f2fs: catch up to v4.14-rc1

[GitHub/exynos8895/android_kernel_samsung_universal8895.git] / fs / f2fs / gc.c

/*
 * fs/f2fs/gc.c
 *
 * Copyright (c) 2012 Samsung Electronics Co., Ltd.
 *             http://www.samsung.com/
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 */
#include <linux/fs.h>
#include <linux/module.h>
#include <linux/backing-dev.h>
#include <linux/init.h>
#include <linux/f2fs_fs.h>
#include <linux/kthread.h>
#include <linux/delay.h>
#include <linux/freezer.h>

#include "f2fs.h"
#include "node.h"
#include "segment.h"
#include "gc.h"
#include <trace/events/f2fs.h>

static int gc_thread_func(void *data)
{
        struct f2fs_sb_info *sbi = data;
        struct f2fs_gc_kthread *gc_th = sbi->gc_thread;
        wait_queue_head_t *wq = &sbi->gc_thread->gc_wait_queue_head;
        unsigned int wait_ms;

        wait_ms = gc_th->min_sleep_time;

        set_freezable();
        do {
                wait_event_interruptible_timeout(*wq,
                                kthread_should_stop() || freezing(current) ||
                                gc_th->gc_wake,
                                msecs_to_jiffies(wait_ms));

                /* give it a try one time */
                if (gc_th->gc_wake)
                        gc_th->gc_wake = 0;

                if (try_to_freeze())
                        continue;
                if (kthread_should_stop())
                        break;

                if (sbi->sb->s_writers.frozen >= SB_FREEZE_WRITE) {
                        increase_sleep_time(gc_th, &wait_ms);
                        continue;
                }

#ifdef CONFIG_F2FS_FAULT_INJECTION
                if (time_to_inject(sbi, FAULT_CHECKPOINT)) {
                        f2fs_show_injection_info(FAULT_CHECKPOINT);
                        f2fs_stop_checkpoint(sbi, false);
                }
#endif

                if (!sb_start_write_trylock(sbi->sb))
                        continue;

                /*
                 * [GC triggering condition]
                 * 0. GC is not conducted currently.
                 * 1. There are enough dirty segments.
                 * 2. IO subsystem is idle by checking the # of writeback pages.
                 * 3. IO subsystem is idle by checking the # of requests in
                 *    bdev's request list.
                 *
                 * Note) We have to avoid triggering GCs frequently.
                 * Because it is possible that some segments can be
                 * invalidated soon after by user update or deletion.
                 * So, I'd like to wait some time to collect dirty segments.
                 */
                if (!mutex_trylock(&sbi->gc_mutex))
                        goto next;

                if (gc_th->gc_urgent) {
                        wait_ms = gc_th->urgent_sleep_time;
                        goto do_gc;
                }

                if (!is_idle(sbi)) {
                        increase_sleep_time(gc_th, &wait_ms);
                        mutex_unlock(&sbi->gc_mutex);
                        goto next;
                }

                if (has_enough_invalid_blocks(sbi))
                        decrease_sleep_time(gc_th, &wait_ms);
                else
                        increase_sleep_time(gc_th, &wait_ms);
do_gc:
                stat_inc_bggc_count(sbi);

                /* if return value is not zero, no victim was selected */
                if (f2fs_gc(sbi, test_opt(sbi, FORCE_FG_GC), true, NULL_SEGNO))
                        wait_ms = gc_th->no_gc_sleep_time;

                trace_f2fs_background_gc(sbi->sb, wait_ms,
                                prefree_segments(sbi), free_segments(sbi));

                /* balancing f2fs's metadata periodically */
                f2fs_balance_fs_bg(sbi);
next:
                sb_end_write(sbi->sb);

        } while (!kthread_should_stop());
        return 0;
}

int start_gc_thread(struct f2fs_sb_info *sbi)
{
        struct f2fs_gc_kthread *gc_th;
        dev_t dev = sbi->sb->s_bdev->bd_dev;
        int err = 0;

        gc_th = f2fs_kmalloc(sbi, sizeof(struct f2fs_gc_kthread), GFP_KERNEL);
        if (!gc_th) {
                err = -ENOMEM;
                goto out;
        }

        gc_th->urgent_sleep_time = DEF_GC_THREAD_URGENT_SLEEP_TIME;
        gc_th->min_sleep_time = DEF_GC_THREAD_MIN_SLEEP_TIME;
        gc_th->max_sleep_time = DEF_GC_THREAD_MAX_SLEEP_TIME;
        gc_th->no_gc_sleep_time = DEF_GC_THREAD_NOGC_SLEEP_TIME;

        gc_th->gc_idle = 0;
        gc_th->gc_urgent = 0;
        gc_th->gc_wake= 0;

