Message-ID: <CACOAw_wpjcdEp29H7zBgVbBZPBT55PKwX76RmfkcRjMTnpGosA@mail.gmail.com>
Date:   Fri, 15 Jan 2021 23:23:04 +0900
From:   Daeho Jeong <daeho43@...il.com>
To:     Chao Yu <yuchao0@...wei.com>
Cc:     linux-kernel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net, kernel-team@...roid.com,
        Sungjong Seo <sj1557.seo@...sung.com>,
        Daeho Jeong <daehojeong@...gle.com>
Subject: Re: [f2fs-dev] [PATCH v2 1/2] f2fs: introduce checkpoint=merge mount option

2021년 1월 15일 (금) 오후 11:00, Daeho Jeong <daeho43@...il.com>님이 작성:
>
> 2021년 1월 15일 (금) 오후 6:22, Chao Yu <yuchao0@...wei.com>님이 작성:
> >
> > On 2021/1/14 14:23, Daeho Jeong wrote:
> > > From: Daeho Jeong <daehojeong@...gle.com>
> > >
> > > We've added a new mount option "checkpoint=merge", which creates a
> > > kernel daemon and makes it to merge concurrent checkpoint requests as
> > > much as possible to eliminate redundant checkpoint issues. Plus, we
> > > can eliminate the sluggish issue caused by slow checkpoint operation
> > > when the checkpoint is done in a process context in a cgroup having
> > > low i/o budget and cpu shares, and The below verification result
> > > explains this.
> > > The basic idea has come from https://opensource.samsung.com.
> > >
> > > [Verification]
> > > Android Pixel Device(ARM64, 7GB RAM, 256GB UFS)
> > > Create two I/O cgroups (fg w/ weight 100, bg w/ wight 20)
> > > Set "strict_guarantees" to "1" in BFQ tunables
> > >
> > > In "fg" cgroup,
> > > - thread A => trigger 1000 checkpoint operations
> > >    "for i in `seq 1 1000`; do touch test_dir1/file; fsync test_dir1;
> > >     done"
> > > - thread B => gererating async. I/O
> > >    "fio --rw=write --numjobs=1 --bs=128k --runtime=3600 --time_based=1
> > >         --filename=test_img --name=test"
> > >
> > > In "bg" cgroup,
> > > - thread C => trigger repeated checkpoint operations
> > >    "echo $$ > /dev/blkio/bg/tasks; while true; do touch test_dir2/file;
> > >     fsync test_dir2; done"
> > >
> > > We've measured thread A's execution time.
> > >
> > > [ w/o patch ]
> > > Elapsed Time: Avg. 68 seconds
> > > [ w/  patch ]
> > > Elapsed Time: Avg. 48 seconds
> > >
> > > Signed-off-by: Daeho Jeong <daehojeong@...gle.com>
> > > Signed-off-by: Sungjong Seo <sj1557.seo@...sung.com>
> > > ---
> > > v2:
> > > - inlined ckpt_req_control into f2fs_sb_info and collected stastics
> > >    of checkpoint merge operations
> > > ---
> > >   Documentation/filesystems/f2fs.rst |   6 ++
> > >   fs/f2fs/checkpoint.c               | 163 +++++++++++++++++++++++++++++
> > >   fs/f2fs/debug.c                    |  12 +++
> > >   fs/f2fs/f2fs.h                     |  27 +++++
> > >   fs/f2fs/super.c                    |  56 +++++++++-
> > >   5 files changed, 260 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/Documentation/filesystems/f2fs.rst b/Documentation/filesystems/f2fs.rst
> > > index dae15c96e659..bccc021bf31a 100644
> > > --- a/Documentation/filesystems/f2fs.rst
> > > +++ b/Documentation/filesystems/f2fs.rst
> > > @@ -247,6 +247,12 @@ checkpoint=%s[:%u[%]]     Set to "disable" to turn off checkpointing. Set to "enabl
> > >                        hide up to all remaining free space. The actual space that
> > >                        would be unusable can be viewed at /sys/fs/f2fs/<disk>/unusable
> > >                        This space is reclaimed once checkpoint=enable.
