/*
 * GPL HEADER START
 *
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 only,
 * as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License version 2 for more details (a copy is included
 * in the LICENSE file that accompanied this code).
 *
 * You should have received a copy of the GNU General Public License
 * version 2 along with this program; If not, see
 * http://www.sun.com/software/products/lustre/docs/GPLv2.pdf
 *
 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
 * CA 95054 USA or visit www.sun.com if you need additional information or
 * have any questions.
 *
 * GPL HEADER END
 */
/*
 * Copyright (c) 2008, 2010, Oracle and/or its affiliates. All rights reserved.
 * Use is subject to license terms.
 *
 * Copyright (c) 2011, 2012, Intel Corporation.
 */
/*
 * This file is part of Lustre, http://www.lustre.org/
 * Lustre is a trademark of Sun Microsystems, Inc.
 *
 * Implementation of cl_page for OSC layer.
 *
 *   Author: Nikita Danilov <nikita.danilov@sun.com>
 */

#define DEBUG_SUBSYSTEM S_OSC

#include "osc_cl_internal.h"

static void osc_lru_del(struct client_obd *cli, struct osc_page *opg, bool del);
static void osc_lru_add(struct client_obd *cli, struct osc_page *opg);
static int osc_lru_reserve(const struct lu_env *env, struct osc_object *obj,
                           struct osc_page *opg);

/** \addtogroup osc
 *  @{
 */

/*
 * Comment out osc_page_protected because it may sleep inside the
 * the client_obd_list_lock.
 * client_obd_list_lock -> osc_ap_completion -> osc_completion ->
 *   -> osc_page_protected -> osc_page_is_dlocked -> osc_match_base
 *   -> ldlm_lock_match -> sptlrpc_import_check_ctx -> sleep.
 */
#if 0
static int osc_page_is_dlocked(const struct lu_env *env,
                               const struct osc_page *opg,
                               enum cl_lock_mode mode, int pending, int unref)
{
        struct cl_page   *page;
        struct osc_object      *obj;
        struct osc_thread_info *info;
        struct ldlm_res_id     *resname;
        struct lustre_handle   *lockh;
        ldlm_policy_data_t     *policy;
        ldlm_mode_t          dlmmode;
        __u64                   flags;

        might_sleep();

        info = osc_env_info(env);
        resname = &info->oti_resname;
        policy = &info->oti_policy;
        lockh = &info->oti_handle;
        page = opg->ops_cl.cpl_page;
        obj = cl2osc(opg->ops_cl.cpl_obj);

        flags = LDLM_FL_TEST_LOCK | LDLM_FL_BLOCK_GRANTED;
        if (pending)
                flags |= LDLM_FL_CBPENDING;

        dlmmode = osc_cl_lock2ldlm(mode) | LCK_PW;
        osc_lock_build_res(env, obj, resname);
        osc_index2policy(policy, page->cp_obj, page->cp_index, page->cp_index);
        return osc_match_base(osc_export(obj), resname, LDLM_EXTENT, policy,
                              dlmmode, &flags, NULL, lockh, unref);
}

/**
 * Checks an invariant that a page in the cache is covered by a lock, as
 * needed.
 */
static int osc_page_protected(const struct lu_env *env,
                              const struct osc_page *opg,
                              enum cl_lock_mode mode, int unref)
{
        struct cl_object_header *hdr;
        struct cl_lock    *scan;
        struct cl_page    *page;
        struct cl_lock_descr    *descr;
        int result;

        LINVRNT(!opg->ops_temp);

