Re: [f2fs-dev] [PATCH v7 04/12] f2fs: cache: introduce writeback thread

[Chao Yu]

Zhiguo,

Thanks for the review, let fix them all.

Thanks,

On 9/14/26 17:08, Zhiguo Niu wrote:
> Chao Yu via Linux-f2fs-devel <linux-f2fs-devel@xxxxxxxxxxxxxxxxxxxxx>
> 于2026年9月12日周六 07:28写道：
> > From: Chao Yu <chao@xxxxxxxxxx>
> >
> > This patch introduces a background writeback kthread (f2fs_writeback-x:y)
> > to periodically flush dirty metadata cache entries with a default
> > interval of 5 seconds.
> >
> > It manages thread lifecycle across mount, unmount, and remount (rw/ro)
> > transitions.
> >
> > It introduces a sysfs entry /sys/fs/f2fs/<disk>/cache_wb_interval to control
> > writeback interval.
> >
> > Signed-off-by: Chao Yu <chao@xxxxxxxxxx>
> > ---
> >   Documentation/ABI/testing/sysfs-fs-f2fs |  6 +++
> >   fs/f2fs/cache.c                         | 56 +++++++++++++++++++++++++
> >   fs/f2fs/cache.h                         | 12 ++++++
> >   fs/f2fs/f2fs.h                          |  3 ++
> >   fs/f2fs/super.c                         | 33 ++++++++++++++-
> >   fs/f2fs/sysfs.c                         | 13 +++++-
> >   6 files changed, 120 insertions(+), 3 deletions(-)
> >
> > diff --git a/Documentation/ABI/testing/sysfs-fs-f2fs b/Documentation/ABI/testing/sysfs-fs-f2fs
> > index 0cebc89799dd..d2665b7f1f14 100644
> > --- a/Documentation/ABI/testing/sysfs-fs-f2fs
> > +++ b/Documentation/ABI/testing/sysfs-fs-f2fs
> > @@ -1020,3 +1020,9 @@ Contact:  "Daeho Jeong" <daehojeong@xxxxxxxxxx>
> >   Description:   This is a read-only entry to show the upper bound section number
> >                  for pinned files. Pinned files will only be allocated within
> >                  sections 0 to pinned_area_max_secno - 1.
> > +
> > +What:          /sys/fs/f2fs/<disk>/cache_wb_interval
> > +Date:          August 2026
> > +Contact:       "Chao Yu" <chao@xxxxxxxxxx>
> > +Description:   This is a writable entry to control writeback interval of
> > +               f2fs_writeback-x:y, by default the value is 5000, unit is ms.
> > diff --git a/fs/f2fs/cache.c b/fs/f2fs/cache.c
> > index 563615761d11..404ceac9e6bf 100644
> > --- a/fs/f2fs/cache.c
> > +++ b/fs/f2fs/cache.c
> > @@ -626,3 +626,59 @@ unsigned long f2fs_shrink_cache(struct f2fs_sb_info *sbi,
> >   {
> >          return f2fs_do_shrink_cache(META_CACHE(sbi), nr_to_scan);
> >   }
> > +
> Hi Chao
> > +static int f2fs_cache_writeback_kthread(void *data)
> > +{
> > +       struct f2fs_sb_info *sbi = data;
> > +       struct f2fs_cache_kthread *cache_thread = &sbi->cache_thread;
> > +       wait_queue_head_t *wq = &cache_thread->cache_wb_wq;
> > +       unsigned int interval = cache_thread->cache_wb_interval;
> > +
> > +       set_freezable();
> > +
> > +       while (!kthread_should_stop()) {
> > +               wait_event_freezable_timeout(*wq,
> > +                               kthread_should_stop(),
> > +                               msecs_to_jiffies(interval));
> if wb thread is running and user set cache_wb_interval at the same
> time， the wb thread can not get the new wb interval value for next
