgroup **grp_ret;
        enum z_erofs_vle_work_role *role;
        z_erofs_vle_owned_workgrp_t *owned_head;
        bool *hosted;
};

static struct z_erofs_vle_work *
z_erofs_vle_work_lookup(const struct z_erofs_vle_work_finder *f)
{
        bool tag, primary;
        struct erofs_workgroup *egrp;
        struct z_erofs_vle_workgroup *grp;
        struct z_erofs_vle_work *work;

        egrp = erofs_find_workgroup(f->sb, f->idx, &tag);
        if (!egrp) {
                *f->grp_ret = NULL;
                return NULL;
        }

        grp = container_of(egrp, struct z_erofs_vle_workgroup, obj);
        *f->grp_ret = grp;

        work = z_erofs_vle_grab_work(grp, f->pageofs);
        /* if multiref is disabled, `primary' is always true */
        primary = true;

        DBG_BUGON(work->pageofs != f->pageofs);

        /*
         * lock must be taken first to avoid grp->next == NIL between
         * claiming workgroup and adding pages:
         *                        grp->next != NIL
         *   grp->next = NIL
         *   mutex_unlock_all
         *                        mutex_lock(&work->lock)
         *                        add all pages to pagevec
         *
         * [correct locking case 1]:
         *   mutex_lock(grp->work[a])
         *   ...
         *   mutex_lock(grp->work[b])     mutex_lock(grp->work[c])
         *   ...                          *role = SECONDARY
         *                                add all pages to pagevec
         *                                ...
         *                                mutex_unlock(grp->work[c])
         *   mutex_lock(grp->work[c])
         *   ...
         *   grp->next = NIL
         *   mutex_unlock_all
         *
         * [correct locking case 2]:
         *   mutex_lock(grp->work[b])
         *   ...
         *   mutex_lock(grp->work[a])
         *   ...
         *   mutex_lock(grp->work[c])
         *   ...
         *   grp->next = NIL
         *   mutex_unlock_all
         *                                mutex_lock(grp->work[a])
         *                                *role = PRIMARY_OWNER
         *                                add all pages to pagevec
         *                                ...
         */
        mutex_lock(&work->lock);

        *f->hosted = false;
        if (!primary)
                *f->role = Z_EROFS_VLE_WORK_SECONDARY;
        else    /* claim the workgroup if possible */
                *f->role = try_to_claim_workgroup(grp, f->owned_head,
                                                  f->hosted);
        return work;
}

static struct z_erofs_vle_work *
z_erofs_vle_work_register(const struct z_erofs_vle_work_finder *f,
                          struct erofs_map_blocks *map)
{
        bool gnew = false;
        struct z_erofs_vle_workgroup *grp = *f->grp_ret;
        struct z_erofs_vle_work *work;

        /* if multiref is disabled, grp should never be nullptr */
        if (unlikely(grp)) {
                DBG_BUGON(1);
                return ERR_PTR(-EINVAL);
        }

        /* no available workgroup, let's allocate one */
        grp = kmem_cache_alloc(z_erofs_workgroup_cachep, GFP_NOFS);
        if (unlikely(!grp))
                return ERR_PTR(-ENOMEM);

        init_always(grp);
        grp->obj.index = f->idx;
        grp->llen = map->m_llen;

        z_erofs_vle_set_workgrp_fmt(grp, (map->m_flags & EROFS_MAP_ZIPPED) ?
                                    Z_EROFS_VLE_WORKGRP_FMT_LZ4 :
                                    Z_EROFS_VLE_WORKGRP_FMT_PLAIN);

        if (map->m_flags & EROFS_MAP_FULL_MAPPED)
                grp->flags |= Z_EROFS_VLE_WORKGRP_FULL_LENGTH;

        /* new workgrps have been claimed as type 1 */
        WRITE_ONCE(grp->next, *f->owned_head);
        /* primary and followed work for all new workgrps */
        *f->role = Z_EROFS_VLE_WORK_PRIMARY_FOLLOWED;
        /* it should be submitted by ourselves */
        *f->hosted = true;

        gnew = true;
        work = z_erofs_vle_grab_primary_work(grp);
        work->pageofs = f->pageofs;

        /*
         * lock all primary followed works before visible to others
         * and mutex_trylock *never* fails for a new workgroup.
         */
        mutex_trylock(&work->lock);

        if (gnew) {
                int err = erofs_register_workgroup(f->sb, &grp->obj, 0);

                if (err) {
                        mutex_unlock(&work->lock);
                        kmem_cache_free(z_erofs_workgroup_cachep, grp);
                        return ERR_PTR(-EAGAIN);
                }
        }

        *f->owned_head = &grp->next;
        *f->grp_ret = grp;
        return work;
}

#define builder_is_hooked(builder) \
        ((builder)->role >= Z_EROFS_VLE_WORK_PRIMARY_HOOKED)