        page = opg->ops_cl.cpl_page;
        if (page->cp_owner != NULL &&
            cl_io_top(page->cp_owner)->ci_lockreq == CILR_NEVER)
                /*
                 * If IO is done without locks (liblustre, or lloop), lock is
                 * not required.
                 */
                result = 1;
        else
                /* otherwise check for a DLM lock */
        result = osc_page_is_dlocked(env, opg, mode, 1, unref);
        if (result == 0) {
                /* maybe this page is a part of a lockless io? */
                hdr = cl_object_header(opg->ops_cl.cpl_obj);
                descr = &osc_env_info(env)->oti_descr;
                descr->cld_mode = mode;
                descr->cld_start = page->cp_index;
                descr->cld_end   = page->cp_index;
                spin_lock(&hdr->coh_lock_guard);
                list_for_each_entry(scan, &hdr->coh_locks, cll_linkage) {
                        /*
                         * Lock-less sub-lock has to be either in HELD state
                         * (when io is actively going on), or in CACHED state,
                         * when top-lock is being unlocked:
                         * cl_io_unlock()->cl_unuse()->...->lov_lock_unuse().
                         */
                        if ((scan->cll_state == CLS_HELD ||
                             scan->cll_state == CLS_CACHED) &&
                            cl_lock_ext_match(&scan->cll_descr, descr)) {
                                struct osc_lock *olck;

                                olck = osc_lock_at(scan);
                                result = osc_lock_is_lockless(olck);
                                break;
                        }
                }
                spin_unlock(&hdr->coh_lock_guard);
        }
        return result;
}
#else
static int osc_page_protected(const struct lu_env *env,
                              const struct osc_page *opg,
                              enum cl_lock_mode mode, int unref)
{
        return 1;
}
#endif

/*****************************************************************************
 *
 * Page operations.
 *
 */
static void osc_page_fini(const struct lu_env *env,
                          struct cl_page_slice *slice)
{
        struct osc_page *opg = cl2osc_page(slice);
        CDEBUG(D_TRACE, "%p\n", opg);
        LASSERT(opg->ops_lock == NULL);
}

static void osc_page_transfer_get(struct osc_page *opg, const char *label)
{
        struct cl_page *page = cl_page_top(opg->ops_cl.cpl_page);

        LASSERT(!opg->ops_transfer_pinned);
        cl_page_get(page);
        lu_ref_add_atomic(&page->cp_reference, label, page);
        opg->ops_transfer_pinned = 1;
}

static void osc_page_transfer_put(const struct lu_env *env,
                                  struct osc_page *opg)
{
        struct cl_page *page = cl_page_top(opg->ops_cl.cpl_page);

        if (opg->ops_transfer_pinned) {
                lu_ref_del(&page->cp_reference, "transfer", page);
                opg->ops_transfer_pinned = 0;
                cl_page_put(env, page);
        }
}

/**
 * This is called once for every page when it is submitted for a transfer
 * either opportunistic (osc_page_cache_add()), or immediate
 * (osc_page_submit()).
 */
static void osc_page_transfer_add(const struct lu_env *env,
                                  struct osc_page *opg, enum cl_req_type crt)
{
        struct osc_object *obj = cl2osc(opg->ops_cl.cpl_obj);

        /* ops_lru and ops_inflight share the same field, so take it from LRU
         * first and then use it as inflight. */
        osc_lru_del(osc_cli(obj), opg, false);

        spin_lock(&obj->oo_seatbelt);
        list_add(&opg->ops_inflight, &obj->oo_inflight[crt]);
        opg->ops_submitter = current;
        spin_unlock(&obj->oo_seatbelt);
}

static int osc_page_cache_add(const struct lu_env *env,
                              const struct cl_page_slice *slice,
                              struct cl_io *io)
{
        struct osc_io   *oio = osc_env_io(env);
        struct osc_page *opg = cl2osc_page(slice);
        int result;

        LINVRNT(osc_page_protected(env, opg, CLM_WRITE, 0));

        osc_page_transfer_get(opg, "transfer\0cache");
        result = osc_queue_async_io(env, io, opg);
        if (result != 0)
                osc_page_transfer_put(env, opg);
        else
                osc_page_transfer_add(env, opg, CRT_WRITE);

        /* for sync write, kernel will wait for this page to be flushed before
         * osc_io_end() is called, so release it earlier.
         * for mkwrite(), it's known there is no further pages. */
        if (cl_io_is_sync_write(io) || cl_io_is_mkwrite(io)) {
                if (oio->oi_active != NULL) {
                        osc_extent_release(env, oio->oi_active);
                        oio->oi_active = NULL;
                }
        }

        return result;
}

void osc_index2policy(ldlm_policy_data_t *policy, const struct cl_object *obj,
                      pgoff_t start, pgoff_t end)
{
        memset(policy, 0, sizeof(*policy));
        policy->l_extent.start = cl_offset(obj, start);
        policy->l_extent.end   = cl_offset(obj, end + 1) - 1;
}

static int osc_page_addref_lock(const struct lu_env *env,
                                struct osc_page *opg,
                                struct cl_lock *lock)
{
        struct osc_lock *olock;
        int           rc;