> round? because local varible is used here
> > +
> > +               if (kthread_should_stop())
> > +                       break;
> > +               if (f2fs_cp_error(sbi))
> > +                       continue;
> > +       }
> > +       return 0;
> > +}
> > +
> > +int f2fs_start_cache_wb_thread(struct f2fs_sb_info *sbi)
> > +{
> > +       struct f2fs_cache_kthread *cache_thread = &sbi->cache_thread;
> > +       struct task_struct *task;
> > +       dev_t dev = sbi->sb->s_dev;
> > +       char name[36];
> > +
> > +       if (cache_thread->cache_wb_task)
> > +               return 0;
> > +
> > +       init_waitqueue_head(&cache_thread->cache_wb_wq);
> > +       cache_thread->cache_wb_interval = DEF_DIRTY_CACHE_TIMEOUT;
> > +       snprintf(name, sizeof(name), "f2fs_writeback-%u:%u",
> > +                       MAJOR(dev), MINOR(dev));
> > +
> > +       task = kthread_run(f2fs_cache_writeback_kthread, sbi, "%s", name);
> > +       if (IS_ERR(task))
> > +               return PTR_ERR(task);
> > +
> > +       cache_thread->cache_wb_task = task;
> > +       return 0;
> > +}
> > +
> > +void f2fs_stop_cache_wb_thread(struct f2fs_sb_info *sbi)
> > +{
> > +       struct f2fs_cache_kthread *cache_thread = &sbi->cache_thread;
> > +
> > +       if (!cache_thread->cache_wb_task)
> > +               return;
> > +
> > +       kthread_stop(cache_thread->cache_wb_task);
> > +       cache_thread->cache_wb_task = NULL;
> > +}
> > diff --git a/fs/f2fs/cache.h b/fs/f2fs/cache.h
> > index 5728e2225465..ea0cf9adf194 100644
> > --- a/fs/f2fs/cache.h
> > +++ b/fs/f2fs/cache.h
> > @@ -209,4 +209,16 @@ void f2fs_stop_cache_wb_thread(struct f2fs_sb_info *sbi);
> >   unsigned long f2fs_shrink_cache(struct f2fs_sb_info *sbi,
> >                                  unsigned long nr_to_scan);
> >
> > +#define DEF_DIRTY_CACHE_TIMEOUT 5000
> > +
> > +struct f2fs_cache_kthread {
> > +       struct task_struct *cache_wb_task;
> > +       wait_queue_head_t cache_wb_wq;
> > +       atomic_t cache_wb_trigger;
> not used?
> thanks!
> > +       unsigned int cache_wb_interval;
> > +};
> > +
> > +int f2fs_start_cache_wb_thread(struct f2fs_sb_info *sbi);
> > +void f2fs_stop_cache_wb_thread(struct f2fs_sb_info *sbi);
> > +
> >   #endif /* _LINUX_F2FS_CACHE_H */
> > diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> > index 85c4bf40b4aa..c0f82b63d732 100644
> > --- a/fs/f2fs/f2fs.h
> > +++ b/fs/f2fs/f2fs.h
> > @@ -2110,6 +2110,9 @@ struct f2fs_sb_info {
> >
> >          /* f2fs internal cache */
> >          struct f2fs_cached_block_list meta_blocks;
> > +
> > +       /* internal cache flush thread */
> > +       struct f2fs_cache_kthread cache_thread;
> >   };
> >
> >   /* Definitions to access f2fs_sb_info */
> > diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
> > index b731b9bb7b54..516b4ee12564 100644
> > --- a/fs/f2fs/super.c
> > +++ b/fs/f2fs/super.c
> > @@ -2039,6 +2039,7 @@ static void f2fs_put_super(struct super_block *sb)
> >           * flush all issued checkpoints and stop checkpoint issue thread.
> >           * after then, all checkpoints should be done by each process context.
