/*
 * fs/logfs/gc.c        - garbage collection code
 *
 * As should be obvious for Linux kernel code, license is GPLv2
 *
 * Copyright (c) 2005-2008 Joern Engel <joern@logfs.org>
 */
#include "logfs.h"
#include <linux/sched.h>
#include <linux/slab.h>

/*
 * Wear leveling needs to kick in when the difference between low erase
 * counts and high erase counts gets too big.  A good value for "too big"
 * may be somewhat below 10% of maximum erase count for the device.
 * Why not 397, to pick a nice round number with no specific meaning? :)
 *
 * WL_RATELIMIT is the minimum time between two wear level events.  A huge
 * number of segments may fulfil the requirements for wear leveling at the
 * same time.  If that happens we don't want to cause a latency from hell,
 * but just gently pick one segment every so often and minimize overhead.
 */
#define WL_DELTA 397
#define WL_RATELIMIT 100
#define MAX_OBJ_ALIASES 2600
#define SCAN_RATIO 512  /* number of scanned segments per gc'd segment */
#define LIST_SIZE 64    /* base size of candidate lists */
#define SCAN_ROUNDS 128 /* maximum number of complete medium scans */
#define SCAN_ROUNDS_HIGH 4 /* maximum number of higher-level scans */

static int no_free_segments(struct super_block *sb)
{
        struct logfs_super *super = logfs_super(sb);

        return super->s_free_list.count;
}

/* journal has distance -1, top-most ifile layer distance 0 */
static u8 root_distance(struct super_block *sb, gc_level_t __gc_level)
{
        struct logfs_super *super = logfs_super(sb);
        u8 gc_level = (__force u8)__gc_level;

        switch (gc_level) {
        case 0: /* fall through */
        case 1: /* fall through */
        case 2: /* fall through */
        case 3:
                /* file data or indirect blocks */
                return super->s_ifile_levels + super->s_iblock_levels - gc_level;
        case 6: /* fall through */
        case 7: /* fall through */
        case 8: /* fall through */
        case 9:
                /* inode file data or indirect blocks */
                return super->s_ifile_levels - (gc_level - 6);
        default:
                printk(KERN_ERR"LOGFS: segment of unknown level %x found\n",
                                gc_level);
                WARN_ON(1);
                return super->s_ifile_levels + super->s_iblock_levels;
        }
}

static int segment_is_reserved(struct super_block *sb, u32 segno)
{
        struct logfs_super *super = logfs_super(sb);
        struct logfs_area *area;
        void *reserved;
        int i;

        /* Some segments are reserved.  Just pretend they were all valid */
        reserved = btree_lookup32(&super->s_reserved_segments, segno);
        if (reserved)
                return 1;

        /* Currently open segments */
        for_each_area(i) {
                area = super->s_area[i];
                if (area->a_is_open && area->a_segno == segno)
                        return 1;
        }

        return 0;
}

static void logfs_mark_segment_bad(struct super_block *sb, u32 segno)
{
        BUG();
}

/*
 * Returns the bytes consumed by valid objects in this segment.  Object headers
 * are counted, the segment header is not.
 */
static u32 logfs_valid_bytes(struct super_block *sb, u32 segno, u32 *ec,
                gc_level_t *gc_level)
{
        struct logfs_segment_entry se;
        u32 ec_level;

        logfs_get_segment_entry(sb, segno, &se);
        if (se.ec_level == cpu_to_be32(BADSEG) ||
                        se.valid == cpu_to_be32(RESERVED))
                return RESERVED;

        ec_level = be32_to_cpu(se.ec_level);
        *ec = ec_level >> 4;
        *gc_level = GC_LEVEL(ec_level & 0xf);
        return be32_to_cpu(se.valid);
}

static void logfs_cleanse_block(struct super_block *sb, u64 ofs, u64 ino,
                u64 bix, gc_level_t gc_level)
{
        struct inode *inode;
        int err, cookie;

        inode = logfs_safe_iget(sb, ino, &cookie);
        err = logfs_rewrite_block(inode, bix, ofs, gc_level, 0);
        BUG_ON(err);
        logfs_safe_iput(inode, cookie);
}

static u32 logfs_gc_segment(struct super_block *sb, u32 segno)
{
        struct logfs_super *super = logfs_super(sb);
        struct logfs_segment_header sh;
        struct logfs_object_header oh;
        u64 ofs, ino, bix;
        u32 seg_ofs, logical_segno, cleaned = 0;
        int err, len, valid;
        gc_level_t gc_level;