        LASSERT(opg->ops_lock == NULL);

        olock = osc_lock_at(lock);
        if (atomic_inc_return(&olock->ols_pageref) <= 0) {
                atomic_dec(&olock->ols_pageref);
                rc = -ENODATA;
        } else {
                cl_lock_get(lock);
                opg->ops_lock = lock;
                rc = 0;
        }
        return rc;
}

static void osc_page_putref_lock(const struct lu_env *env,
                                 struct osc_page *opg)
{
        struct cl_lock  *lock = opg->ops_lock;
        struct osc_lock *olock;

        LASSERT(lock != NULL);
        olock = osc_lock_at(lock);

        atomic_dec(&olock->ols_pageref);
        opg->ops_lock = NULL;

        cl_lock_put(env, lock);
}

static int osc_page_is_under_lock(const struct lu_env *env,
                                  const struct cl_page_slice *slice,
                                  struct cl_io *unused)
{
        struct cl_lock *lock;
        int          result = -ENODATA;

        lock = cl_lock_at_page(env, slice->cpl_obj, slice->cpl_page,
                               NULL, 1, 0);
        if (lock != NULL) {
                if (osc_page_addref_lock(env, cl2osc_page(slice), lock) == 0)
                        result = -EBUSY;
                cl_lock_put(env, lock);
        }
        return result;
}

static void osc_page_disown(const struct lu_env *env,
                            const struct cl_page_slice *slice,
                            struct cl_io *io)
{
        struct osc_page *opg = cl2osc_page(slice);

        if (unlikely(opg->ops_lock))
                osc_page_putref_lock(env, opg);
}

static void osc_page_completion_read(const struct lu_env *env,
                                     const struct cl_page_slice *slice,
                                     int ioret)
{
        struct osc_page   *opg = cl2osc_page(slice);
        struct osc_object *obj = cl2osc(opg->ops_cl.cpl_obj);

        if (likely(opg->ops_lock))
                osc_page_putref_lock(env, opg);
        osc_lru_add(osc_cli(obj), opg);
}

static void osc_page_completion_write(const struct lu_env *env,
                                      const struct cl_page_slice *slice,
                                      int ioret)
{
        struct osc_page   *opg = cl2osc_page(slice);
        struct osc_object *obj = cl2osc(slice->cpl_obj);

        osc_lru_add(osc_cli(obj), opg);
}

static int osc_page_fail(const struct lu_env *env,
                         const struct cl_page_slice *slice,
                         struct cl_io *unused)
{
        /*
         * Cached read?
         */
        LBUG();
        return 0;
}


static const char *osc_list(struct list_head *head)
{
        return list_empty(head) ? "-" : "+";
}

static inline unsigned long osc_submit_duration(struct osc_page *opg)
{
        if (opg->ops_submit_time == 0)
                return 0;

        return (cfs_time_current() - opg->ops_submit_time);
}

static int osc_page_print(const struct lu_env *env,
                          const struct cl_page_slice *slice,
                          void *cookie, lu_printer_t printer)
{
        struct osc_page       *opg = cl2osc_page(slice);
        struct osc_async_page *oap = &opg->ops_oap;
        struct osc_object     *obj = cl2osc(slice->cpl_obj);
        struct client_obd     *cli = &osc_export(obj)->exp_obd->u.cli;