> > > +                      Here is another option "merge", which creates a kernel daemon
> > > +                      and makes it to merge concurrent checkpoint requests as much
> > > +                      as possible to eliminate redundant checkpoint issues. Plus,
> > > +                      we can eliminate the sluggish issue caused by slow checkpoint
> > > +                      operation when the checkpoint is done in a process context in
> > > +                      a cgroup having low i/o budget and cpu shares.
> > >   compress_algorithm=%s        Control compress algorithm, currently f2fs supports "lzo",
> > >                        "lz4", "zstd" and "lzo-rle" algorithm.
> > >   compress_log_size=%u         Support configuring compress cluster size, the size will
> > > diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
> > > index 897edb7c951a..e0668cec3b80 100644
> > > --- a/fs/f2fs/checkpoint.c
> > > +++ b/fs/f2fs/checkpoint.c
> > > @@ -13,6 +13,7 @@
> > >   #include <linux/f2fs_fs.h>
> > >   #include <linux/pagevec.h>
> > >   #include <linux/swap.h>
> > > +#include <linux/kthread.h>
> > >
> > >   #include "f2fs.h"
> > >   #include "node.h"
> > > @@ -20,6 +21,8 @@
> > >   #include "trace.h"
> > >   #include <trace/events/f2fs.h>
> > >
> > > +#define DEFAULT_CHECKPOINT_IOPRIO (IOPRIO_PRIO_VALUE(IOPRIO_CLASS_BE, 3))
> > > +
> > >   static struct kmem_cache *ino_entry_slab;
> > >   struct kmem_cache *f2fs_inode_entry_slab;
> > >
> > > @@ -1707,3 +1710,163 @@ void f2fs_destroy_checkpoint_caches(void)
> > >       kmem_cache_destroy(ino_entry_slab);
> > >       kmem_cache_destroy(f2fs_inode_entry_slab);
> > >   }
> > > +
> > > +static int __write_checkpoint_sync(struct f2fs_sb_info *sbi)
> > > +{
> > > +     struct cp_control cpc = { .reason = CP_SYNC, };
> > > +     int err;
> > > +
> > > +     down_write(&sbi->gc_lock);
> > > +     err = f2fs_write_checkpoint(sbi, &cpc);
> > > +     up_write(&sbi->gc_lock);
> > > +
> > > +     return err;
> > > +}
> > > +
> > > +static void __checkpoint_and_complete_reqs(struct f2fs_sb_info *sbi)
> > > +{
> > > +     struct ckpt_req_control *cprc = &sbi->cprc_info;
> > > +     struct ckpt_req *req, *next;
> > > +     struct llist_node *dispatch_list;
> > > +     u64 sum_diff = 0, diff, count = 0;
> > > +     int ret;
> > > +
> > > +     dispatch_list = llist_del_all(&cprc->issue_list);
> > > +     if (!dispatch_list)
> > > +             return;
> > > +     dispatch_list = llist_reverse_order(dispatch_list);
> > > +
> > > +     ret = __write_checkpoint_sync(sbi);
> > > +     atomic_inc(&cprc->issued_ckpt);
> > > +
> > > +     llist_for_each_entry_safe(req, next, dispatch_list, llnode) {
> > > +             atomic_dec(&cprc->queued_ckpt);
> > > +             atomic_inc(&cprc->total_ckpt);
> > > +             diff = (u64)ktime_ms_delta(ktime_get(), req->queue_time);
> > > +             req->ret = ret;
> > > +             complete(&req->wait);
> > > +
> > > +             sum_diff += diff;
> > > +             count++;
> > > +     }
> >
> > How about updating queued_ckpt and total_ckpt in batch, update atomic
> > variable one by one is low efficient.
> >
>
> You mean like using spin_lock()?
>

Ah, you mean like updating these values as much as the count of the
loop at once?