        sbi->gc_thread = gc_th;
        init_waitqueue_head(&sbi->gc_thread->gc_wait_queue_head);
        sbi->gc_thread->f2fs_gc_task = kthread_run(gc_thread_func, sbi,
                        "f2fs_gc-%u:%u", MAJOR(dev), MINOR(dev));
        if (IS_ERR(gc_th->f2fs_gc_task)) {
                err = PTR_ERR(gc_th->f2fs_gc_task);
                kfree(gc_th);
                sbi->gc_thread = NULL;
        }
out:
        return err;
}

void stop_gc_thread(struct f2fs_sb_info *sbi)
{
        struct f2fs_gc_kthread *gc_th = sbi->gc_thread;
        if (!gc_th)
                return;
        kthread_stop(gc_th->f2fs_gc_task);
        kfree(gc_th);
        sbi->gc_thread = NULL;
}

static int select_gc_type(struct f2fs_gc_kthread *gc_th, int gc_type)
{
        int gc_mode = (gc_type == BG_GC) ? GC_CB : GC_GREEDY;

        if (gc_th && gc_th->gc_idle) {
                if (gc_th->gc_idle == 1)
                        gc_mode = GC_CB;
                else if (gc_th->gc_idle == 2)
                        gc_mode = GC_GREEDY;
        }
        return gc_mode;
}

static void select_policy(struct f2fs_sb_info *sbi, int gc_type,
                        int type, struct victim_sel_policy *p)
{
        struct dirty_seglist_info *dirty_i = DIRTY_I(sbi);

        if (p->alloc_mode == SSR) {
                p->gc_mode = GC_GREEDY;
                p->dirty_segmap = dirty_i->dirty_segmap[type];
                p->max_search = dirty_i->nr_dirty[type];
                p->ofs_unit = 1;
        } else {
                p->gc_mode = select_gc_type(sbi->gc_thread, gc_type);
                p->dirty_segmap = dirty_i->dirty_segmap[DIRTY];
                p->max_search = dirty_i->nr_dirty[DIRTY];
                p->ofs_unit = sbi->segs_per_sec;
        }

        /* we need to check every dirty segments in the FG_GC case */
        if (gc_type != FG_GC && p->max_search > sbi->max_victim_search)
                p->max_search = sbi->max_victim_search;

        /* let's select beginning hot/small space first */
        if (type == CURSEG_HOT_DATA || IS_NODESEG(type))
                p->offset = 0;
        else
                p->offset = SIT_I(sbi)->last_victim[p->gc_mode];
}

static unsigned int get_max_cost(struct f2fs_sb_info *sbi,
                                struct victim_sel_policy *p)
{
        /* SSR allocates in a segment unit */
        if (p->alloc_mode == SSR)
                return sbi->blocks_per_seg;
        if (p->gc_mode == GC_GREEDY)
                return 2 * sbi->blocks_per_seg * p->ofs_unit;
        else if (p->gc_mode == GC_CB)
                return UINT_MAX;
        else /* No other gc_mode */
                return 0;
}

static unsigned int check_bg_victims(struct f2fs_sb_info *sbi)
{
        struct dirty_seglist_info *dirty_i = DIRTY_I(sbi);
        unsigned int secno;

        /*
         * If the gc_type is FG_GC, we can select victim segments
         * selected by background GC before.
         * Those segments guarantee they have small valid blocks.
         */
        for_each_set_bit(secno, dirty_i->victim_secmap, MAIN_SECS(sbi)) {
                if (sec_usage_check(sbi, secno))
                        continue;

                if (no_fggc_candidate(sbi, secno))
                        continue;

                clear_bit(secno, dirty_i->victim_secmap);
                return GET_SEG_FROM_SEC(sbi, secno);
        }
        return NULL_SEGNO;
}

static unsigned int get_cb_cost(struct f2fs_sb_info *sbi, unsigned int segno)
{
        struct sit_info *sit_i = SIT_I(sbi);
        unsigned int secno = GET_SEC_FROM_SEG(sbi, segno);
        unsigned int start = GET_SEG_FROM_SEC(sbi, secno);
        unsigned long long mtime = 0;
        unsigned int vblocks;
        unsigned char age = 0;
        unsigned char u;
        unsigned int i;

        for (i = 0; i < sbi->segs_per_sec; i++)
                mtime += get_seg_entry(sbi, start + i)->mtime;
        vblocks = get_valid_blocks(sbi, segno, true);

        mtime = div_u64(mtime, sbi->segs_per_sec);
        vblocks = div_u64(vblocks, sbi->segs_per_sec);

        u = (vblocks * 100) >> sbi->log_blocks_per_seg;

