On 1/13/2026 11:23 PM, Yongpeng Yang wrote:
From: Yongpeng Yang <[email protected]>
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 <[email protected]>
Reviewed-by: Chao Yu <[email protected]>
Thanks,
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