        LOGFS_BUG_ON(segment_is_reserved(sb, segno), sb);

        btree_insert32(&super->s_reserved_segments, segno, (void *)1, GFP_NOFS);
        err = wbuf_read(sb, dev_ofs(sb, segno, 0), sizeof(sh), &sh);
        BUG_ON(err);
        gc_level = GC_LEVEL(sh.level);
        logical_segno = be32_to_cpu(sh.segno);
        if (sh.crc != logfs_crc32(&sh, sizeof(sh), 4)) {
                logfs_mark_segment_bad(sb, segno);
                cleaned = -1;
                goto out;
        }

        for (seg_ofs = LOGFS_SEGMENT_HEADERSIZE;
                        seg_ofs + sizeof(oh) < super->s_segsize; ) {
                ofs = dev_ofs(sb, logical_segno, seg_ofs);
                err = wbuf_read(sb, dev_ofs(sb, segno, seg_ofs), sizeof(oh),
                                &oh);
                BUG_ON(err);

                if (!memchr_inv(&oh, 0xff, sizeof(oh)))
                        break;

                if (oh.crc != logfs_crc32(&oh, sizeof(oh) - 4, 4)) {
                        logfs_mark_segment_bad(sb, segno);
                        cleaned = super->s_segsize - 1;
                        goto out;
                }

                ino = be64_to_cpu(oh.ino);
                bix = be64_to_cpu(oh.bix);
                len = sizeof(oh) + be16_to_cpu(oh.len);
                valid = logfs_is_valid_block(sb, ofs, ino, bix, gc_level);
                if (valid == 1) {
                        logfs_cleanse_block(sb, ofs, ino, bix, gc_level);
                        cleaned += len;
                } else if (valid == 2) {
                        /* Will be invalid upon journal commit */
                        cleaned += len;
                }
                seg_ofs += len;
        }
out:
        btree_remove32(&super->s_reserved_segments, segno);
        return cleaned;
}

static struct gc_candidate *add_list(struct gc_candidate *cand,
                struct candidate_list *list)
{
        struct rb_node **p = &list->rb_tree.rb_node;
        struct rb_node *parent = NULL;
        struct gc_candidate *cur;
        int comp;

        cand->list = list;
        while (*p) {
                parent = *p;
                cur = rb_entry(parent, struct gc_candidate, rb_node);

                if (list->sort_by_ec)
                        comp = cand->erase_count < cur->erase_count;
                else
                        comp = cand->valid < cur->valid;

                if (comp)
                        p = &parent->rb_left;
                else
                        p = &parent->rb_right;
        }
        rb_link_node(&cand->rb_node, parent, p);
        rb_insert_color(&cand->rb_node, &list->rb_tree);

        if (list->count <= list->maxcount) {
                list->count++;
                return NULL;
        }
        cand = rb_entry(rb_last(&list->rb_tree), struct gc_candidate, rb_node);
        rb_erase(&cand->rb_node, &list->rb_tree);
        cand->list = NULL;
        return cand;
}

static void remove_from_list(struct gc_candidate *cand)
{
        struct candidate_list *list = cand->list;

        rb_erase(&cand->rb_node, &list->rb_tree);
        list->count--;
}

static void free_candidate(struct super_block *sb, struct gc_candidate *cand)
{
        struct logfs_super *super = logfs_super(sb);

        btree_remove32(&super->s_cand_tree, cand->segno);
        kfree(cand);
}

u32 get_best_cand(struct super_block *sb, struct candidate_list *list, u32 *ec)
{
        struct gc_candidate *cand;
        u32 segno;

        BUG_ON(list->count == 0);

        cand = rb_entry(rb_first(&list->rb_tree), struct gc_candidate, rb_node);
        remove_from_list(cand);
        segno = cand->segno;
        if (ec)
                *ec = cand->erase_count;
        free_candidate(sb, cand);
        return segno;
}