        /* Handle if the system time has changed by the user */
        if (mtime < sit_i->min_mtime)
                sit_i->min_mtime = mtime;
        if (mtime > sit_i->max_mtime)
                sit_i->max_mtime = mtime;
        if (sit_i->max_mtime != sit_i->min_mtime)
                age = 100 - div64_u64(100 * (mtime - sit_i->min_mtime),
                                sit_i->max_mtime - sit_i->min_mtime);

        return UINT_MAX - ((100 * (100 - u) * age) / (100 + u));
}

static unsigned int get_greedy_cost(struct f2fs_sb_info *sbi,
                                                unsigned int segno)
{
        unsigned int valid_blocks =
                        get_valid_blocks(sbi, segno, true);

        return IS_DATASEG(get_seg_entry(sbi, segno)->type) ?
                                valid_blocks * 2 : valid_blocks;
}

static inline unsigned int get_gc_cost(struct f2fs_sb_info *sbi,
                        unsigned int segno, struct victim_sel_policy *p)
{
        if (p->alloc_mode == SSR)
                return get_seg_entry(sbi, segno)->ckpt_valid_blocks;

        /* alloc_mode == LFS */
        if (p->gc_mode == GC_GREEDY)
                return get_greedy_cost(sbi, segno);
        else
                return get_cb_cost(sbi, segno);
}

static unsigned int count_bits(const unsigned long *addr,
                                unsigned int offset, unsigned int len)
{
        unsigned int end = offset + len, sum = 0;

        while (offset < end) {
                if (test_bit(offset++, addr))
                        ++sum;
        }
        return sum;
}

/*
 * This function is called from two paths.
 * One is garbage collection and the other is SSR segment selection.
 * When it is called during GC, it just gets a victim segment
 * and it does not remove it from dirty seglist.
 * When it is called from SSR segment selection, it finds a segment
 * which has minimum valid blocks and removes it from dirty seglist.
 */
static int get_victim_by_default(struct f2fs_sb_info *sbi,
                unsigned int *result, int gc_type, int type, char alloc_mode)
{
        struct dirty_seglist_info *dirty_i = DIRTY_I(sbi);
        struct sit_info *sm = SIT_I(sbi);
        struct victim_sel_policy p;
        unsigned int secno, last_victim;
        unsigned int last_segment = MAIN_SEGS(sbi);
        unsigned int nsearched = 0;

        mutex_lock(&dirty_i->seglist_lock);

        p.alloc_mode = alloc_mode;
        select_policy(sbi, gc_type, type, &p);

        p.min_segno = NULL_SEGNO;
        p.min_cost = get_max_cost(sbi, &p);

        if (*result != NULL_SEGNO) {
                if (IS_DATASEG(get_seg_entry(sbi, *result)->type) &&
                        get_valid_blocks(sbi, *result, false) &&
                        !sec_usage_check(sbi, GET_SEC_FROM_SEG(sbi, *result)))
                        p.min_segno = *result;
                goto out;
        }

        if (p.max_search == 0)
                goto out;

        last_victim = sm->last_victim[p.gc_mode];
        if (p.alloc_mode == LFS && gc_type == FG_GC) {
                p.min_segno = check_bg_victims(sbi);
                if (p.min_segno != NULL_SEGNO)
                        goto got_it;
        }

        while (1) {
                unsigned long cost;
                unsigned int segno;

                segno = find_next_bit(p.dirty_segmap, last_segment, p.offset);
                if (segno >= last_segment) {
                        if (sm->last_victim[p.gc_mode]) {
                                last_segment =
                                        sm->last_victim[p.gc_mode];
                                sm->last_victim[p.gc_mode] = 0;
                                p.offset = 0;
                                continue;
                        }
                        break;
                }

                p.offset = segno + p.ofs_unit;
                if (p.ofs_unit > 1) {
                        p.offset -= segno % p.ofs_unit;
                        nsearched += count_bits(p.dirty_segmap,
                                                p.offset - p.ofs_unit,
                                                p.ofs_unit);
                } else {
                        nsearched++;
                }

                secno = GET_SEC_FROM_SEG(sbi, segno);

                if (sec_usage_check(sbi, secno))
                        goto next;
                if (gc_type == BG_GC && test_bit(secno, dirty_i->victim_secmap))
                        goto next;
                if (gc_type == FG_GC && p.alloc_mode == LFS &&
                                        no_fggc_candidate(sbi, secno))
                        goto next;

                cost = get_gc_cost(sbi, segno, &p);