#define builder_is_followed(builder) \
        ((builder)->role >= Z_EROFS_VLE_WORK_PRIMARY_FOLLOWED)

static int z_erofs_vle_work_iter_begin(struct z_erofs_vle_work_builder *builder,
                                       struct super_block *sb,
                                       struct erofs_map_blocks *map,
                                       z_erofs_vle_owned_workgrp_t *owned_head)
{
        const unsigned int clusterpages = erofs_clusterpages(EROFS_SB(sb));
        struct z_erofs_vle_workgroup *grp;
        const struct z_erofs_vle_work_finder finder = {
                .sb = sb,
                .idx = erofs_blknr(map->m_pa),
                .pageofs = map->m_la & ~PAGE_MASK,
                .grp_ret = &grp,
                .role = &builder->role,
                .owned_head = owned_head,
                .hosted = &builder->hosted
        };
        struct z_erofs_vle_work *work;

        DBG_BUGON(builder->work);

        /* must be Z_EROFS_WORK_TAIL or the next chained work */
        DBG_BUGON(*owned_head == Z_EROFS_VLE_WORKGRP_NIL);
        DBG_BUGON(*owned_head == Z_EROFS_VLE_WORKGRP_TAIL_CLOSED);

        DBG_BUGON(erofs_blkoff(map->m_pa));

repeat:
        work = z_erofs_vle_work_lookup(&finder);
        if (work) {
                unsigned int orig_llen;

                /* increase workgroup `llen' if needed */
                while ((orig_llen = READ_ONCE(grp->llen)) < map->m_llen &&
                       orig_llen != cmpxchg_relaxed(&grp->llen,
                                                    orig_llen, map->m_llen))
                        cpu_relax();
                goto got_it;
        }

        work = z_erofs_vle_work_register(&finder, map);
        if (unlikely(work == ERR_PTR(-EAGAIN)))
                goto repeat;

        if (IS_ERR(work))
                return PTR_ERR(work);
got_it:
        z_erofs_pagevec_ctor_init(&builder->vector, Z_EROFS_NR_INLINE_PAGEVECS,
                                  work->pagevec, work->vcnt);

        if (builder->role >= Z_EROFS_VLE_WORK_PRIMARY) {
                /* enable possibly in-place decompression */
                builder->compressed_pages = grp->compressed_pages;
                builder->compressed_deficit = clusterpages;
        } else {
                builder->compressed_pages = NULL;
                builder->compressed_deficit = 0;
        }

        builder->grp = grp;
        builder->work = work;
        return 0;
}

/*
 * keep in mind that no referenced workgroups will be freed
 * only after a RCU grace period, so rcu_read_lock() could
 * prevent a workgroup from being freed.
 */
static void z_erofs_rcu_callback(struct rcu_head *head)
{
        struct z_erofs_vle_work *work = container_of(head,
                struct z_erofs_vle_work, rcu);
        struct z_erofs_vle_workgroup *grp =
                z_erofs_vle_work_workgroup(work, true);

        kmem_cache_free(z_erofs_workgroup_cachep, grp);
}

void erofs_workgroup_free_rcu(struct erofs_workgroup *grp)
{
        struct z_erofs_vle_workgroup *const vgrp = container_of(grp,
                struct z_erofs_vle_workgroup, obj);
        struct z_erofs_vle_work *const work = &vgrp->work;

        call_rcu(&work->rcu, z_erofs_rcu_callback);
}

static void
__z_erofs_vle_work_release(struct z_erofs_vle_workgroup *grp,
                           struct z_erofs_vle_work *work __maybe_unused)
{
        erofs_workgroup_put(&grp->obj);
}

static void z_erofs_vle_work_release(struct z_erofs_vle_work *work)
{
        struct z_erofs_vle_workgroup *grp =
                z_erofs_vle_work_workgroup(work, true);

        __z_erofs_vle_work_release(grp, work);
}

static inline bool
z_erofs_vle_work_iter_end(struct z_erofs_vle_work_builder *builder)
{
        struct z_erofs_vle_work *work = builder->work;

        if (!work)
                return false;

        z_erofs_pagevec_ctor_exit(&builder->vector, false);
        mutex_unlock(&work->lock);

        /*
         * if all pending pages are added, don't hold work reference
         * any longer if the current work isn't hosted by ourselves.
         */
        if (!builder->hosted)
                __z_erofs_vle_work_release(builder->grp, work);

        builder->work = NULL;
        builder->grp = NULL;
        return true;
}

static inline struct page *__stagingpage_alloc(struct list_head *pagepool,
                                               gfp_t gfp)
{
        struct page *page = erofs_allocpage(pagepool, gfp);

        if (unlikely(!page))
                return NULL;

        page->mapping = Z_EROFS_MAPPING_STAGING;
        return page;
}

struct z_erofs_vle_frontend {
        struct inode *const inode;

        struct z_erofs_vle_work_builder builder;
        struct erofs_map_blocks map;

        z_erofs_vle_owned_workgrp_t owned_head;

        /* used for applying cache strategy on the fly */
        bool backmost;
        erofs_off_t headoffset;
};

#define VLE_FRONTEND_INIT(__i) { \
        .inode = __i, \
        .map = { \
                .m_llen = 0, \
                .m_plen = 0, \
                .mpage = NULL \
        }, \
        .builder = VLE_WORK_BUILDER_INIT(), \
        .owned_head = Z_EROFS_VLE_WORKGRP_TAIL, \
        .backmost = true, }