/*
 * We have several lists to manage segments with.  The reserve_list is used to
 * deal with bad blocks.  We try to keep the best (lowest ec) segments on this
 * list.
 * The free_list contains free segments for normal usage.  It usually gets the
 * second pick after the reserve_list.  But when the free_list is running short
 * it is more important to keep the free_list full than to keep a reserve.
 *
 * Segments that are not free are put onto a per-level low_list.  If we have
 * to run garbage collection, we pick a candidate from there.  All segments on
 * those lists should have at least some free space so GC will make progress.
 *
 * And last we have the ec_list, which is used to pick segments for wear
 * leveling.
 *
 * If all appropriate lists are full, we simply free the candidate and forget
 * about that segment for a while.  We have better candidates for each purpose.
 */
static void __add_candidate(struct super_block *sb, struct gc_candidate *cand)
{
        struct logfs_super *super = logfs_super(sb);
        u32 full = super->s_segsize - LOGFS_SEGMENT_RESERVE;

        if (cand->valid == 0) {
                /* 100% free segments */
                log_gc_noisy("add reserve segment %x (ec %x) at %llx\n",
                                cand->segno, cand->erase_count,
                                dev_ofs(sb, cand->segno, 0));
                cand = add_list(cand, &super->s_reserve_list);
                if (cand) {
                        log_gc_noisy("add free segment %x (ec %x) at %llx\n",
                                        cand->segno, cand->erase_count,
                                        dev_ofs(sb, cand->segno, 0));
                        cand = add_list(cand, &super->s_free_list);
                }
        } else {
                /* good candidates for Garbage Collection */
                if (cand->valid < full)
                        cand = add_list(cand, &super->s_low_list[cand->dist]);
                /* good candidates for wear leveling,
                 * segments that were recently written get ignored */
                if (cand)
                        cand = add_list(cand, &super->s_ec_list);
        }
        if (cand)
                free_candidate(sb, cand);
}

static int add_candidate(struct super_block *sb, u32 segno, u32 valid, u32 ec,
                u8 dist)
{
        struct logfs_super *super = logfs_super(sb);
        struct gc_candidate *cand;

        cand = kmalloc(sizeof(*cand), GFP_NOFS);
        if (!cand)
                return -ENOMEM;

        cand->segno = segno;
        cand->valid = valid;
        cand->erase_count = ec;
        cand->dist = dist;

        btree_insert32(&super->s_cand_tree, segno, cand, GFP_NOFS);
        __add_candidate(sb, cand);
        return 0;
}

static void remove_segment_from_lists(struct super_block *sb, u32 segno)
{
        struct logfs_super *super = logfs_super(sb);
        struct gc_candidate *cand;

        cand = btree_lookup32(&super->s_cand_tree, segno);
        if (cand) {
                remove_from_list(cand);
                free_candidate(sb, cand);
        }
}

static void scan_segment(struct super_block *sb, u32 segno)
{
        u32 valid, ec = 0;
        gc_level_t gc_level = 0;
        u8 dist;

        if (segment_is_reserved(sb, segno))
                return;

        remove_segment_from_lists(sb, segno);
        valid = logfs_valid_bytes(sb, segno, &ec, &gc_level);
        if (valid == RESERVED)
                return;

        dist = root_distance(sb, gc_level);
        add_candidate(sb, segno, valid, ec, dist);
}

static struct gc_candidate *first_in_list(struct candidate_list *list)
{
        if (list->count == 0)
                return NULL;
        return rb_entry(rb_first(&list->rb_tree), struct gc_candidate, rb_node);
}