                if (p.min_cost > cost) {
                        p.min_segno = segno;
                        p.min_cost = cost;
                }
next:
                if (nsearched >= p.max_search) {
                        if (!sm->last_victim[p.gc_mode] && segno <= last_victim)
                                sm->last_victim[p.gc_mode] = last_victim + 1;
                        else
                                sm->last_victim[p.gc_mode] = segno + 1;
                        sm->last_victim[p.gc_mode] %= MAIN_SEGS(sbi);
                        break;
                }
        }
        if (p.min_segno != NULL_SEGNO) {
got_it:
                if (p.alloc_mode == LFS) {
                        secno = GET_SEC_FROM_SEG(sbi, p.min_segno);
                        if (gc_type == FG_GC)
                                sbi->cur_victim_sec = secno;
                        else
                                set_bit(secno, dirty_i->victim_secmap);
                }
                *result = (p.min_segno / p.ofs_unit) * p.ofs_unit;

                trace_f2fs_get_victim(sbi->sb, type, gc_type, &p,
                                sbi->cur_victim_sec,
                                prefree_segments(sbi), free_segments(sbi));
        }
out:
        mutex_unlock(&dirty_i->seglist_lock);

        return (p.min_segno == NULL_SEGNO) ? 0 : 1;
}

static const struct victim_selection default_v_ops = {
        .get_victim = get_victim_by_default,
};

static struct inode *find_gc_inode(struct gc_inode_list *gc_list, nid_t ino)
{
        struct inode_entry *ie;

        ie = radix_tree_lookup(&gc_list->iroot, ino);
        if (ie)
                return ie->inode;
        return NULL;
}

static void add_gc_inode(struct gc_inode_list *gc_list, struct inode *inode)
{
        struct inode_entry *new_ie;

        if (inode == find_gc_inode(gc_list, inode->i_ino)) {
                iput(inode);
                return;
        }
        new_ie = f2fs_kmem_cache_alloc(inode_entry_slab, GFP_NOFS);
        new_ie->inode = inode;

        f2fs_radix_tree_insert(&gc_list->iroot, inode->i_ino, new_ie);
        list_add_tail(&new_ie->list, &gc_list->ilist);
}

static void put_gc_inode(struct gc_inode_list *gc_list)
{
        struct inode_entry *ie, *next_ie;
        list_for_each_entry_safe(ie, next_ie, &gc_list->ilist, list) {
                radix_tree_delete(&gc_list->iroot, ie->inode->i_ino);
                iput(ie->inode);
                list_del(&ie->list);
                kmem_cache_free(inode_entry_slab, ie);
        }
}

static int check_valid_map(struct f2fs_sb_info *sbi,
                                unsigned int segno, int offset)
{
        struct sit_info *sit_i = SIT_I(sbi);
        struct seg_entry *sentry;
        int ret;

        mutex_lock(&sit_i->sentry_lock);
        sentry = get_seg_entry(sbi, segno);
        ret = f2fs_test_bit(offset, sentry->cur_valid_map);
        mutex_unlock(&sit_i->sentry_lock);
        return ret;
}

/*
 * This function compares node address got in summary with that in NAT.
 * On validity, copy that node with cold status, otherwise (invalid node)
 * ignore that.
 */
static void gc_node_segment(struct f2fs_sb_info *sbi,
                struct f2fs_summary *sum, unsigned int segno, int gc_type)
{
        struct f2fs_summary *entry;
        block_t start_addr;
        int off;
        int phase = 0;

        start_addr = START_BLOCK(sbi, segno);

next_step:
        entry = sum;

        for (off = 0; off < sbi->blocks_per_seg; off++, entry++) {
                nid_t nid = le32_to_cpu(entry->nid);
                struct page *node_page;
                struct node_info ni;

                /* stop BG_GC if there is not enough free sections. */
                if (gc_type == BG_GC && has_not_enough_free_secs(sbi, 0, 0))
                        return;

                if (check_valid_map(sbi, segno, off) == 0)
                        continue;

                if (phase == 0) {
                        ra_meta_pages(sbi, NAT_BLOCK_OFFSET(nid), 1,
                                                        META_NAT, true);
                        continue;
                }

                if (phase == 1) {
                        ra_node_page(sbi, nid);
                        continue;
                }

                /* phase == 2 */
                node_page = get_node_page(sbi, nid);
                if (IS_ERR(node_page))
                        continue;