#ifdef EROFS_FS_HAS_MANAGED_CACHE
static inline bool
should_alloc_managed_pages(struct z_erofs_vle_frontend *fe, erofs_off_t la)
{
        if (fe->backmost)
                return true;

        if (EROFS_FS_ZIP_CACHE_LVL >= 2)
                return la < fe->headoffset;

        return false;
}
#else
static inline bool
should_alloc_managed_pages(struct z_erofs_vle_frontend *fe, erofs_off_t la)
{
        return false;
}
#endif

static int z_erofs_do_read_page(struct z_erofs_vle_frontend *fe,
                                struct page *page,
                                struct list_head *page_pool)
{
        struct super_block *const sb = fe->inode->i_sb;
        struct erofs_sb_info *const sbi __maybe_unused = EROFS_SB(sb);
        struct erofs_map_blocks *const map = &fe->map;
        struct z_erofs_vle_work_builder *const builder = &fe->builder;
        const loff_t offset = page_offset(page);

        bool tight = builder_is_hooked(builder);
        struct z_erofs_vle_work *work = builder->work;

        enum z_erofs_cache_alloctype cache_strategy;
        enum z_erofs_page_type page_type;
        unsigned int cur, end, spiltted, index;
        int err = 0;

        /* register locked file pages as online pages in pack */
        z_erofs_onlinepage_init(page);

        spiltted = 0;
        end = PAGE_SIZE;
repeat:
        cur = end - 1;

        /* lucky, within the range of the current map_blocks */
        if (offset + cur >= map->m_la &&
            offset + cur < map->m_la + map->m_llen) {
                /* didn't get a valid unzip work previously (very rare) */
                if (!builder->work)
                        goto restart_now;
                goto hitted;
        }

        /* go ahead the next map_blocks */
        debugln("%s: [out-of-range] pos %llu", __func__, offset + cur);

        if (z_erofs_vle_work_iter_end(builder))
                fe->backmost = false;

        map->m_la = offset + cur;
        map->m_llen = 0;
        err = z_erofs_map_blocks_iter(fe->inode, map, 0);
        if (unlikely(err))
                goto err_out;

restart_now:
        if (unlikely(!(map->m_flags & EROFS_MAP_MAPPED)))
                goto hitted;

        DBG_BUGON(map->m_plen != 1 << sbi->clusterbits);
        DBG_BUGON(erofs_blkoff(map->m_pa));

        err = z_erofs_vle_work_iter_begin(builder, sb, map, &fe->owned_head);
        if (unlikely(err))
                goto err_out;

        /* preload all compressed pages (maybe downgrade role if necessary) */
        if (should_alloc_managed_pages(fe, map->m_la))
                cache_strategy = DELAYEDALLOC;
        else
                cache_strategy = DONTALLOC;

        preload_compressed_pages(builder, MNGD_MAPPING(sbi),
                                 map->m_pa / PAGE_SIZE,
                                 map->m_plen / PAGE_SIZE,
                                 cache_strategy, page_pool, GFP_KERNEL);

        tight &= builder_is_hooked(builder);
        work = builder->work;
hitted:
        cur = end - min_t(unsigned int, offset + end - map->m_la, end);
        if (unlikely(!(map->m_flags & EROFS_MAP_MAPPED))) {
                zero_user_segment(page, cur, end);
                goto next_part;
        }

        /* let's derive page type */
        page_type = cur ? Z_EROFS_VLE_PAGE_TYPE_HEAD :
                (!spiltted ? Z_EROFS_PAGE_TYPE_EXCLUSIVE :
                        (tight ? Z_EROFS_PAGE_TYPE_EXCLUSIVE :
                                Z_EROFS_VLE_PAGE_TYPE_TAIL_SHARED));

        if (cur)
                tight &= builder_is_followed(builder);

retry:
        err = z_erofs_vle_work_add_page(builder, page, page_type);
        /* should allocate an additional staging page for pagevec */
        if (err == -EAGAIN) {
                struct page *const newpage =
                        __stagingpage_alloc(page_pool, GFP_NOFS);

                err = z_erofs_vle_work_add_page(builder, newpage,
                                                Z_EROFS_PAGE_TYPE_EXCLUSIVE);
                if (likely(!err))
                        goto retry;
        }

        if (unlikely(err))
                goto err_out;

        index = page->index - map->m_la / PAGE_SIZE;

        /* FIXME! avoid the last relundant fixup & endio */
        z_erofs_onlinepage_fixup(page, index, true);

        /* bump up the number of spiltted parts of a page */
        ++spiltted;
        /* also update nr_pages */
        work->nr_pages = max_t(pgoff_t, work->nr_pages, index + 1);
next_part:
        /* can be used for verification */
        map->m_llen = offset + cur - map->m_la;

        end = cur;
        if (end > 0)
                goto repeat;

out:
        /* FIXME! avoid the last relundant fixup & endio */
        z_erofs_onlinepage_endio(page);

        debugln("%s, finish page: %pK spiltted: %u map->m_llen %llu",
                __func__, page, spiltted, map->m_llen);
        return err;