> > > +
> > > +     spin_lock(&cprc->stat_lock);
> > > +     cprc->cur_time = (unsigned int)div64_u64(sum_diff, count);
> >
> > ktime_get() returns time based ns unit, in extreme scenario, average
> > time cp cost will overflow 32-bit variable, I doubt.
> >
>
> sum_diff is already turned into msec using ktime_ms_delta() above.
>
> > > +     if (cprc->peak_time < cprc->cur_time)
> > > +             cprc->peak_time = cprc->cur_time;
> > > +     spin_unlock(&cprc->stat_lock);
> > > +}
> > > +
> > > +static int issue_checkpoint_thread(void *data)
> > > +{
> > > +     struct f2fs_sb_info *sbi = data;
> > > +     struct ckpt_req_control *cprc = &sbi->cprc_info;
> > > +     wait_queue_head_t *q = &cprc->ckpt_wait_queue;
> > > +repeat:
> > > +     if (kthread_should_stop())
> > > +             return 0;
> > > +
> > > +     sb_start_intwrite(sbi->sb);
> > > +
> > > +     if (!llist_empty(&cprc->issue_list))
> > > +             __checkpoint_and_complete_reqs(sbi);
> > > +
> > > +     sb_end_intwrite(sbi->sb);
> > > +
> > > +     wait_event_interruptible(*q,
> > > +             kthread_should_stop() || !llist_empty(&cprc->issue_list));
> > > +     goto repeat;
> > > +}
> > > +
> > > +static void flush_remained_ckpt_reqs(struct f2fs_sb_info *sbi,
> > > +             struct ckpt_req *wait_req)
> > > +{
> > > +     struct ckpt_req_control *cprc = &sbi->cprc_info;
> > > +
> > > +     if (!llist_empty(&cprc->issue_list)) {
> > > +             __checkpoint_and_complete_reqs(sbi);
> > > +     } else {
> > > +             /* already dispatched by issue_checkpoint_thread */
> > > +             if (wait_req)
> > > +                     wait_for_completion(&wait_req->wait);
> > > +     }
> > > +}
> > > +
> > > +static void init_ckpt_req(struct ckpt_req *req)
> > > +{
> > > +     memset(req, 0, sizeof(struct ckpt_req));
> > > +
> > > +     init_completion(&req->wait);
> > > +     req->queue_time = ktime_get();
> > > +}
> > > +
> > > +int f2fs_issue_checkpoint(struct f2fs_sb_info *sbi)
> > > +{
> > > +     struct ckpt_req_control *cprc = &sbi->cprc_info;
> > > +     struct ckpt_req req;
> > > +
> > > +     if (!cprc || !cprc->f2fs_issue_ckpt)
> >
> > !cprc check is unneeded now.
> >
>
> Got it~
>
> > > +             return __write_checkpoint_sync(sbi);
> > > +
> > > +     init_ckpt_req(&req);
> > > +
> > > +     llist_add(&req.llnode, &cprc->issue_list);
> > > +     atomic_inc(&cprc->queued_ckpt);
> > > +
> > > +     /* update issue_list before we wake up issue_checkpoint thread */
> > > +     smp_mb();
> > > +
> > > +     if (waitqueue_active(&cprc->ckpt_wait_queue))
> > > +             wake_up(&cprc->ckpt_wait_queue);
> > > +
> > > +     if (cprc->f2fs_issue_ckpt)
> > > +             wait_for_completion(&req.wait);
> > > +     else
> > > +             flush_remained_ckpt_reqs(sbi, &req);
> > > +
> > > +     return req.ret;
> > > +}
> > > +
> > > +int f2fs_start_ckpt_thread(struct f2fs_sb_info *sbi)
> > > +{
> > > +     dev_t dev = sbi->sb->s_bdev->bd_dev;
> > > +     struct ckpt_req_control *cprc = &sbi->cprc_info;
> > > +
> > > +     if (cprc->f2fs_issue_ckpt)
> > > +             return 0;
> >
> >          ^^^^^ here
> >
>
> ditto
>
> > > +
> > > +     cprc->f2fs_issue_ckpt = kthread_run(issue_checkpoint_thread, sbi,
> > > +                     "f2fs_ckpt-%u:%u", MAJOR(dev), MINOR(dev));
> > > +     if (IS_ERR(cprc->f2fs_issue_ckpt))
> >
> > we should assign cprc->f2fs_issue_ckpt to NULL, this will more safer than
> > keeping old error value left in this variable, to avoid checking the wrong
> > value as in above position.
