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f2fs: optimize NAT block loading during checkpoint write

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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>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
This commit is contained in:
Yongpeng Yang
2026-01-13 23:23:15 +08:00
committed by Jaegeuk Kim
parent 7c9ee0ed2b
commit 1db4b3609a
1 changed files with 13 additions and 1 deletions
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14
fs/f2fs/node.c
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@@ -3179,7 +3179,7 @@ int f2fs_flush_nat_entries(struct f2fs_sb_info *sbi, struct cp_control *cpc)
struct f2fs_journal *journal = curseg->journal;
struct nat_entry_set *setvec[NAT_VEC_SIZE];
struct nat_entry_set *set, *tmp;
unsigned int found;
unsigned int found, entry_count = 0;
nid_t set_idx = 0;
LIST_HEAD(sets);
int err = 0;
@@ -3219,6 +3219,18 @@ int f2fs_flush_nat_entries(struct f2fs_sb_info *sbi, struct cp_control *cpc)
MAX_NAT_JENTRIES(sbi, journal));
}
/*
* Readahead the current NAT block to prevent read requests from
* being issued and waited on one by one.
*/
list_for_each_entry(set, &sets, set_list) {
entry_count += set->entry_cnt;
if (!enabled_nat_bits(sbi, cpc) &&
__has_cursum_space(sbi, journal,
entry_count, NAT_JOURNAL))
continue;
f2fs_ra_meta_pages(sbi, set->set, 1, META_NAT, true);
}
/* flush dirty nats in nat entry set */
list_for_each_entry_safe(set, tmp, &sets, set_list) {
err = __flush_nat_entry_set(sbi, set, cpc);