        /* if some error occurred while processing this page */
err_out:
        SetPageError(page);
        goto out;
}

static void z_erofs_vle_unzip_kickoff(void *ptr, int bios)
{
        tagptr1_t t = tagptr_init(tagptr1_t, ptr);
        struct z_erofs_vle_unzip_io *io = tagptr_unfold_ptr(t);
        bool background = tagptr_unfold_tags(t);

        if (!background) {
                unsigned long flags;

                spin_lock_irqsave(&io->u.wait.lock, flags);
                if (!atomic_add_return(bios, &io->pending_bios))
                        wake_up_locked(&io->u.wait);
                spin_unlock_irqrestore(&io->u.wait.lock, flags);
                return;
        }

        if (!atomic_add_return(bios, &io->pending_bios))
                queue_work(z_erofs_workqueue, &io->u.work);
}

static inline void z_erofs_vle_read_endio(struct bio *bio)
{
        struct erofs_sb_info *sbi = NULL;
        blk_status_t err = bio->bi_status;
        struct bio_vec *bvec;
        struct bvec_iter_all iter_all;

        bio_for_each_segment_all(bvec, bio, iter_all) {
                struct page *page = bvec->bv_page;
                bool cachemngd = false;

                DBG_BUGON(PageUptodate(page));
                DBG_BUGON(!page->mapping);

                if (unlikely(!sbi && !z_erofs_page_is_staging(page))) {
                        sbi = EROFS_SB(page->mapping->host->i_sb);

                        if (time_to_inject(sbi, FAULT_READ_IO)) {
                                erofs_show_injection_info(FAULT_READ_IO);
                                err = BLK_STS_IOERR;
                        }
                }

                /* sbi should already be gotten if the page is managed */
                if (sbi)
                        cachemngd = erofs_page_is_managed(sbi, page);

                if (unlikely(err))
                        SetPageError(page);
                else if (cachemngd)
                        SetPageUptodate(page);

                if (cachemngd)
                        unlock_page(page);
        }

        z_erofs_vle_unzip_kickoff(bio->bi_private, -1);
        bio_put(bio);
}

static struct page *z_pagemap_global[Z_EROFS_VLE_VMAP_GLOBAL_PAGES];
static DEFINE_MUTEX(z_pagemap_global_lock);

static int z_erofs_vle_unzip(struct super_block *sb,
                             struct z_erofs_vle_workgroup *grp,
                             struct list_head *page_pool)
{
        struct erofs_sb_info *const sbi = EROFS_SB(sb);
        const unsigned int clusterpages = erofs_clusterpages(sbi);

        struct z_erofs_pagevec_ctor ctor;
        unsigned int nr_pages;
        unsigned int sparsemem_pages = 0;
        struct page *pages_onstack[Z_EROFS_VLE_VMAP_ONSTACK_PAGES];
        struct page **pages, **compressed_pages, *page;
        unsigned int algorithm;
        unsigned int i, outputsize;

        enum z_erofs_page_type page_type;
        bool overlapped, partial;
        struct z_erofs_vle_work *work;
        int err;

        might_sleep();
        work = z_erofs_vle_grab_primary_work(grp);
        DBG_BUGON(!READ_ONCE(work->nr_pages));

        mutex_lock(&work->lock);
        nr_pages = work->nr_pages;

        if (likely(nr_pages <= Z_EROFS_VLE_VMAP_ONSTACK_PAGES))
                pages = pages_onstack;
        else if (nr_pages <= Z_EROFS_VLE_VMAP_GLOBAL_PAGES &&
                 mutex_trylock(&z_pagemap_global_lock))
                pages = z_pagemap_global;
        else {
repeat:
                pages = kvmalloc_array(nr_pages, sizeof(struct page *),
                                       GFP_KERNEL);

                /* fallback to global pagemap for the lowmem scenario */
                if (unlikely(!pages)) {
                        if (nr_pages > Z_EROFS_VLE_VMAP_GLOBAL_PAGES)
                                goto repeat;
                        else {
                                mutex_lock(&z_pagemap_global_lock);
                                pages = z_pagemap_global;
                        }
                }
        }

        for (i = 0; i < nr_pages; ++i)
                pages[i] = NULL;

        z_erofs_pagevec_ctor_init(&ctor, Z_EROFS_NR_INLINE_PAGEVECS,
                                  work->pagevec, 0);

        for (i = 0; i < work->vcnt; ++i) {
                unsigned int pagenr;

                page = z_erofs_pagevec_ctor_dequeue(&ctor, &page_type);

                /* all pages in pagevec ought to be valid */
                DBG_BUGON(!page);
                DBG_BUGON(!page->mapping);

                if (z_erofs_put_stagingpage(page_pool, page))
                        continue;

                if (page_type == Z_EROFS_VLE_PAGE_TYPE_HEAD)
                        pagenr = 0;
                else
                        pagenr = z_erofs_onlinepage_index(page);

                DBG_BUGON(pagenr >= nr_pages);
                DBG_BUGON(pages[pagenr]);

                pages[pagenr] = page;
        }
        sparsemem_pages = i;

        z_erofs_pagevec_ctor_exit(&ctor, true);

        overlapped = false;
        compressed_pages = grp->compressed_pages;

        err = 0;
        for (i = 0; i < clusterpages; ++i) {
                unsigned int pagenr;

                page = compressed_pages[i];