        return (*printer)(env, cookie, LUSTRE_OSC_NAME "-page@%p: 1< %#x %d %u %s %s > 2< %llu %u %u %#x %#x | %p %p %p > 3< %s %p %d %lu %d > 4< %d %d %d %lu %s | %s %s %s %s > 5< %s %s %s %s | %d %s | %d %s %s>\n",
                          opg,
                          /* 1 */
                          oap->oap_magic, oap->oap_cmd,
                          oap->oap_interrupted,
                          osc_list(&oap->oap_pending_item),
                          osc_list(&oap->oap_rpc_item),
                          /* 2 */
                          oap->oap_obj_off, oap->oap_page_off, oap->oap_count,
                          oap->oap_async_flags, oap->oap_brw_flags,
                          oap->oap_request, oap->oap_cli, obj,
                          /* 3 */
                          osc_list(&opg->ops_inflight),
                          opg->ops_submitter, opg->ops_transfer_pinned,
                          osc_submit_duration(opg), opg->ops_srvlock,
                          /* 4 */
                          cli->cl_r_in_flight, cli->cl_w_in_flight,
                          cli->cl_max_rpcs_in_flight,
                          cli->cl_avail_grant,
                          osc_list(&cli->cl_cache_waiters),
                          osc_list(&cli->cl_loi_ready_list),
                          osc_list(&cli->cl_loi_hp_ready_list),
                          osc_list(&cli->cl_loi_write_list),
                          osc_list(&cli->cl_loi_read_list),
                          /* 5 */
                          osc_list(&obj->oo_ready_item),
                          osc_list(&obj->oo_hp_ready_item),
                          osc_list(&obj->oo_write_item),
                          osc_list(&obj->oo_read_item),
                          atomic_read(&obj->oo_nr_reads),
                          osc_list(&obj->oo_reading_exts),
                          atomic_read(&obj->oo_nr_writes),
                          osc_list(&obj->oo_hp_exts),
                          osc_list(&obj->oo_urgent_exts));
}

static void osc_page_delete(const struct lu_env *env,
                            const struct cl_page_slice *slice)
{
        struct osc_page   *opg = cl2osc_page(slice);
        struct osc_object *obj = cl2osc(opg->ops_cl.cpl_obj);
        int rc;

        LINVRNT(opg->ops_temp || osc_page_protected(env, opg, CLM_READ, 1));

        CDEBUG(D_TRACE, "%p\n", opg);
        osc_page_transfer_put(env, opg);
        rc = osc_teardown_async_page(env, obj, opg);
        if (rc) {
                CL_PAGE_DEBUG(D_ERROR, env, cl_page_top(slice->cpl_page),
                              "Trying to teardown failed: %d\n", rc);
                LASSERT(0);
        }

        spin_lock(&obj->oo_seatbelt);
        if (opg->ops_submitter != NULL) {
                LASSERT(!list_empty(&opg->ops_inflight));
                list_del_init(&opg->ops_inflight);
                opg->ops_submitter = NULL;
        }
        spin_unlock(&obj->oo_seatbelt);

        osc_lru_del(osc_cli(obj), opg, true);
}

void osc_page_clip(const struct lu_env *env, const struct cl_page_slice *slice,
                   int from, int to)
{
        struct osc_page       *opg = cl2osc_page(slice);
        struct osc_async_page *oap = &opg->ops_oap;

        LINVRNT(osc_page_protected(env, opg, CLM_READ, 0));

        opg->ops_from = from;
        opg->ops_to   = to;
        spin_lock(&oap->oap_lock);
        oap->oap_async_flags |= ASYNC_COUNT_STABLE;
        spin_unlock(&oap->oap_lock);
}

static int osc_page_cancel(const struct lu_env *env,
                           const struct cl_page_slice *slice)
{
        struct osc_page *opg = cl2osc_page(slice);
        int rc = 0;

        LINVRNT(osc_page_protected(env, opg, CLM_READ, 0));

        /* Check if the transferring against this page
         * is completed, or not even queued. */
        if (opg->ops_transfer_pinned)
                /* FIXME: may not be interrupted.. */
                rc = osc_cancel_async_page(env, opg);
        LASSERT(ergo(rc == 0, opg->ops_transfer_pinned == 0));
        return rc;
}

static int osc_page_flush(const struct lu_env *env,
                          const struct cl_page_slice *slice,
                          struct cl_io *io)
{
        struct osc_page *opg = cl2osc_page(slice);
        int rc = 0;