> >           */
> > +       f2fs_stop_cache_wb_thread(sbi);
> >          f2fs_stop_ckpt_thread(sbi);
> >
> >          /*
> > @@ -2845,6 +2846,7 @@ static int __f2fs_remount(struct fs_context *fc, struct super_block *sb)
> >          unsigned int flags = fc->sb_flags;
> >          int err;
> >          bool need_restart_gc = false, need_stop_gc = false;
> > +       bool need_restart_wb = false, need_stop_wb = false;
> >          bool need_restart_flush = false, need_stop_flush = false;
> >          bool need_restart_discard = false, need_stop_discard = false;
> >          bool need_enable_checkpoint = false, need_disable_checkpoint = false;
> > @@ -3004,6 +3006,18 @@ static int __f2fs_remount(struct fs_context *fc, struct super_block *sb)
> >                  need_stop_gc = true;
> >          }
> >
> > +       if (flags & SB_RDONLY) {
> > +               if (sbi->cache_thread.cache_wb_task) {
> > +                       f2fs_stop_cache_wb_thread(sbi);
> > +                       need_restart_wb = true;
> > +               }
> > +       } else if (!sbi->cache_thread.cache_wb_task) {
> > +               err = f2fs_start_cache_wb_thread(sbi);
> > +               if (err)
> > +                       goto restore_gc;
> > +               need_stop_wb = true;
> > +       }
> > +
> >          if (flags & SB_RDONLY) {
> >                  sync_inodes_sb(sb);
> >
> > @@ -3011,7 +3025,7 @@ static int __f2fs_remount(struct fs_context *fc, struct super_block *sb)
> >                  set_sbi_flag(sbi, SBI_IS_CLOSE);
> >                  err = f2fs_sync_fs(sb, 1);
> >                  if (err)
> > -                       goto restore_gc;
> > +                       goto restore_wb;
> >                  clear_sbi_flag(sbi, SBI_IS_CLOSE);
> >          }
> >
> > @@ -3026,7 +3040,7 @@ static int __f2fs_remount(struct fs_context *fc, struct super_block *sb)
> >          } else {
> >                  err = f2fs_create_flush_cmd_control(sbi);
> >                  if (err)
> > -                       goto restore_gc;
> > +                       goto restore_wb;
> >                  need_stop_flush = true;
> >          }
> >
> > @@ -3123,6 +3137,13 @@ static int __f2fs_remount(struct fs_context *fc, struct super_block *sb)
> >                  clear_opt(sbi, FLUSH_MERGE);
> >                  f2fs_destroy_flush_cmd_control(sbi, false);
> >          }
> > +restore_wb:
> > +       if (need_restart_wb) {
> > +               if (f2fs_start_cache_wb_thread(sbi))
> > +                       f2fs_warn(sbi, "background cache writeback thread has stopped");
> > +       } else if (need_stop_wb) {
> > +               f2fs_stop_cache_wb_thread(sbi);
> > +       }
> >   restore_gc:
> >          if (need_restart_gc) {
> >                  if (f2fs_start_gc_thread(sbi))
> > @@ -5529,6 +5550,12 @@ static int f2fs_fill_super(struct super_block *sb, struct fs_context *fc)
> >                          goto sync_free_meta;
> >          }
> >
> > +       if (!f2fs_readonly(sb)) {
> > +               err = f2fs_start_cache_wb_thread(sbi);
> > +               if (err)
> > +                       goto stop_gc_thread;
> > +       }
> > +
> >          /* recover broken superblock */
> >          if (recovery) {
> >                  err = f2fs_commit_super(sbi, true);