                /* all compressed pages ought to be valid */
                DBG_BUGON(!page);
                DBG_BUGON(!page->mapping);

                if (!z_erofs_page_is_staging(page)) {
                        if (erofs_page_is_managed(sbi, page)) {
                                if (unlikely(!PageUptodate(page)))
                                        err = -EIO;
                                continue;
                        }

                        /*
                         * only if non-head page can be selected
                         * for inplace decompression
                         */
                        pagenr = z_erofs_onlinepage_index(page);

                        DBG_BUGON(pagenr >= nr_pages);
                        DBG_BUGON(pages[pagenr]);
                        ++sparsemem_pages;
                        pages[pagenr] = page;

                        overlapped = true;
                }

                /* PG_error needs checking for inplaced and staging pages */
                if (unlikely(PageError(page))) {
                        DBG_BUGON(PageUptodate(page));
                        err = -EIO;
                }
        }

        if (unlikely(err))
                goto out;

        if (nr_pages << PAGE_SHIFT >= work->pageofs + grp->llen) {
                outputsize = grp->llen;
                partial = !(grp->flags & Z_EROFS_VLE_WORKGRP_FULL_LENGTH);
        } else {
                outputsize = (nr_pages << PAGE_SHIFT) - work->pageofs;
                partial = true;
        }

        if (z_erofs_vle_workgrp_fmt(grp) == Z_EROFS_VLE_WORKGRP_FMT_PLAIN)
                algorithm = Z_EROFS_COMPRESSION_SHIFTED;
        else
                algorithm = Z_EROFS_COMPRESSION_LZ4;

        err = z_erofs_decompress(&(struct z_erofs_decompress_req) {
                                        .sb = sb,
                                        .in = compressed_pages,
                                        .out = pages,
                                        .pageofs_out = work->pageofs,
                                        .inputsize = PAGE_SIZE,
                                        .outputsize = outputsize,
                                        .alg = algorithm,
                                        .inplace_io = overlapped,
                                        .partial_decoding = partial
                                 }, page_pool);

out:
        /* must handle all compressed pages before endding pages */
        for (i = 0; i < clusterpages; ++i) {
                page = compressed_pages[i];

                if (erofs_page_is_managed(sbi, page))
                        continue;

                /* recycle all individual staging pages */
                (void)z_erofs_put_stagingpage(page_pool, page);

                WRITE_ONCE(compressed_pages[i], NULL);
        }

        for (i = 0; i < nr_pages; ++i) {
                page = pages[i];
                if (!page)
                        continue;

                DBG_BUGON(!page->mapping);

                /* recycle all individual staging pages */
                if (z_erofs_put_stagingpage(page_pool, page))
                        continue;

                if (unlikely(err < 0))
                        SetPageError(page);

                z_erofs_onlinepage_endio(page);
        }

        if (pages == z_pagemap_global)
                mutex_unlock(&z_pagemap_global_lock);
        else if (unlikely(pages != pages_onstack))
                kvfree(pages);

        work->nr_pages = 0;
        work->vcnt = 0;

        /* all work locks MUST be taken before the following line */

        WRITE_ONCE(grp->next, Z_EROFS_VLE_WORKGRP_NIL);

        /* all work locks SHOULD be released right now */
        mutex_unlock(&work->lock);

        z_erofs_vle_work_release(work);
        return err;
}

static void z_erofs_vle_unzip_all(struct super_block *sb,
                                  struct z_erofs_vle_unzip_io *io,
                                  struct list_head *page_pool)
{
        z_erofs_vle_owned_workgrp_t owned = io->head;

        while (owned != Z_EROFS_VLE_WORKGRP_TAIL_CLOSED) {
                struct z_erofs_vle_workgroup *grp;

                /* no possible that 'owned' equals Z_EROFS_WORK_TPTR_TAIL */
                DBG_BUGON(owned == Z_EROFS_VLE_WORKGRP_TAIL);

                /* no possible that 'owned' equals NULL */
                DBG_BUGON(owned == Z_EROFS_VLE_WORKGRP_NIL);

                grp = container_of(owned, struct z_erofs_vle_workgroup, next);
                owned = READ_ONCE(grp->next);

                z_erofs_vle_unzip(sb, grp, page_pool);
        }
}

static void z_erofs_vle_unzip_wq(struct work_struct *work)
{
        struct z_erofs_vle_unzip_io_sb *iosb = container_of(work,
                struct z_erofs_vle_unzip_io_sb, io.u.work);
        LIST_HEAD(page_pool);