> >
>
> ditto
>
> > > +             return PTR_ERR(cprc->f2fs_issue_ckpt);
> > > +
> > > +     set_task_ioprio(cprc->f2fs_issue_ckpt, DEFAULT_CHECKPOINT_IOPRIO);
> > > +
> > > +     return 0;
> > > +}
> > > +
> > > +void f2fs_stop_ckpt_thread(struct f2fs_sb_info *sbi)
> > > +{
> > > +     struct ckpt_req_control *cprc = &sbi->cprc_info;
> > > +
> > > +     if (cprc->f2fs_issue_ckpt) {
> > > +             struct task_struct *ckpt_task = cprc->f2fs_issue_ckpt;
> > > +
> > > +             cprc->f2fs_issue_ckpt = NULL;
> > > +             kthread_stop(ckpt_task);
> > > +
> > > +             flush_remained_ckpt_reqs(sbi, NULL);
> > > +     }
> > > +}
> > > +
> > > +void f2fs_init_ckpt_req_control(struct f2fs_sb_info *sbi)
> > > +{
> > > +     struct ckpt_req_control *cprc = &sbi->cprc_info;
> > > +
> > > +     atomic_set(&cprc->issued_ckpt, 0);
> > > +     atomic_set(&cprc->total_ckpt, 0);
> > > +     atomic_set(&cprc->queued_ckpt, 0);
> > > +     init_waitqueue_head(&cprc->ckpt_wait_queue);
> > > +     init_llist_head(&cprc->issue_list);
> > > +     spin_lock_init(&cprc->stat_lock);
> > > +}
> > > diff --git a/fs/f2fs/debug.c b/fs/f2fs/debug.c
> > > index 197c914119da..91855d5721cd 100644
> > > --- a/fs/f2fs/debug.c
> > > +++ b/fs/f2fs/debug.c
> > > @@ -120,6 +120,13 @@ static void update_general_status(struct f2fs_sb_info *sbi)
> > >                       atomic_read(&SM_I(sbi)->dcc_info->discard_cmd_cnt);
> > >               si->undiscard_blks = SM_I(sbi)->dcc_info->undiscard_blks;
> > >       }
> > > +     si->nr_issued_ckpt = atomic_read(&sbi->cprc_info.issued_ckpt);
> > > +     si->nr_total_ckpt = atomic_read(&sbi->cprc_info.total_ckpt);
> > > +     si->nr_queued_ckpt = atomic_read(&sbi->cprc_info.queued_ckpt);
> > > +     spin_lock(&sbi->cprc_info.stat_lock);
> > > +     si->cur_ckpt_time = sbi->cprc_info.cur_time;
> > > +     si->peak_ckpt_time = sbi->cprc_info.peak_time;
> > > +     spin_unlock(&sbi->cprc_info.stat_lock);
> > >       si->total_count = (int)sbi->user_block_count / sbi->blocks_per_seg;
> > >       si->rsvd_segs = reserved_segments(sbi);
> > >       si->overp_segs = overprovision_segments(sbi);
> > > @@ -417,6 +424,11 @@ static int stat_show(struct seq_file *s, void *v)
> > >                               si->meta_count[META_NAT]);
> > >               seq_printf(s, "  - ssa blocks : %u\n",
> > >                               si->meta_count[META_SSA]);
> > > +             seq_printf(s, "CP merge (Queued: %4d, Issued: %4d, Total: %4d, "
> > > +                             "Cur time: %4d(ms), Peak time: %4d(ms))\n",
> > > +                             si->nr_queued_ckpt, si->nr_issued_ckpt,
> > > +                             si->nr_total_ckpt, si->cur_ckpt_time,
> > > +                             si->peak_ckpt_time);
> > >               seq_printf(s, "GC calls: %d (BG: %d)\n",
> > >                          si->call_count, si->bg_gc);
> > >               seq_printf(s, "  - data segments : %d (%d)\n",
> > > diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> > > index bb11759191dc..f2ae075aa723 100644
> > > --- a/fs/f2fs/f2fs.h
> > > +++ b/fs/f2fs/f2fs.h
> > > @@ -97,6 +97,7 @@ extern const char *f2fs_fault_name[FAULT_MAX];
> > >   #define F2FS_MOUNT_DISABLE_CHECKPOINT       0x02000000
> > >   #define F2FS_MOUNT_NORECOVERY               0x04000000
> > >   #define F2FS_MOUNT_ATGC                     0x08000000
> > > +#define F2FS_MOUNT_MERGE_CHECKPOINT  0x10000000
> > >
> > >   #define F2FS_OPTION(sbi)    ((sbi)->mount_opt)
> > >   #define clear_opt(sbi, option)      (F2FS_OPTION(sbi).opt &= ~F2FS_MOUNT_##option)
> > > @@ -266,6 +267,25 @@ struct fsync_node_entry {
> > >       unsigned int seq_id;    /* sequence id */
> > >   };
> > >
> > > +struct ckpt_req {
> > > +     struct completion wait;         /* completion for checkpoint done */
> > > +     struct llist_node llnode;       /* llist_node to be linked in wait queue */
> > > +     int ret;                        /* return code of checkpoint */
> > > +     ktime_t queue_time;             /* request queued time */
> > > +};
> > > +
> > > +struct ckpt_req_control {
> > > +     struct task_struct *f2fs_issue_ckpt;    /* checkpoint task */
> > > +     wait_queue_head_t ckpt_wait_queue;      /* waiting queue for wake-up */
> > > +     atomic_t issued_ckpt;           /* # of actually issued ckpts */
> > > +     atomic_t total_ckpt;            /* # of total ckpts */
> > > +     atomic_t queued_ckpt;           /* # of queued ckpts */
> > > +     struct llist_head issue_list;   /* list for command issue */
> > > +     spinlock_t stat_lock;           /* lock for below checkpoint time stats */
> > > +     unsigned int cur_time;          /* cur wait time in msec for currently issued checkpoint */
> > > +     unsigned int peak_time;         /* peak wait time in msec until now */
> > > +};
> > > +
> > >   /* for the bitmap indicate blocks to be discarded */
> > >   struct discard_entry {
> > >       struct list_head list;  /* list head */
> > > @@ -1404,6 +1424,7 @@ struct f2fs_sb_info {
> > >       wait_queue_head_t cp_wait;
> > >       unsigned long last_time[MAX_TIME];      /* to store time in jiffies */
> > >       long interval_time[MAX_TIME];           /* to store thresholds */
> > > +     struct ckpt_req_control cprc_info;      /* for checkpoint request control */
> > >
> > >       struct inode_management im[MAX_INO_ENTRY];      /* manage inode cache */
> > >
> > > @@ -3418,6 +3439,10 @@ int f2fs_write_checkpoint(struct f2fs_sb_info *sbi, struct cp_control *cpc);
> > >   void f2fs_init_ino_entry_info(struct f2fs_sb_info *sbi);
> > >   int __init f2fs_create_checkpoint_caches(void);
> > >   void f2fs_destroy_checkpoint_caches(void);
> > > +int f2fs_issue_checkpoint(struct f2fs_sb_info *sbi);
> > > +int f2fs_start_ckpt_thread(struct f2fs_sb_info *sbi);
> > > +void f2fs_stop_ckpt_thread(struct f2fs_sb_info *sbi);
> > > +void f2fs_init_ckpt_req_control(struct f2fs_sb_info *sbi);
> > >
> > >   /*
> > >    * data.c
> > > @@ -3530,6 +3555,8 @@ struct f2fs_stat_info {
