Re: [f2fs-dev] [PATCH v2 3/3] f2fs: optimize NAT block loading during checkpoint write

[Chao Yu via Linux-f2fs-devel <linux-f2fs-devel@lists.sourceforge.net>]

On 1/13/2026 11:23 PM, Yongpeng Yang wrote:
> From: Yongpeng Yang <yangyongpeng@xiaomi.com>
> 
> Under stress tests with frequent metadata operations, checkpoint write
> time can become excessively long. Analysis shows that the slowdown is
> caused by synchronous, one-by-one reads of NAT blocks during checkpoint
> processing.
> 
> The issue can be reproduced with the following workload:
> 1. seq 1 650000 | xargs -P 16 -n 1 touch
> 2. sync # avoid checkpoint write during deleting
> 3. delete 1 file every 455 files
> 4. echo 3 > /proc/sys/vm/drop_caches
> 5. sync # trigger checkpoint write
> 
> This patch submits read I/O for all NAT blocks required in the
> __flush_nat_entry_set() phase in advance, reducing the overhead of
> synchronous waiting for individual NAT block reads.
> 
> The NAT block flush latency before and after the change is as below:
> 
> |             |NAT blocks accessed|NAT blocks read|Flush time (ms)|
> |-------------|-------------------|---------------|---------------|
> |Before change|1205               |1191           |158            |
> |After change |1264               |1242           |11             |
> 
> With a similar number of NAT blocks accessed and read from disk, adding
> NAT block readahead reduces the total NAT block flush time by more than
> 90%.
> 
> Signed-off-by: Yongpeng Yang <yangyongpeng@xiaomi.com>

Reviewed-by: Chao Yu <chao@kernel.org>

Thanks,


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