        DBG_BUGON(iosb->io.head == Z_EROFS_VLE_WORKGRP_TAIL_CLOSED);
        z_erofs_vle_unzip_all(iosb->sb, &iosb->io, &page_pool);

        put_pages_list(&page_pool);
        kvfree(iosb);
}

static struct page *
pickup_page_for_submission(struct z_erofs_vle_workgroup *grp,
                           unsigned int nr,
                           struct list_head *pagepool,
                           struct address_space *mc,
                           gfp_t gfp)
{
        /* determined at compile time to avoid too many #ifdefs */
        const bool nocache = __builtin_constant_p(mc) ? !mc : false;
        const pgoff_t index = grp->obj.index;
        bool tocache = false;

        struct address_space *mapping;
        struct page *oldpage, *page;

        compressed_page_t t;
        int justfound;

repeat:
        page = READ_ONCE(grp->compressed_pages[nr]);
        oldpage = page;

        if (!page)
                goto out_allocpage;

        /*
         * the cached page has not been allocated and
         * an placeholder is out there, prepare it now.
         */
        if (!nocache && page == PAGE_UNALLOCATED) {
                tocache = true;
                goto out_allocpage;
        }

        /* process the target tagged pointer */
        t = tagptr_init(compressed_page_t, page);
        justfound = tagptr_unfold_tags(t);
        page = tagptr_unfold_ptr(t);

        mapping = READ_ONCE(page->mapping);

        /*
         * if managed cache is disabled, it's no way to
         * get such a cached-like page.
         */
        if (nocache) {
                /* if managed cache is disabled, it is impossible `justfound' */
                DBG_BUGON(justfound);

                /* and it should be locked, not uptodate, and not truncated */
                DBG_BUGON(!PageLocked(page));
                DBG_BUGON(PageUptodate(page));
                DBG_BUGON(!mapping);
                goto out;
        }

        /*
         * unmanaged (file) pages are all locked solidly,
         * therefore it is impossible for `mapping' to be NULL.
         */
        if (mapping && mapping != mc)
                /* ought to be unmanaged pages */
                goto out;

        lock_page(page);

        /* only true if page reclaim goes wrong, should never happen */
        DBG_BUGON(justfound && PagePrivate(page));

        /* the page is still in manage cache */
        if (page->mapping == mc) {
                WRITE_ONCE(grp->compressed_pages[nr], page);

                ClearPageError(page);
                if (!PagePrivate(page)) {
                        /*
                         * impossible to be !PagePrivate(page) for
                         * the current restriction as well if
                         * the page is already in compressed_pages[].
                         */
                        DBG_BUGON(!justfound);

                        justfound = 0;
                        set_page_private(page, (unsigned long)grp);
                        SetPagePrivate(page);
                }

                /* no need to submit io if it is already up-to-date */
                if (PageUptodate(page)) {
                        unlock_page(page);
                        page = NULL;
                }
                goto out;
        }

        /*
         * the managed page has been truncated, it's unsafe to
         * reuse this one, let's allocate a new cache-managed page.
         */
        DBG_BUGON(page->mapping);
        DBG_BUGON(!justfound);

        tocache = true;
        unlock_page(page);
        put_page(page);
out_allocpage:
        page = __stagingpage_alloc(pagepool, gfp);
        if (oldpage != cmpxchg(&grp->compressed_pages[nr], oldpage, page)) {
                list_add(&page->lru, pagepool);
                cpu_relax();
                goto repeat;
        }
        if (nocache || !tocache)
                goto out;
        if (add_to_page_cache_lru(page, mc, index + nr, gfp)) {
                page->mapping = Z_EROFS_MAPPING_STAGING;
                goto out;
        }

        set_page_private(page, (unsigned long)grp);
        SetPagePrivate(page);
out:    /* the only exit (for tracing and debugging) */
        return page;
}

static struct z_erofs_vle_unzip_io *
jobqueue_init(struct super_block *sb,
              struct z_erofs_vle_unzip_io *io,
              bool foreground)
{
        struct z_erofs_vle_unzip_io_sb *iosb;

        if (foreground) {
                /* waitqueue available for foreground io */
                DBG_BUGON(!io);

                init_waitqueue_head(&io->u.wait);
                atomic_set(&io->pending_bios, 0);
                goto out;
        }

        iosb = kvzalloc(sizeof(*iosb), GFP_KERNEL | __GFP_NOFAIL);
        DBG_BUGON(!iosb);

        /* initialize fields in the allocated descriptor */
        io = &iosb->io;
        iosb->sb = sb;
        INIT_WORK(&io->u.work, z_erofs_vle_unzip_wq);
out:
        io->head = Z_EROFS_VLE_WORKGRP_TAIL_CLOSED;
        return io;
}

/* define workgroup jobqueue types */
enum {
#ifdef EROFS_FS_HAS_MANAGED_CACHE
        JQ_BYPASS,
#endif
        JQ_SUBMIT,
        NR_JOBQUEUES,
};

static void *jobqueueset_init(struct super_block *sb,
                              z_erofs_vle_owned_workgrp_t qtail[],
                              struct z_erofs_vle_unzip_io *q[],
                              struct z_erofs_vle_unzip_io *fgq,
                              bool forcefg)
{
#ifdef EROFS_FS_HAS_MANAGED_CACHE
        /*
         * if managed cache is enabled, bypass jobqueue is needed,
         * no need to read from device for all workgroups in this queue.
         */
        q[JQ_BYPASS] = jobqueue_init(sb, fgq + JQ_BYPASS, true);
        qtail[JQ_BYPASS] = &q[JQ_BYPASS]->head;
#endif