                /* block may become invalid during get_node_page */
                if (check_valid_map(sbi, segno, off) == 0) {
                        f2fs_put_page(node_page, 1);
                        continue;
                }

                get_node_info(sbi, nid, &ni);
                if (ni.blk_addr != start_addr + off) {
                        f2fs_put_page(node_page, 1);
                        continue;
                }

                move_node_page(node_page, gc_type);
                stat_inc_node_blk_count(sbi, 1, gc_type);
        }

        if (++phase < 3)
                goto next_step;
}

/*
 * Calculate start block index indicating the given node offset.
 * Be careful, caller should give this node offset only indicating direct node
 * blocks. If any node offsets, which point the other types of node blocks such
 * as indirect or double indirect node blocks, are given, it must be a caller's
 * bug.
 */
block_t start_bidx_of_node(unsigned int node_ofs, struct inode *inode)
{
        unsigned int indirect_blks = 2 * NIDS_PER_BLOCK + 4;
        unsigned int bidx;

        if (node_ofs == 0)
                return 0;

        if (node_ofs <= 2) {
                bidx = node_ofs - 1;
        } else if (node_ofs <= indirect_blks) {
                int dec = (node_ofs - 4) / (NIDS_PER_BLOCK + 1);
                bidx = node_ofs - 2 - dec;
        } else {
                int dec = (node_ofs - indirect_blks - 3) / (NIDS_PER_BLOCK + 1);
                bidx = node_ofs - 5 - dec;
        }
        return bidx * ADDRS_PER_BLOCK + ADDRS_PER_INODE(inode);
}

static bool is_alive(struct f2fs_sb_info *sbi, struct f2fs_summary *sum,
                struct node_info *dni, block_t blkaddr, unsigned int *nofs)
{
        struct page *node_page;
        nid_t nid;
        unsigned int ofs_in_node;
        block_t source_blkaddr;

        nid = le32_to_cpu(sum->nid);
        ofs_in_node = le16_to_cpu(sum->ofs_in_node);

        node_page = get_node_page(sbi, nid);
        if (IS_ERR(node_page))
                return false;

        get_node_info(sbi, nid, dni);

        if (sum->version != dni->version) {
                f2fs_msg(sbi->sb, KERN_WARNING,
                                "%s: valid data with mismatched node version.",
                                __func__);
                set_sbi_flag(sbi, SBI_NEED_FSCK);
        }

        *nofs = ofs_of_node(node_page);
        source_blkaddr = datablock_addr(NULL, node_page, ofs_in_node);
        f2fs_put_page(node_page, 1);

        if (source_blkaddr != blkaddr)
                return false;
        return true;
}

/*
 * Move data block via META_MAPPING while keeping locked data page.
 * This can be used to move blocks, aka LBAs, directly on disk.
 */
static void move_data_block(struct inode *inode, block_t bidx,
                                        unsigned int segno, int off)
{
        struct f2fs_io_info fio = {
                .sbi = F2FS_I_SB(inode),
                .type = DATA,
                .temp = COLD,
                .op = REQ_OP_READ,
                .op_flags = REQ_SYNC,
                .encrypted_page = NULL,
                .in_list = false,
        };
        struct dnode_of_data dn;
        struct f2fs_summary sum;
        struct node_info ni;
        struct page *page;
        block_t newaddr;
        int err;

        /* do not read out */
        page = f2fs_grab_cache_page(inode->i_mapping, bidx, false);
        if (!page)
                return;

        if (!check_valid_map(F2FS_I_SB(inode), segno, off))
                goto out;

        if (f2fs_is_atomic_file(inode))
                goto out;

        set_new_dnode(&dn, inode, NULL, NULL, 0);
        err = get_dnode_of_data(&dn, bidx, LOOKUP_NODE);
        if (err)
                goto out;

        if (unlikely(dn.data_blkaddr == NULL_ADDR)) {
                ClearPageUptodate(page);
                goto put_out;
        }

        /*
         * don't cache encrypted data into meta inode until previous dirty
         * data were writebacked to avoid racing between GC and flush.
         */
        f2fs_wait_on_page_writeback(page, DATA, true);

        get_node_info(fio.sbi, dn.nid, &ni);
        set_summary(&sum, dn.nid, dn.ofs_in_node, ni.version);

        /* read page */
        fio.page = page;
        fio.new_blkaddr = fio.old_blkaddr = dn.data_blkaddr;

        allocate_data_block(fio.sbi, NULL, fio.old_blkaddr, &newaddr,
                                        &sum, CURSEG_COLD_DATA, NULL, false);

        fio.encrypted_page = pagecache_get_page(META_MAPPING(fio.sbi), newaddr,
                                        FGP_LOCK | FGP_CREAT, GFP_NOFS);
        if (!fio.encrypted_page) {
                err = -ENOMEM;
                goto recover_block;
        }

        err = f2fs_submit_page_bio(&fio);
        if (err)
                goto put_page_out;

        /* write page */
        lock_page(fio.encrypted_page);

        if (unlikely(fio.encrypted_page->mapping != META_MAPPING(fio.sbi))) {
                err = -EIO;
                goto put_page_out;
        }
        if (unlikely(!PageUptodate(fio.encrypted_page))) {
                err = -EIO;
                goto put_page_out;
        }

        set_page_dirty(fio.encrypted_page);
        f2fs_wait_on_page_writeback(fio.encrypted_page, DATA, true);
        if (clear_page_dirty_for_io(fio.encrypted_page))
                dec_page_count(fio.sbi, F2FS_DIRTY_META);

        set_page_writeback(fio.encrypted_page);