        rc = osc_flush_async_page(env, io, opg);
        return rc;
}

static const struct cl_page_operations osc_page_ops = {
        .cpo_fini         = osc_page_fini,
        .cpo_print       = osc_page_print,
        .cpo_delete     = osc_page_delete,
        .cpo_is_under_lock = osc_page_is_under_lock,
        .cpo_disown     = osc_page_disown,
        .io = {
                [CRT_READ] = {
                        .cpo_cache_add  = osc_page_fail,
                        .cpo_completion = osc_page_completion_read
                },
                [CRT_WRITE] = {
                        .cpo_cache_add  = osc_page_cache_add,
                        .cpo_completion = osc_page_completion_write
                }
        },
        .cpo_clip          = osc_page_clip,
        .cpo_cancel      = osc_page_cancel,
        .cpo_flush        = osc_page_flush
};

int osc_page_init(const struct lu_env *env, struct cl_object *obj,
                struct cl_page *page, struct page *vmpage)
{
        struct osc_object *osc = cl2osc(obj);
        struct osc_page   *opg = cl_object_page_slice(obj, page);
        int result;

        opg->ops_from = 0;
        opg->ops_to   = PAGE_CACHE_SIZE;

        result = osc_prep_async_page(osc, opg, vmpage,
                                        cl_offset(obj, page->cp_index));
        if (result == 0) {
                struct osc_io *oio = osc_env_io(env);
                opg->ops_srvlock = osc_io_srvlock(oio);
                cl_page_slice_add(page, &opg->ops_cl, obj,
                                &osc_page_ops);
        }
        /*
         * Cannot assert osc_page_protected() here as read-ahead
         * creates temporary pages outside of a lock.
         */
        /* ops_inflight and ops_lru are the same field, but it doesn't
         * hurt to initialize it twice :-) */
        INIT_LIST_HEAD(&opg->ops_inflight);
        INIT_LIST_HEAD(&opg->ops_lru);

        /* reserve an LRU space for this page */
        if (page->cp_type == CPT_CACHEABLE && result == 0)
                result = osc_lru_reserve(env, osc, opg);

        return result;
}

/**
 * Helper function called by osc_io_submit() for every page in an immediate
 * transfer (i.e., transferred synchronously).
 */
void osc_page_submit(const struct lu_env *env, struct osc_page *opg,
                     enum cl_req_type crt, int brw_flags)
{
        struct osc_async_page *oap = &opg->ops_oap;
        struct osc_object     *obj = oap->oap_obj;

        LINVRNT(osc_page_protected(env, opg,
                                   crt == CRT_WRITE ? CLM_WRITE : CLM_READ, 1));

        LASSERTF(oap->oap_magic == OAP_MAGIC, "Bad oap magic: oap %p, magic 0x%x\n",
                 oap, oap->oap_magic);
        LASSERT(oap->oap_async_flags & ASYNC_READY);
        LASSERT(oap->oap_async_flags & ASYNC_COUNT_STABLE);

        oap->oap_cmd       = crt == CRT_WRITE ? OBD_BRW_WRITE : OBD_BRW_READ;
        oap->oap_page_off  = opg->ops_from;
        oap->oap_count     = opg->ops_to - opg->ops_from;
        oap->oap_brw_flags = OBD_BRW_SYNC | brw_flags;

        if (!client_is_remote(osc_export(obj)) &&
                        capable(CFS_CAP_SYS_RESOURCE)) {
                oap->oap_brw_flags |= OBD_BRW_NOQUOTA;
                oap->oap_cmd |= OBD_BRW_NOQUOTA;
        }

        opg->ops_submit_time = cfs_time_current();
        osc_page_transfer_get(opg, "transfer\0imm");
        osc_page_transfer_add(env, opg, crt);
}