        q[JQ_SUBMIT] = jobqueue_init(sb, fgq + JQ_SUBMIT, forcefg);
        qtail[JQ_SUBMIT] = &q[JQ_SUBMIT]->head;

        return tagptr_cast_ptr(tagptr_fold(tagptr1_t, q[JQ_SUBMIT], !forcefg));
}

#ifdef EROFS_FS_HAS_MANAGED_CACHE
static void move_to_bypass_jobqueue(struct z_erofs_vle_workgroup *grp,
                                    z_erofs_vle_owned_workgrp_t qtail[],
                                    z_erofs_vle_owned_workgrp_t owned_head)
{
        z_erofs_vle_owned_workgrp_t *const submit_qtail = qtail[JQ_SUBMIT];
        z_erofs_vle_owned_workgrp_t *const bypass_qtail = qtail[JQ_BYPASS];

        DBG_BUGON(owned_head == Z_EROFS_VLE_WORKGRP_TAIL_CLOSED);
        if (owned_head == Z_EROFS_VLE_WORKGRP_TAIL)
                owned_head = Z_EROFS_VLE_WORKGRP_TAIL_CLOSED;

        WRITE_ONCE(grp->next, Z_EROFS_VLE_WORKGRP_TAIL_CLOSED);

        WRITE_ONCE(*submit_qtail, owned_head);
        WRITE_ONCE(*bypass_qtail, &grp->next);

        qtail[JQ_BYPASS] = &grp->next;
}

static bool postsubmit_is_all_bypassed(struct z_erofs_vle_unzip_io *q[],
                                       unsigned int nr_bios,
                                       bool force_fg)
{
        /*
         * although background is preferred, no one is pending for submission.
         * don't issue workqueue for decompression but drop it directly instead.
         */
        if (force_fg || nr_bios)
                return false;

        kvfree(container_of(q[JQ_SUBMIT],
                            struct z_erofs_vle_unzip_io_sb,
                            io));
        return true;
}
#else
static void move_to_bypass_jobqueue(struct z_erofs_vle_workgroup *grp,
                                    z_erofs_vle_owned_workgrp_t qtail[],
                                    z_erofs_vle_owned_workgrp_t owned_head)
{
        /* impossible to bypass submission for managed cache disabled */
        DBG_BUGON(1);
}

static bool postsubmit_is_all_bypassed(struct z_erofs_vle_unzip_io *q[],
                                       unsigned int nr_bios,
                                       bool force_fg)
{
        /* bios should be >0 if managed cache is disabled */
        DBG_BUGON(!nr_bios);
        return false;
}
#endif

static bool z_erofs_vle_submit_all(struct super_block *sb,
                                   z_erofs_vle_owned_workgrp_t owned_head,
                                   struct list_head *pagepool,
                                   struct z_erofs_vle_unzip_io *fgq,
                                   bool force_fg)
{
        struct erofs_sb_info *const sbi = EROFS_SB(sb);
        const unsigned int clusterpages = erofs_clusterpages(sbi);
        const gfp_t gfp = GFP_NOFS;

        z_erofs_vle_owned_workgrp_t qtail[NR_JOBQUEUES];
        struct z_erofs_vle_unzip_io *q[NR_JOBQUEUES];
        struct bio *bio;
        void *bi_private;
        /* since bio will be NULL, no need to initialize last_index */
        pgoff_t uninitialized_var(last_index);
        bool force_submit = false;
        unsigned int nr_bios;

        if (unlikely(owned_head == Z_EROFS_VLE_WORKGRP_TAIL))
                return false;

        force_submit = false;
        bio = NULL;
        nr_bios = 0;
        bi_private = jobqueueset_init(sb, qtail, q, fgq, force_fg);

        /* by default, all need io submission */
        q[JQ_SUBMIT]->head = owned_head;

        do {
                struct z_erofs_vle_workgroup *grp;
                pgoff_t first_index;
                struct page *page;
                unsigned int i = 0, bypass = 0;
                int err;

                /* no possible 'owned_head' equals the following */
                DBG_BUGON(owned_head == Z_EROFS_VLE_WORKGRP_TAIL_CLOSED);
                DBG_BUGON(owned_head == Z_EROFS_VLE_WORKGRP_NIL);

                grp = container_of(owned_head,
                                   struct z_erofs_vle_workgroup, next);

                /* close the main owned chain at first */
                owned_head = cmpxchg(&grp->next, Z_EROFS_VLE_WORKGRP_TAIL,
                                     Z_EROFS_VLE_WORKGRP_TAIL_CLOSED);

                first_index = grp->obj.index;
                force_submit |= (first_index != last_index + 1);

repeat:
                page = pickup_page_for_submission(grp, i, pagepool,
                                                  MNGD_MAPPING(sbi), gfp);
                if (!page) {
                        force_submit = true;
                        ++bypass;
                        goto skippage;
                }

                if (bio && force_submit) {
submit_bio_retry:
                        __submit_bio(bio, REQ_OP_READ, 0);
                        bio = NULL;
                }