        /* allocate block address */
        f2fs_wait_on_page_writeback(dn.node_page, NODE, true);

        fio.op = REQ_OP_WRITE;
        fio.op_flags = REQ_SYNC | REQ_NOIDLE;
        fio.new_blkaddr = newaddr;
        f2fs_submit_page_write(&fio);

        f2fs_update_iostat(fio.sbi, FS_GC_DATA_IO, F2FS_BLKSIZE);

        f2fs_update_data_blkaddr(&dn, newaddr);
        set_inode_flag(inode, FI_APPEND_WRITE);
        if (page->index == 0)
                set_inode_flag(inode, FI_FIRST_BLOCK_WRITTEN);
put_page_out:
        f2fs_put_page(fio.encrypted_page, 1);
recover_block:
        if (err)
                __f2fs_replace_block(fio.sbi, &sum, newaddr, fio.old_blkaddr,
                                                                true, true);
put_out:
        f2fs_put_dnode(&dn);
out:
        f2fs_put_page(page, 1);
}

static void move_data_page(struct inode *inode, block_t bidx, int gc_type,
                                                        unsigned int segno, int off)
{
        struct page *page;

        page = get_lock_data_page(inode, bidx, true);
        if (IS_ERR(page))
                return;

        if (!check_valid_map(F2FS_I_SB(inode), segno, off))
                goto out;

        if (f2fs_is_atomic_file(inode))
                goto out;

        if (gc_type == BG_GC) {
                if (PageWriteback(page))
                        goto out;
                set_page_dirty(page);
                set_cold_data(page);
        } else {
                struct f2fs_io_info fio = {
                        .sbi = F2FS_I_SB(inode),
                        .type = DATA,
                        .temp = COLD,
                        .op = REQ_OP_WRITE,
                        .op_flags = REQ_SYNC,
                        .old_blkaddr = NULL_ADDR,
                        .page = page,
                        .encrypted_page = NULL,
                        .need_lock = LOCK_REQ,
                        .io_type = FS_GC_DATA_IO,
                };
                bool is_dirty = PageDirty(page);
                int err;

retry:
                set_page_dirty(page);
                f2fs_wait_on_page_writeback(page, DATA, true);
                if (clear_page_dirty_for_io(page)) {
                        inode_dec_dirty_pages(inode);
                        remove_dirty_inode(inode);
                }

                set_cold_data(page);

                err = do_write_data_page(&fio);
                if (err == -ENOMEM && is_dirty) {
                        congestion_wait(BLK_RW_ASYNC, HZ/50);
                        goto retry;
                }
        }
out:
        f2fs_put_page(page, 1);
}

/*
 * This function tries to get parent node of victim data block, and identifies
 * data block validity. If the block is valid, copy that with cold status and
 * modify parent node.
 * If the parent node is not valid or the data block address is different,
 * the victim data block is ignored.
 */
static void gc_data_segment(struct f2fs_sb_info *sbi, struct f2fs_summary *sum,
                struct gc_inode_list *gc_list, unsigned int segno, int gc_type)
{
        struct super_block *sb = sbi->sb;
        struct f2fs_summary *entry;
        block_t start_addr;
        int off;
        int phase = 0;

        start_addr = START_BLOCK(sbi, segno);

next_step:
        entry = sum;

        for (off = 0; off < sbi->blocks_per_seg; off++, entry++) {
                struct page *data_page;
                struct inode *inode;
                struct node_info dni; /* dnode info for the data */
                unsigned int ofs_in_node, nofs;
                block_t start_bidx;
                nid_t nid = le32_to_cpu(entry->nid);

                /* stop BG_GC if there is not enough free sections. */
                if (gc_type == BG_GC && has_not_enough_free_secs(sbi, 0, 0))
                        return;

                if (check_valid_map(sbi, segno, off) == 0)
                        continue;

                if (phase == 0) {
                        ra_meta_pages(sbi, NAT_BLOCK_OFFSET(nid), 1,
                                                        META_NAT, true);
                        continue;
                }

                if (phase == 1) {
                        ra_node_page(sbi, nid);
                        continue;
                }

                /* Get an inode by ino with checking validity */
                if (!is_alive(sbi, entry, &dni, start_addr + off, &nofs))
                        continue;

                if (phase == 2) {
                        ra_node_page(sbi, dni.ino);
                        continue;
                }

                ofs_in_node = le16_to_cpu(entry->ofs_in_node);

                if (phase == 3) {
                        inode = f2fs_iget(sb, dni.ino);
                        if (IS_ERR(inode) || is_bad_inode(inode))
                                continue;