/* --------------- LRU page management ------------------ */

/* OSC is a natural place to manage LRU pages as applications are specialized
 * to write OSC by OSC. Ideally, if one OSC is used more frequently it should
 * occupy more LRU slots. On the other hand, we should avoid using up all LRU
 * slots (client_obd::cl_lru_left) otherwise process has to be put into sleep
 * for free LRU slots - this will be very bad so the algorithm requires each
 * OSC to free slots voluntarily to maintain a reasonable number of free slots
 * at any time.
 */

static DECLARE_WAIT_QUEUE_HEAD(osc_lru_waitq);
static atomic_t osc_lru_waiters = ATOMIC_INIT(0);
/* LRU pages are freed in batch mode. OSC should at least free this
 * number of pages to avoid running out of LRU budget, and.. */
static const int lru_shrink_min = 2 << (20 - PAGE_CACHE_SHIFT);  /* 2M */
/* free this number at most otherwise it will take too long time to finish. */
static const int lru_shrink_max = 32 << (20 - PAGE_CACHE_SHIFT); /* 32M */

/* Check if we can free LRU slots from this OSC. If there exists LRU waiters,
 * we should free slots aggressively. In this way, slots are freed in a steady
 * step to maintain fairness among OSCs.
 *
 * Return how many LRU pages should be freed. */
static int osc_cache_too_much(struct client_obd *cli)
{
        struct cl_client_cache *cache = cli->cl_cache;
        int pages = atomic_read(&cli->cl_lru_in_list) >> 1;

        if (atomic_read(&osc_lru_waiters) > 0 &&
            atomic_read(cli->cl_lru_left) < lru_shrink_max)
                /* drop lru pages aggressively */
                return min(pages, lru_shrink_max);

        /* if it's going to run out LRU slots, we should free some, but not
         * too much to maintain fairness among OSCs. */
        if (atomic_read(cli->cl_lru_left) < cache->ccc_lru_max >> 4) {
                unsigned long tmp;

                tmp = cache->ccc_lru_max / atomic_read(&cache->ccc_users);
                if (pages > tmp)
                        return min(pages, lru_shrink_max);

                return pages > lru_shrink_min ? lru_shrink_min : 0;
        }

        return 0;
}

/* Return how many pages are not discarded in @pvec. */
static int discard_pagevec(const struct lu_env *env, struct cl_io *io,
                           struct cl_page **pvec, int max_index)
{
        int count;
        int i;

        for (count = 0, i = 0; i < max_index; i++) {
                struct cl_page *page = pvec[i];
                if (cl_page_own_try(env, io, page) == 0) {
                        /* free LRU page only if nobody is using it.
                         * This check is necessary to avoid freeing the pages
                         * having already been removed from LRU and pinned
                         * for IO. */
                        if (!cl_page_in_use(page)) {
                                cl_page_unmap(env, io, page);
                                cl_page_discard(env, io, page);
                                ++count;
                        }
                        cl_page_disown(env, io, page);
                }
                cl_page_put(env, page);
                pvec[i] = NULL;
        }
        return max_index - count;
}

/**
 * Drop @target of pages from LRU at most.
 */
int osc_lru_shrink(struct client_obd *cli, int target)
{
        struct cl_env_nest nest;
        struct lu_env *env;
        struct cl_io *io;
        struct cl_object *clobj = NULL;
        struct cl_page **pvec;
        struct osc_page *opg;
        int maxscan = 0;
        int count = 0;
        int index = 0;
        int rc = 0;

        LASSERT(atomic_read(&cli->cl_lru_in_list) >= 0);
        if (atomic_read(&cli->cl_lru_in_list) == 0 || target <= 0)
                return 0;

        env = cl_env_nested_get(&nest);
        if (IS_ERR(env))
                return PTR_ERR(env);

        pvec = osc_env_info(env)->oti_pvec;
        io = &osc_env_info(env)->oti_io;

        client_obd_list_lock(&cli->cl_lru_list_lock);
        atomic_inc(&cli->cl_lru_shrinkers);
        maxscan = min(target << 1, atomic_read(&cli->cl_lru_in_list));
        while (!list_empty(&cli->cl_lru_list)) {
                struct cl_page *page;

                if (--maxscan < 0)
                        break;

                opg = list_entry(cli->cl_lru_list.next, struct osc_page,
                                     ops_lru);
                page = cl_page_top(opg->ops_cl.cpl_page);
                if (cl_page_in_use_noref(page)) {
                        list_move_tail(&opg->ops_lru, &cli->cl_lru_list);
                        continue;
                }

