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

[Zhiguo Niu]

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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