> > @@ -5551,6 +5578,8 @@ static int f2fs_fill_super(struct super_block *sb, struct fs_context *fc)
> >          sbi->umount_lock_holder = NULL;
> >          return 0;
> >
> > +stop_gc_thread:
> > +       f2fs_stop_gc_thread(sbi);
> >   sync_free_meta:
> >          /* safe to flush all the data */
> >          sync_filesystem(sbi->sb);
> > diff --git a/fs/f2fs/sysfs.c b/fs/f2fs/sysfs.c
> > index aaca9ed9b169..ad25733e32c0 100644
> > --- a/fs/f2fs/sysfs.c
> > +++ b/fs/f2fs/sysfs.c
> > @@ -40,6 +40,7 @@ enum {
> >          RESERVED_BLOCKS,        /* struct f2fs_sb_info */
> >          CPRC_INFO,      /* struct ckpt_req_control */
> >          ATGC_INFO,      /* struct atgc_management */
> > +       WB_THREAD,      /* struct f2fs_cache_kthread */
> >   };
> >
> >   static const char *gc_mode_names[MAX_GC_MODE] = {
> > @@ -98,6 +99,8 @@ static unsigned char *__struct_ptr(struct f2fs_sb_info *sbi, int struct_type)
> >                  return (unsigned char *)&sbi->cprc_info;
> >          else if (struct_type == ATGC_INFO)
> >                  return (unsigned char *)&sbi->am;
> > +       else if (struct_type == WB_THREAD)
> > +               return (unsigned char *)&sbi->cache_thread;
> >          return NULL;
> >   }
> >
> > @@ -1008,7 +1011,8 @@ static ssize_t f2fs_sbi_store(struct f2fs_attr *a,
> >          bool gc_entry = (!strcmp(a->attr.name, "gc_urgent") ||
> >                                          a->struct_type == GC_THREAD);
> >          bool thread_entry = !strcmp(a->attr.name, "ckpt_thread_ioprio") ||
> > -                       !strcmp(a->attr.name, "critical_task_priority");
> > +                       !strcmp(a->attr.name, "critical_task_priority") ||
> > +                       !strcmp(a->attr.name, "cache_wb_interval");
> >
> >          if (gc_entry || thread_entry) {
> >                  if (!down_read_trylock(&sbi->sb->s_umount))
> > @@ -1218,6 +1222,9 @@ static struct f2fs_attr f2fs_attr_##name = __ATTR(name, 0444, name##_show, NULL)
> >   #define ATGC_INFO_RW_ATTR(name, elname)                                \
> >          F2FS_RW_ATTR(ATGC_INFO, atgc_management, name, elname)
> >
> > +#define WB_THREAD_RW_ATTR(name, elname)                                \
> > +       F2FS_RW_ATTR(WB_THREAD, f2fs_cache_kthread, name, elname)
> > +
> >   /* GC_THREAD ATTR */
> >   GC_THREAD_RW_ATTR(gc_urgent_sleep_time, urgent_sleep_time);
> >   GC_THREAD_RW_ATTR(gc_min_sleep_time, min_sleep_time);
> > @@ -1347,6 +1354,9 @@ ATGC_INFO_RW_ATTR(atgc_candidate_count, max_candidate_count);
> >   ATGC_INFO_RW_ATTR(atgc_age_weight, age_weight);
> >   ATGC_INFO_RW_ATTR(atgc_age_threshold, age_threshold);
> >
> > +/* WB_THREAD ATTR */
> > +WB_THREAD_RW_ATTR(cache_wb_interval, cache_wb_interval);
> > +
> >   F2FS_GENERAL_RO_ATTR(dirty_segments);
> >   F2FS_GENERAL_RO_ATTR(free_segments);
> >   F2FS_GENERAL_RO_ATTR(ovp_segments);
> > @@ -1533,6 +1543,7 @@ static struct attribute *f2fs_attrs[] = {
> >          ATTR_LIST(lock_duration_priority),
> >          ATTR_LIST(adjust_lock_priority),
> >          ATTR_LIST(critical_task_priority),
> > +       ATTR_LIST(cache_wb_interval),
> >          NULL,
> >   };
> >   ATTRIBUTE_GROUPS(f2fs);
> > --
> > 2.49.0
> >
> >
> >
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