/*
 * Find the best segment for garbage collection.  Main criterion is
 * the segment requiring the least effort to clean.  Secondary
 * criterion is to GC on the lowest level available.
 *
 * So we search the least effort segment on the lowest level first,
 * then move up and pick another segment iff is requires significantly
 * less effort.  Hence the LOGFS_MAX_OBJECTSIZE in the comparison.
 */
static struct gc_candidate *get_candidate(struct super_block *sb)
{
        struct logfs_super *super = logfs_super(sb);
        int i, max_dist;
        struct gc_candidate *cand = NULL, *this;

        max_dist = min(no_free_segments(sb), LOGFS_NO_AREAS - 1);

        for (i = max_dist; i >= 0; i--) {
                this = first_in_list(&super->s_low_list[i]);
                if (!this)
                        continue;
                if (!cand)
                        cand = this;
                if (this->valid + LOGFS_MAX_OBJECTSIZE <= cand->valid)
                        cand = this;
        }
        return cand;
}

static int __logfs_gc_once(struct super_block *sb, struct gc_candidate *cand)
{
        struct logfs_super *super = logfs_super(sb);
        gc_level_t gc_level;
        u32 cleaned, valid, segno, ec;
        u8 dist;

        if (!cand) {
                log_gc("GC attempted, but no candidate found\n");
                return 0;
        }

        segno = cand->segno;
        dist = cand->dist;
        valid = logfs_valid_bytes(sb, segno, &ec, &gc_level);
        free_candidate(sb, cand);
        log_gc("GC segment #%02x at %llx, %x required, %x free, %x valid, %llx free\n",
                        segno, (u64)segno << super->s_segshift,
                        dist, no_free_segments(sb), valid,
                        super->s_free_bytes);
        cleaned = logfs_gc_segment(sb, segno);
        log_gc("GC segment #%02x complete - now %x valid\n", segno,
                        valid - cleaned);
        BUG_ON(cleaned != valid);
        return 1;
}

static int logfs_gc_once(struct super_block *sb)
{
        struct gc_candidate *cand;

        cand = get_candidate(sb);
        if (cand)
                remove_from_list(cand);
        return __logfs_gc_once(sb, cand);
}

/* returns 1 if a wrap occurs, 0 otherwise */
static int logfs_scan_some(struct super_block *sb)
{
        struct logfs_super *super = logfs_super(sb);
        u32 segno;
        int i, ret = 0;

        segno = super->s_sweeper;
        for (i = SCAN_RATIO; i > 0; i--) {
                segno++;
                if (segno >= super->s_no_segs) {
                        segno = 0;
                        ret = 1;
                        /* Break out of the loop.  We want to read a single
                         * block from the segment size on next invocation if
                         * SCAN_RATIO is set to match block size
                         */
                        break;
                }

                scan_segment(sb, segno);
        }
        super->s_sweeper = segno;
        return ret;
}

/*
 * In principle, this function should loop forever, looking for GC candidates
 * and moving data.  LogFS is designed in such a way that this loop is
 * guaranteed to terminate.
 *
 * Limiting the loop to some iterations serves purely to catch cases when
 * these guarantees have failed.  An actual endless loop is an obvious bug
 * and should be reported as such.
 */
static void __logfs_gc_pass(struct super_block *sb, int target)
{
        struct logfs_super *super = logfs_super(sb);
        struct logfs_block *block;
        int round, progress, last_progress = 0;

        /*
         * Doing too many changes to the segfile at once would result
         * in a large number of aliases.  Write the journal before
         * things get out of hand.
         */
        if (super->s_shadow_tree.no_shadowed_segments >= MAX_OBJ_ALIASES)
                logfs_write_anchor(sb);

        if (no_free_segments(sb) >= target &&
                        super->s_no_object_aliases < MAX_OBJ_ALIASES)
                return;

        log_gc("__logfs_gc_pass(%x)\n", target);
        for (round = 0; round < SCAN_ROUNDS; ) {
                if (no_free_segments(sb) >= target)
                        goto write_alias;

                /* Sync in-memory state with on-medium state in case they
                 * diverged */
                logfs_write_anchor(sb);
                round += logfs_scan_some(sb);
                if (no_free_segments(sb) >= target)
                        goto write_alias;
                progress = logfs_gc_once(sb);
                if (progress)
                        last_progress = round;
                else if (round - last_progress > 2)
                        break;
                continue;

