[PATCH] f2fs: avoid cache writeback busy loop with zero thresholds

[PATCH] f2fs: avoid cache writeback busy loop with zero thresholds

[Wenjie Qi]

When both cache writeback thresholds are zero,
f2fs_should_wake_up_cache_wb() returns true even with no dirty caches.
This makes wait_event_freezable_timeout() return immediately and the
writeback thread busy-loop instead of waiting for its periodic timeout.

Return false when both thresholds are disabled so periodic writeback
can proceed without busy-looping.

Fixes: d7f084b1ad93 ("f2fs: cache: wake up f2fs_writeback when exceeding threshold")
Signed-off-by: Wenjie Qi <qiwenjie@xiaomi.com>
---
Based on f2fs/dev-test at ce439a2b0690.

 fs/f2fs/cache.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/f2fs/cache.c b/fs/f2fs/cache.c
index c76c4660606c5..88d4e479c8469 100644
--- a/fs/f2fs/cache.c
+++ b/fs/f2fs/cache.c
@@ -740,7 +740,8 @@ static inline bool f2fs_should_wake_up_cache_wb(struct f2fs_sb_info *sbi)
 	    nr_dirty < cache_thread->cache_wb_dirty_threshold)
 		return false;
 
-	return true;
+	return cache_thread->cache_wb_total_threshold ||
+		cache_thread->cache_wb_dirty_threshold;
 }
 
 static int f2fs_cache_writeback_kthread(void *data)
-- 
2.43.0

Re: [PATCH] f2fs: avoid cache writeback busy loop with zero thresholds

[Chao Yu]

On 10/9/26 11:53, Wenjie Qi wrote:
> When both cache writeback thresholds are zero,
> f2fs_should_wake_up_cache_wb() returns true even with no dirty caches.
> This makes wait_event_freezable_timeout() return immediately and the
> writeback thread busy-loop instead of waiting for its periodic timeout.
> 
> Return false when both thresholds are disabled so periodic writeback
> can proceed without busy-looping.
> 
> Fixes: d7f084b1ad93 ("f2fs: cache: wake up f2fs_writeback when exceeding threshold")
> Signed-off-by: Wenjie Qi <qiwenjie@xiaomi.com>
> ---
> Based on f2fs/dev-test at ce439a2b0690.
> 
>  fs/f2fs/cache.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/f2fs/cache.c b/fs/f2fs/cache.c
> index c76c4660606c5..88d4e479c8469 100644
> --- a/fs/f2fs/cache.c
> +++ b/fs/f2fs/cache.c
> @@ -740,7 +740,8 @@ static inline bool f2fs_should_wake_up_cache_wb(struct f2fs_sb_info *sbi)
>  	    nr_dirty < cache_thread->cache_wb_dirty_threshold)
>  		return false;
>  
> -	return true;
> +	return cache_thread->cache_wb_total_threshold ||
> +		cache_thread->cache_wb_dirty_threshold;

Thanks for the fix, do you mind I fold this into original patch? as it
is still in dev-test.

Thanks,

>  }
>  
>  static int f2fs_cache_writeback_kthread(void *data)

Re: [PATCH] f2fs: avoid cache writeback busy loop with zero thresholds

[Wenjie Qi]

Hi Chao,

On Fri, Oct 9, 2026, Chao Yu wrote:
> Thanks for the fix, do you mind I fold this into original patch? as it
> is still in dev-test.

Yes, please fold it into the original patch.

Best regards,
Wenjie