                if (!bio) {
                        bio = erofs_grab_bio(sb, first_index + i,
                                             BIO_MAX_PAGES, bi_private,
                                             z_erofs_vle_read_endio, true);
                        ++nr_bios;
                }

                err = bio_add_page(bio, page, PAGE_SIZE, 0);
                if (err < PAGE_SIZE)
                        goto submit_bio_retry;

                force_submit = false;
                last_index = first_index + i;
skippage:
                if (++i < clusterpages)
                        goto repeat;

                if (bypass < clusterpages)
                        qtail[JQ_SUBMIT] = &grp->next;
                else
                        move_to_bypass_jobqueue(grp, qtail, owned_head);
        } while (owned_head != Z_EROFS_VLE_WORKGRP_TAIL);

        if (bio)
                __submit_bio(bio, REQ_OP_READ, 0);

        if (postsubmit_is_all_bypassed(q, nr_bios, force_fg))
                return true;

        z_erofs_vle_unzip_kickoff(bi_private, nr_bios);
        return true;
}

static void z_erofs_submit_and_unzip(struct z_erofs_vle_frontend *f,
                                     struct list_head *pagepool,
                                     bool force_fg)
{
        struct super_block *sb = f->inode->i_sb;
        struct z_erofs_vle_unzip_io io[NR_JOBQUEUES];

        if (!z_erofs_vle_submit_all(sb, f->owned_head, pagepool, io, force_fg))
                return;

#ifdef EROFS_FS_HAS_MANAGED_CACHE
        z_erofs_vle_unzip_all(sb, &io[JQ_BYPASS], pagepool);
#endif
        if (!force_fg)
                return;

        /* wait until all bios are completed */
        wait_event(io[JQ_SUBMIT].u.wait,
                   !atomic_read(&io[JQ_SUBMIT].pending_bios));

        /* let's synchronous decompression */
        z_erofs_vle_unzip_all(sb, &io[JQ_SUBMIT], pagepool);
}

static int z_erofs_vle_normalaccess_readpage(struct file *file,
                                             struct page *page)
{
        struct inode *const inode = page->mapping->host;
        struct z_erofs_vle_frontend f = VLE_FRONTEND_INIT(inode);
        int err;
        LIST_HEAD(pagepool);

        trace_erofs_readpage(page, false);

        f.headoffset = (erofs_off_t)page->index << PAGE_SHIFT;

        err = z_erofs_do_read_page(&f, page, &pagepool);
        (void)z_erofs_vle_work_iter_end(&f.builder);

        if (err) {
                errln("%s, failed to read, err [%d]", __func__, err);
                goto out;
        }

        z_erofs_submit_and_unzip(&f, &pagepool, true);
out:
        if (f.map.mpage)
                put_page(f.map.mpage);

        /* clean up the remaining free pages */
        put_pages_list(&pagepool);
        return 0;
}

static int z_erofs_vle_normalaccess_readpages(struct file *filp,
                                              struct address_space *mapping,
                                              struct list_head *pages,
                                              unsigned int nr_pages)
{
        struct inode *const inode = mapping->host;
        struct erofs_sb_info *const sbi = EROFS_I_SB(inode);

        bool sync = __should_decompress_synchronously(sbi, nr_pages);
        struct z_erofs_vle_frontend f = VLE_FRONTEND_INIT(inode);
        gfp_t gfp = mapping_gfp_constraint(mapping, GFP_KERNEL);
        struct page *head = NULL;
        LIST_HEAD(pagepool);

        trace_erofs_readpages(mapping->host, lru_to_page(pages),
                              nr_pages, false);

        f.headoffset = (erofs_off_t)lru_to_page(pages)->index << PAGE_SHIFT;

        for (; nr_pages; --nr_pages) {
                struct page *page = lru_to_page(pages);

                prefetchw(&page->flags);
                list_del(&page->lru);

                /*
                 * A pure asynchronous readahead is indicated if
                 * a PG_readahead marked page is hitted at first.
                 * Let's also do asynchronous decompression for this case.
                 */
                sync &= !(PageReadahead(page) && !head);

                if (add_to_page_cache_lru(page, mapping, page->index, gfp)) {
                        list_add(&page->lru, &pagepool);
                        continue;
                }

                set_page_private(page, (unsigned long)head);
                head = page;
        }

        while (head) {
                struct page *page = head;
                int err;

                /* traversal in reverse order */
                head = (void *)page_private(page);

                err = z_erofs_do_read_page(&f, page, &pagepool);
                if (err) {
                        struct erofs_vnode *vi = EROFS_V(inode);

                        errln("%s, readahead error at page %lu of nid %llu",
                              __func__, page->index, vi->nid);
                }

                put_page(page);
        }

        (void)z_erofs_vle_work_iter_end(&f.builder);

        z_erofs_submit_and_unzip(&f, &pagepool, sync);

        if (f.map.mpage)
                put_page(f.map.mpage);

        /* clean up the remaining free pages */
        put_pages_list(&pagepool);
        return 0;
}

const struct address_space_operations z_erofs_vle_normalaccess_aops = {
        .readpage = z_erofs_vle_normalaccess_readpage,
        .readpages = z_erofs_vle_normalaccess_readpages,
};