                LASSERT(page->cp_obj != NULL);
                if (clobj != page->cp_obj) {
                        struct cl_object *tmp = page->cp_obj;

                        cl_object_get(tmp);
                        client_obd_list_unlock(&cli->cl_lru_list_lock);

                        if (clobj != NULL) {
                                count -= discard_pagevec(env, io, pvec, index);
                                index = 0;

                                cl_io_fini(env, io);
                                cl_object_put(env, clobj);
                                clobj = NULL;
                        }

                        clobj = tmp;
                        io->ci_obj = clobj;
                        io->ci_ignore_layout = 1;
                        rc = cl_io_init(env, io, CIT_MISC, clobj);

                        client_obd_list_lock(&cli->cl_lru_list_lock);

                        if (rc != 0)
                                break;

                        ++maxscan;
                        continue;
                }

                /* move this page to the end of list as it will be discarded
                 * soon. The page will be finally removed from LRU list in
                 * osc_page_delete().  */
                list_move_tail(&opg->ops_lru, &cli->cl_lru_list);

                /* it's okay to grab a refcount here w/o holding lock because
                 * it has to grab cl_lru_list_lock to delete the page. */
                cl_page_get(page);
                pvec[index++] = page;
                if (++count >= target)
                        break;

                if (unlikely(index == OTI_PVEC_SIZE)) {
                        client_obd_list_unlock(&cli->cl_lru_list_lock);
                        count -= discard_pagevec(env, io, pvec, index);
                        index = 0;

                        client_obd_list_lock(&cli->cl_lru_list_lock);
                }
        }
        client_obd_list_unlock(&cli->cl_lru_list_lock);

        if (clobj != NULL) {
                count -= discard_pagevec(env, io, pvec, index);

                cl_io_fini(env, io);
                cl_object_put(env, clobj);
        }
        cl_env_nested_put(&nest, env);

        atomic_dec(&cli->cl_lru_shrinkers);
        return count > 0 ? count : rc;
}

static void osc_lru_add(struct client_obd *cli, struct osc_page *opg)
{
        bool wakeup = false;

        if (!opg->ops_in_lru)
                return;

        atomic_dec(&cli->cl_lru_busy);
        client_obd_list_lock(&cli->cl_lru_list_lock);
        if (list_empty(&opg->ops_lru)) {
                list_move_tail(&opg->ops_lru, &cli->cl_lru_list);
                atomic_inc_return(&cli->cl_lru_in_list);
                wakeup = atomic_read(&osc_lru_waiters) > 0;
        }
        client_obd_list_unlock(&cli->cl_lru_list_lock);

        if (wakeup) {
                osc_lru_shrink(cli, osc_cache_too_much(cli));
                wake_up_all(&osc_lru_waitq);
        }
}

/* delete page from LRUlist. The page can be deleted from LRUlist for two
 * reasons: redirtied or deleted from page cache. */
static void osc_lru_del(struct client_obd *cli, struct osc_page *opg, bool del)
{
        if (opg->ops_in_lru) {
                client_obd_list_lock(&cli->cl_lru_list_lock);
                if (!list_empty(&opg->ops_lru)) {
                        LASSERT(atomic_read(&cli->cl_lru_in_list) > 0);
                        list_del_init(&opg->ops_lru);
                        atomic_dec(&cli->cl_lru_in_list);
                        if (!del)
                                atomic_inc(&cli->cl_lru_busy);
                } else if (del) {
                        LASSERT(atomic_read(&cli->cl_lru_busy) > 0);
                        atomic_dec(&cli->cl_lru_busy);
                }
                client_obd_list_unlock(&cli->cl_lru_list_lock);
                if (del) {
                        atomic_inc(cli->cl_lru_left);
                        /* this is a great place to release more LRU pages if
                         * this osc occupies too many LRU pages and kernel is
                         * stealing one of them.
                         * cl_lru_shrinkers is to avoid recursive call in case
                         * we're already in the context of osc_lru_shrink(). */
                        if (atomic_read(&cli->cl_lru_shrinkers) == 0 &&
                            !memory_pressure_get())
                                osc_lru_shrink(cli, osc_cache_too_much(cli));
                        wake_up(&osc_lru_waitq);
                }
        } else {
                LASSERT(list_empty(&opg->ops_lru));
        }
}

static inline int max_to_shrink(struct client_obd *cli)
{
        return min(atomic_read(&cli->cl_lru_in_list) >> 1, lru_shrink_max);
}

static int osc_lru_reclaim(struct client_obd *cli)
{
        struct cl_client_cache *cache = cli->cl_cache;
        int max_scans;
        int rc;