                        /* if encrypted inode, let's go phase 3 */
                        if (f2fs_encrypted_file(inode)) {
                                add_gc_inode(gc_list, inode);
                                continue;
                        }

                        start_bidx = start_bidx_of_node(nofs, inode);
                        data_page = get_read_data_page(inode,
                                        start_bidx + ofs_in_node, REQ_RAHEAD,
                                        true);
                        if (IS_ERR(data_page)) {
                                iput(inode);
                                continue;
                        }

                        f2fs_put_page(data_page, 0);
                        add_gc_inode(gc_list, inode);
                        continue;
                }

                /* phase 4 */
                inode = find_gc_inode(gc_list, dni.ino);
                if (inode) {
                        struct f2fs_inode_info *fi = F2FS_I(inode);
                        bool locked = false;

                        if (S_ISREG(inode->i_mode)) {
                                if (!down_write_trylock(&fi->dio_rwsem[READ]))
                                        continue;
                                if (!down_write_trylock(
                                                &fi->dio_rwsem[WRITE])) {
                                        up_write(&fi->dio_rwsem[READ]);
                                        continue;
                                }
                                locked = true;

                                /* wait for all inflight aio data */
                                inode_dio_wait(inode);
                        }

                        start_bidx = start_bidx_of_node(nofs, inode)
                                                                + ofs_in_node;
                        if (f2fs_encrypted_file(inode))
                                move_data_block(inode, start_bidx, segno, off);
                        else
                                move_data_page(inode, start_bidx, gc_type,
                                                                segno, off);

                        if (locked) {
                                up_write(&fi->dio_rwsem[WRITE]);
                                up_write(&fi->dio_rwsem[READ]);
                        }

                        stat_inc_data_blk_count(sbi, 1, gc_type);
                }
        }

        if (++phase < 5)
                goto next_step;
}

static int __get_victim(struct f2fs_sb_info *sbi, unsigned int *victim,
                        int gc_type)
{
        struct sit_info *sit_i = SIT_I(sbi);
        int ret;

        mutex_lock(&sit_i->sentry_lock);
        ret = DIRTY_I(sbi)->v_ops->get_victim(sbi, victim, gc_type,
                                              NO_CHECK_TYPE, LFS);
        mutex_unlock(&sit_i->sentry_lock);
        return ret;
}

static int do_garbage_collect(struct f2fs_sb_info *sbi,
                                unsigned int start_segno,
                                struct gc_inode_list *gc_list, int gc_type)
{
        struct page *sum_page;
        struct f2fs_summary_block *sum;
        struct blk_plug plug;
        unsigned int segno = start_segno;
        unsigned int end_segno = start_segno + sbi->segs_per_sec;
        int seg_freed = 0;
        unsigned char type = IS_DATASEG(get_seg_entry(sbi, segno)->type) ?
                                                SUM_TYPE_DATA : SUM_TYPE_NODE;

        /* readahead multi ssa blocks those have contiguous address */
        if (sbi->segs_per_sec > 1)
                ra_meta_pages(sbi, GET_SUM_BLOCK(sbi, segno),
                                        sbi->segs_per_sec, META_SSA, true);

        /* reference all summary page */
        while (segno < end_segno) {
                sum_page = get_sum_page(sbi, segno++);
                unlock_page(sum_page);
        }

        blk_start_plug(&plug);

        for (segno = start_segno; segno < end_segno; segno++) {

                /* find segment summary of victim */
                sum_page = find_get_page(META_MAPPING(sbi),
                                        GET_SUM_BLOCK(sbi, segno));
                f2fs_put_page(sum_page, 0);

                if (get_valid_blocks(sbi, segno, false) == 0 ||
                                !PageUptodate(sum_page) ||
                                unlikely(f2fs_cp_error(sbi)))
                        goto next;

                sum = page_address(sum_page);
                f2fs_bug_on(sbi, type != GET_SUM_TYPE((&sum->footer)));

                /*
                 * this is to avoid deadlock:
                 * - lock_page(sum_page)         - f2fs_replace_block
                 *  - check_valid_map()            - mutex_lock(sentry_lock)
                 *   - mutex_lock(sentry_lock)     - change_curseg()
                 *                                  - lock_page(sum_page)
                 */
                if (type == SUM_TYPE_NODE)
                        gc_node_segment(sbi, sum->entries, segno, gc_type);
                else
                        gc_data_segment(sbi, sum->entries, gc_list, segno,
                                                                gc_type);

                stat_inc_seg_count(sbi, type, gc_type);

                if (gc_type == FG_GC &&
                                get_valid_blocks(sbi, segno, false) == 0)
                        seg_freed++;
next:
                f2fs_put_page(sum_page, 0);
        }