                /*
                 * The goto logic is nasty, I just don't know a better way to
                 * code it.  GC is supposed to ensure two things:
                 * 1. Enough free segments are available.
                 * 2. The number of aliases is bounded.
                 * When 1. is achieved, we take a look at 2. and write back
                 * some alias-containing blocks, if necessary.  However, after
                 * each such write we need to go back to 1., as writes can
                 * consume free segments.
                 */
write_alias:
                if (super->s_no_object_aliases < MAX_OBJ_ALIASES)
                        return;
                if (list_empty(&super->s_object_alias)) {
                        /* All aliases are still in btree */
                        return;
                }
                log_gc("Write back one alias\n");
                block = list_entry(super->s_object_alias.next,
                                struct logfs_block, alias_list);
                block->ops->write_block(block);
                /*
                 * To round off the nasty goto logic, we reset round here.  It
                 * is a safety-net for GC not making any progress and limited
                 * to something reasonably small.  If incremented it for every
                 * single alias, the loop could terminate rather quickly.
                 */
                round = 0;
        }
        LOGFS_BUG(sb);
}

static int wl_ratelimit(struct super_block *sb, u64 *next_event)
{
        struct logfs_super *super = logfs_super(sb);

        if (*next_event < super->s_gec) {
                *next_event = super->s_gec + WL_RATELIMIT;
                return 0;
        }
        return 1;
}

static void logfs_wl_pass(struct super_block *sb)
{
        struct logfs_super *super = logfs_super(sb);
        struct gc_candidate *wl_cand, *free_cand;

        if (wl_ratelimit(sb, &super->s_wl_gec_ostore))
                return;

        wl_cand = first_in_list(&super->s_ec_list);
        if (!wl_cand)
                return;
        free_cand = first_in_list(&super->s_free_list);
        if (!free_cand)
                return;

        if (wl_cand->erase_count < free_cand->erase_count + WL_DELTA) {
                remove_from_list(wl_cand);
                __logfs_gc_once(sb, wl_cand);
        }
}

/*
 * The journal needs wear leveling as well.  But moving the journal is an
 * expensive operation so we try to avoid it as much as possible.  And if we
 * have to do it, we move the whole journal, not individual segments.
 *
 * Ratelimiting is not strictly necessary here, it mainly serves to avoid the
 * calculations.  First we check whether moving the journal would be a
 * significant improvement.  That means that a) the current journal segments
 * have more wear than the future journal segments and b) the current journal
 * segments have more wear than normal ostore segments.
 * Rationale for b) is that we don't have to move the journal if it is aging
 * less than the ostore, even if the reserve segments age even less (they are
 * excluded from wear leveling, after all).
 * Next we check that the superblocks have less wear than the journal.  Since
 * moving the journal requires writing the superblocks, we have to protect the
 * superblocks even more than the journal.
 *
 * Also we double the acceptable wear difference, compared to ostore wear
 * leveling.  Journal data is read and rewritten rapidly, comparatively.  So
 * soft errors have much less time to accumulate and we allow the journal to
 * be a bit worse than the ostore.
 */
static void logfs_journal_wl_pass(struct super_block *sb)
{
        struct logfs_super *super = logfs_super(sb);
        struct gc_candidate *cand;
        u32 min_journal_ec = -1, max_reserve_ec = 0;
        int i;

        if (wl_ratelimit(sb, &super->s_wl_gec_journal))
                return;

        if (super->s_reserve_list.count < super->s_no_journal_segs) {
                /* Reserve is not full enough to move complete journal */
                return;
        }

        journal_for_each(i)
                if (super->s_journal_seg[i])
                        min_journal_ec = min(min_journal_ec,
                                        super->s_journal_ec[i]);
        cand = rb_entry(rb_first(&super->s_free_list.rb_tree),
                        struct gc_candidate, rb_node);
        max_reserve_ec = cand->erase_count;
        for (i = 0; i < 2; i++) {
                struct logfs_segment_entry se;
                u32 segno = seg_no(sb, super->s_sb_ofs[i]);
                u32 ec;

                logfs_get_segment_entry(sb, segno, &se);
                ec = be32_to_cpu(se.ec_level) >> 4;
                max_reserve_ec = max(max_reserve_ec, ec);
        }

        if (min_journal_ec > max_reserve_ec + 2 * WL_DELTA) {
                do_logfs_journal_wl_pass(sb);
        }
}

void logfs_gc_pass(struct super_block *sb)
{
        struct logfs_super *super = logfs_super(sb);