        LASSERT(cache != NULL);
        LASSERT(!list_empty(&cache->ccc_lru));

        rc = osc_lru_shrink(cli, lru_shrink_min);
        if (rc != 0) {
                CDEBUG(D_CACHE, "%s: Free %d pages from own LRU: %p.\n",
                        cli->cl_import->imp_obd->obd_name, rc, cli);
                return rc;
        }

        CDEBUG(D_CACHE, "%s: cli %p no free slots, pages: %d, busy: %d.\n",
                cli->cl_import->imp_obd->obd_name, cli,
                atomic_read(&cli->cl_lru_in_list),
                atomic_read(&cli->cl_lru_busy));

        /* Reclaim LRU slots from other client_obd as it can't free enough
         * from its own. This should rarely happen. */
        spin_lock(&cache->ccc_lru_lock);
        cache->ccc_lru_shrinkers++;
        list_move_tail(&cli->cl_lru_osc, &cache->ccc_lru);

        max_scans = atomic_read(&cache->ccc_users);
        while (--max_scans > 0 && !list_empty(&cache->ccc_lru)) {
                cli = list_entry(cache->ccc_lru.next, struct client_obd,
                                        cl_lru_osc);

                CDEBUG(D_CACHE, "%s: cli %p LRU pages: %d, busy: %d.\n",
                        cli->cl_import->imp_obd->obd_name, cli,
                        atomic_read(&cli->cl_lru_in_list),
                        atomic_read(&cli->cl_lru_busy));

                list_move_tail(&cli->cl_lru_osc, &cache->ccc_lru);
                if (atomic_read(&cli->cl_lru_in_list) > 0) {
                        spin_unlock(&cache->ccc_lru_lock);

                        rc = osc_lru_shrink(cli, max_to_shrink(cli));
                        spin_lock(&cache->ccc_lru_lock);
                        if (rc != 0)
                                break;
                }
        }
        spin_unlock(&cache->ccc_lru_lock);

        CDEBUG(D_CACHE, "%s: cli %p freed %d pages.\n",
                cli->cl_import->imp_obd->obd_name, cli, rc);
        return rc;
}

static int osc_lru_reserve(const struct lu_env *env, struct osc_object *obj,
                           struct osc_page *opg)
{
        struct l_wait_info lwi = LWI_INTR(LWI_ON_SIGNAL_NOOP, NULL);
        struct client_obd *cli = osc_cli(obj);
        int rc = 0;

        if (cli->cl_cache == NULL) /* shall not be in LRU */
                return 0;

        LASSERT(atomic_read(cli->cl_lru_left) >= 0);
        while (!atomic_add_unless(cli->cl_lru_left, -1, 0)) {
                int gen;

                /* run out of LRU spaces, try to drop some by itself */
                rc = osc_lru_reclaim(cli);
                if (rc < 0)
                        break;
                if (rc > 0)
                        continue;

                cond_resched();

                /* slowest case, all of caching pages are busy, notifying
                 * other OSCs that we're lack of LRU slots. */
                atomic_inc(&osc_lru_waiters);

                gen = atomic_read(&cli->cl_lru_in_list);
                rc = l_wait_event(osc_lru_waitq,
                                atomic_read(cli->cl_lru_left) > 0 ||
                                (atomic_read(&cli->cl_lru_in_list) > 0 &&
                                 gen != atomic_read(&cli->cl_lru_in_list)),
                                &lwi);

                atomic_dec(&osc_lru_waiters);
                if (rc < 0)
                        break;
        }

        if (rc >= 0) {
                atomic_inc(&cli->cl_lru_busy);
                opg->ops_in_lru = 1;
                rc = 0;
        }

        return rc;
}

/** @} osc */