        if (gc_type == FG_GC)
                f2fs_submit_merged_write(sbi,
                                (type == SUM_TYPE_NODE) ? NODE : DATA);

        blk_finish_plug(&plug);

        stat_inc_call_count(sbi->stat_info);

        return seg_freed;
}

int f2fs_gc(struct f2fs_sb_info *sbi, bool sync,
                        bool background, unsigned int segno)
{
        int gc_type = sync ? FG_GC : BG_GC;
        int sec_freed = 0, seg_freed = 0, total_freed = 0;
        int ret = 0;
        struct cp_control cpc;
        unsigned int init_segno = segno;
        struct gc_inode_list gc_list = {
                .ilist = LIST_HEAD_INIT(gc_list.ilist),
                .iroot = RADIX_TREE_INIT(GFP_NOFS),
        };

        trace_f2fs_gc_begin(sbi->sb, sync, background,
                                get_pages(sbi, F2FS_DIRTY_NODES),
                                get_pages(sbi, F2FS_DIRTY_DENTS),
                                get_pages(sbi, F2FS_DIRTY_IMETA),
                                free_sections(sbi),
                                free_segments(sbi),
                                reserved_segments(sbi),
                                prefree_segments(sbi));

        cpc.reason = __get_cp_reason(sbi);
gc_more:
        if (unlikely(!(sbi->sb->s_flags & MS_ACTIVE))) {
                ret = -EINVAL;
                goto stop;
        }
        if (unlikely(f2fs_cp_error(sbi))) {
                ret = -EIO;
                goto stop;
        }

        if (gc_type == BG_GC && has_not_enough_free_secs(sbi, 0, 0)) {
                /*
                 * For example, if there are many prefree_segments below given
                 * threshold, we can make them free by checkpoint. Then, we
                 * secure free segments which doesn't need fggc any more.
                 */
                if (prefree_segments(sbi)) {
                        ret = write_checkpoint(sbi, &cpc);
                        if (ret)
                                goto stop;
                }
                if (has_not_enough_free_secs(sbi, 0, 0))
                        gc_type = FG_GC;
        }

        /* f2fs_balance_fs doesn't need to do BG_GC in critical path. */
        if (gc_type == BG_GC && !background) {
                ret = -EINVAL;
                goto stop;
        }
        if (!__get_victim(sbi, &segno, gc_type)) {
                ret = -ENODATA;
                goto stop;
        }

        seg_freed = do_garbage_collect(sbi, segno, &gc_list, gc_type);
        if (gc_type == FG_GC && seg_freed == sbi->segs_per_sec)
                sec_freed++;
        total_freed += seg_freed;

        if (gc_type == FG_GC)
                sbi->cur_victim_sec = NULL_SEGNO;

        if (!sync) {
                if (has_not_enough_free_secs(sbi, sec_freed, 0)) {
                        segno = NULL_SEGNO;
                        goto gc_more;
                }

                if (gc_type == FG_GC)
                        ret = write_checkpoint(sbi, &cpc);
        }
stop:
        SIT_I(sbi)->last_victim[ALLOC_NEXT] = 0;
        SIT_I(sbi)->last_victim[FLUSH_DEVICE] = init_segno;

        trace_f2fs_gc_end(sbi->sb, ret, total_freed, sec_freed,
                                get_pages(sbi, F2FS_DIRTY_NODES),
                                get_pages(sbi, F2FS_DIRTY_DENTS),
                                get_pages(sbi, F2FS_DIRTY_IMETA),
                                free_sections(sbi),
                                free_segments(sbi),
                                reserved_segments(sbi),
                                prefree_segments(sbi));

        mutex_unlock(&sbi->gc_mutex);

        put_gc_inode(&gc_list);

        if (sync)
                ret = sec_freed ? 0 : -EAGAIN;
        return ret;
}

void build_gc_manager(struct f2fs_sb_info *sbi)
{
        u64 main_count, resv_count, ovp_count;

        DIRTY_I(sbi)->v_ops = &default_v_ops;

        /* threshold of # of valid blocks in a section for victims of FG_GC */
        main_count = SM_I(sbi)->main_segments << sbi->log_blocks_per_seg;
        resv_count = SM_I(sbi)->reserved_segments << sbi->log_blocks_per_seg;
        ovp_count = SM_I(sbi)->ovp_segments << sbi->log_blocks_per_seg;

        sbi->fggc_threshold = div64_u64((main_count - ovp_count) *
                                BLKS_PER_SEC(sbi), (main_count - resv_count));

        /* give warm/cold data area from slower device */
        if (sbi->s_ndevs && sbi->segs_per_sec == 1)
                SIT_I(sbi)->last_victim[ALLOC_NEXT] =
                                GET_SEGNO(sbi, FDEV(0).end_blk) + 1;
}