        //BUG_ON(mutex_trylock(&logfs_super(sb)->s_w_mutex));
        /* Write journal before free space is getting saturated with dirty
         * objects.
         */
        if (super->s_dirty_used_bytes + super->s_dirty_free_bytes
                        + LOGFS_MAX_OBJECTSIZE >= super->s_free_bytes)
                logfs_write_anchor(sb);
        __logfs_gc_pass(sb, super->s_total_levels);
        logfs_wl_pass(sb);
        logfs_journal_wl_pass(sb);
}

static int check_area(struct super_block *sb, int i)
{
        struct logfs_super *super = logfs_super(sb);
        struct logfs_area *area = super->s_area[i];
        gc_level_t gc_level;
        u32 cleaned, valid, ec;
        u32 segno = area->a_segno;
        u64 ofs = dev_ofs(sb, area->a_segno, area->a_written_bytes);

        if (!area->a_is_open)
                return 0;

        if (super->s_devops->can_write_buf(sb, ofs) == 0)
                return 0;

        printk(KERN_INFO"LogFS: Possibly incomplete write at %llx\n", ofs);
        /*
         * The device cannot write back the write buffer.  Most likely the
         * wbuf was already written out and the system crashed at some point
         * before the journal commit happened.  In that case we wouldn't have
         * to do anything.  But if the crash happened before the wbuf was
         * written out correctly, we must GC this segment.  So assume the
         * worst and always do the GC run.
         */
        area->a_is_open = 0;
        valid = logfs_valid_bytes(sb, segno, &ec, &gc_level);
        cleaned = logfs_gc_segment(sb, segno);
        if (cleaned != valid)
                return -EIO;
        return 0;
}

int logfs_check_areas(struct super_block *sb)
{
        int i, err;

        for_each_area(i) {
                err = check_area(sb, i);
                if (err)
                        return err;
        }
        return 0;
}

static void logfs_init_candlist(struct candidate_list *list, int maxcount,
                int sort_by_ec)
{
        list->count = 0;
        list->maxcount = maxcount;
        list->sort_by_ec = sort_by_ec;
        list->rb_tree = RB_ROOT;
}

int logfs_init_gc(struct super_block *sb)
{
        struct logfs_super *super = logfs_super(sb);
        int i;

        btree_init_mempool32(&super->s_cand_tree, super->s_btree_pool);
        logfs_init_candlist(&super->s_free_list, LIST_SIZE + SCAN_RATIO, 1);
        logfs_init_candlist(&super->s_reserve_list,
                        super->s_bad_seg_reserve, 1);
        for_each_area(i)
                logfs_init_candlist(&super->s_low_list[i], LIST_SIZE, 0);
        logfs_init_candlist(&super->s_ec_list, LIST_SIZE, 1);
        return 0;
}

static void logfs_cleanup_list(struct super_block *sb,
                struct candidate_list *list)
{
        struct gc_candidate *cand;

        while (list->count) {
                cand = rb_entry(list->rb_tree.rb_node, struct gc_candidate,
                                rb_node);
                remove_from_list(cand);
                free_candidate(sb, cand);
        }
        BUG_ON(list->rb_tree.rb_node);
}

void logfs_cleanup_gc(struct super_block *sb)
{
        struct logfs_super *super = logfs_super(sb);
        int i;

        if (!super->s_free_list.count)
                return;

        /*
         * FIXME: The btree may still contain a single empty node.  So we
         * call the grim visitor to clean up that mess.  Btree code should
         * do it for us, really.
         */
        btree_grim_visitor32(&super->s_cand_tree, 0, NULL);
        logfs_cleanup_list(sb, &super->s_free_list);
        logfs_cleanup_list(sb, &super->s_reserve_list);
        for_each_area(i)
                logfs_cleanup_list(sb, &super->s_low_list[i]);
        logfs_cleanup_list(sb, &super->s_ec_list);
}