> > >       int nr_discarding, nr_discarded;
> > >       int nr_discard_cmd;
> > >       unsigned int undiscard_blks;
> > > +     int nr_issued_ckpt, nr_total_ckpt, nr_queued_ckpt;
> > > +     unsigned int cur_ckpt_time, peak_ckpt_time;
> > >       int inline_xattr, inline_inode, inline_dir, append, update, orphans;
> > >       int compr_inode;
> > >       unsigned long long compr_blocks;
> > > diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
> > > index b4a07fe62d1a..1c1771be8a16 100644
> > > --- a/fs/f2fs/super.c
> > > +++ b/fs/f2fs/super.c
> > > @@ -143,6 +143,7 @@ enum {
> > >       Opt_checkpoint_disable_cap,
> > >       Opt_checkpoint_disable_cap_perc,
> > >       Opt_checkpoint_enable,
> > > +     Opt_checkpoint_merge,
> > >       Opt_compress_algorithm,
> > >       Opt_compress_log_size,
> > >       Opt_compress_extension,
> > > @@ -213,6 +214,7 @@ static match_table_t f2fs_tokens = {
> > >       {Opt_checkpoint_disable_cap, "checkpoint=disable:%u"},
> > >       {Opt_checkpoint_disable_cap_perc, "checkpoint=disable:%u%%"},
> > >       {Opt_checkpoint_enable, "checkpoint=enable"},
> > > +     {Opt_checkpoint_merge, "checkpoint=merge"},
> > >       {Opt_compress_algorithm, "compress_algorithm=%s"},
> > >       {Opt_compress_log_size, "compress_log_size=%u"},
> > >       {Opt_compress_extension, "compress_extension=%s"},
> > > @@ -872,6 +874,9 @@ static int parse_options(struct super_block *sb, char *options, bool is_remount)
> > >               case Opt_checkpoint_enable:
> > >                       clear_opt(sbi, DISABLE_CHECKPOINT);
> > >                       break;
> > > +             case Opt_checkpoint_merge:
> > > +                     set_opt(sbi, MERGE_CHECKPOINT);
> > > +                     break;
> > >   #ifdef CONFIG_F2FS_FS_COMPRESSION
> > >               case Opt_compress_algorithm:
> > >                       if (!f2fs_sb_has_compression(sbi)) {
> > > @@ -1040,6 +1045,12 @@ static int parse_options(struct super_block *sb, char *options, bool is_remount)
> > >               return -EINVAL;
> > >       }
> > >
> > > +     if (test_opt(sbi, DISABLE_CHECKPOINT) &&
> > > +                     test_opt(sbi, MERGE_CHECKPOINT)) {
> > > +             f2fs_err(sbi, "checkpoint=merge cannot be used with checkpoint=disable\n");
> > > +             return -EINVAL;
> > > +     }
> > > +
> > >       /* Not pass down write hints if the number of active logs is lesser
> > >        * than NR_CURSEG_PERSIST_TYPE.
> > >        */
> > > @@ -1245,6 +1256,12 @@ static void f2fs_put_super(struct super_block *sb)
> > >       /* prevent remaining shrinker jobs */
> > >       mutex_lock(&sbi->umount_mutex);
> > >
> > > +     /*
> > > +      * flush all issued checkpoints and stop checkpoint issue thread.
> > > +      * after then, all checkpoints should be done by each process context.
> > > +      */
> > > +     f2fs_stop_ckpt_thread(sbi);
> > > +
> > >       /*
> > >        * We don't need to do checkpoint when superblock is clean.
> > >        * But, the previous checkpoint was not done by umount, it needs to do
> > > @@ -1347,10 +1364,13 @@ int f2fs_sync_fs(struct super_block *sb, int sync)
> > >               struct cp_control cpc;
> > >
> > >               cpc.reason = __get_cp_reason(sbi);
> > > -
> > > -             down_write(&sbi->gc_lock);
> > > -             err = f2fs_write_checkpoint(sbi, &cpc);
> > > -             up_write(&sbi->gc_lock);
> > > +             if (test_opt(sbi, MERGE_CHECKPOINT) && cpc.reason == CP_SYNC) {
> > > +                     err = f2fs_issue_checkpoint(sbi);
> > > +             } else {
> > > +                     down_write(&sbi->gc_lock);
> > > +                     err = f2fs_write_checkpoint(sbi, &cpc);
> > > +                     up_write(&sbi->gc_lock);
> > > +             }
> >
> > Why not merging above logic into f2fs_issue_checkpoint(), so here, we can just
> > call f2fs_issue_checkpoint(), then the code would be more clean here.
> >
> > Thanks,
> >
>
> Sure~
>
> > >       }
> > >       f2fs_trace_ios(NULL, 1);
> > >
> > > @@ -1674,6 +1694,8 @@ static int f2fs_show_options(struct seq_file *seq, struct dentry *root)
> > >       if (test_opt(sbi, DISABLE_CHECKPOINT))
> > >               seq_printf(seq, ",checkpoint=disable:%u",
> > >                               F2FS_OPTION(sbi).unusable_cap);
> > > +     if (test_opt(sbi, MERGE_CHECKPOINT))
> > > +             seq_puts(seq, ",checkpoint=merge");
> > >       if (F2FS_OPTION(sbi).fsync_mode == FSYNC_MODE_POSIX)
> > >               seq_printf(seq, ",fsync_mode=%s", "posix");
> > >       else if (F2FS_OPTION(sbi).fsync_mode == FSYNC_MODE_STRICT)
> > > @@ -1954,6 +1976,18 @@ static int f2fs_remount(struct super_block *sb, int *flags, char *data)
> > >               }
> > >       }
> > >
> > > +     if (!test_opt(sbi, MERGE_CHECKPOINT)) {
> > > +             f2fs_stop_ckpt_thread(sbi);
> > > +     } else {
> > > +             err = f2fs_start_ckpt_thread(sbi);
> > > +             if (err) {
> > > +                     f2fs_err(sbi,
> > > +                         "Failed to start F2FS issue_checkpoint_thread (%d)",
> > > +                         err);
> > > +                     goto restore_gc;
> > > +             }
> > > +     }
> > > +
> > >       /*
> > >        * We stop issue flush thread if FS is mounted as RO
> > >        * or if flush_merge is not passed in mount option.
> > > @@ -3701,6 +3735,18 @@ static int f2fs_fill_super(struct super_block *sb, void *data, int silent)
> > >
> > >       f2fs_init_fsync_node_info(sbi);
> > >
> > > +     /* setup checkpoint request control and start checkpoint issue thread */
> > > +     f2fs_init_ckpt_req_control(sbi);
> > > +     if (test_opt(sbi, MERGE_CHECKPOINT)) {
> > > +             err = f2fs_start_ckpt_thread(sbi);
> > > +             if (err) {
> > > +                     f2fs_err(sbi,
> > > +                         "Failed to start F2FS issue_checkpoint_thread (%d)",
> > > +                         err);
> > > +                     goto stop_ckpt_thread;
> > > +             }
> > > +     }
> > > +
> > >       /* setup f2fs internal modules */
> > >       err = f2fs_build_segment_manager(sbi);
> > >       if (err) {
> > > @@ -3910,6 +3956,8 @@ static int f2fs_fill_super(struct super_block *sb, void *data, int silent)
> > >   free_sm:
> > >       f2fs_destroy_segment_manager(sbi);
> > >       f2fs_destroy_post_read_wq(sbi);
> > > +stop_ckpt_thread:
> > > +     f2fs_stop_ckpt_thread(sbi);
> > >   free_devices:
> > >       destroy_device_list(sbi);
> > >       kvfree(sbi->ckpt);
> > >

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