nat_cnt[] is updated while callers hold nat_tree_lock, but F2FS samples the counters locklessly in f2fs_available_free_memory(), excess_dirty_nats(), and excess_cached_nats(). Those helpers only steer cache reclaim and background sync heuristics; they do not control NAT entry lifetime or checkpoint correctness.
Document the intent with data_race(READ_ONCE()) and a short comment instead of adding locking to the balance path. Signed-off-by: Cen Zhang <[email protected]> --- fs/f2fs/node.c | 6 +++++- fs/f2fs/node.h | 8 ++++++-- 2 files changed, 11 insertions(+), 3 deletions(-) diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c index 74992fd9c9b6..8318c747600d 100644 --- a/fs/f2fs/node.c +++ b/fs/f2fs/node.c @@ -72,7 +72,11 @@ bool f2fs_available_free_memory(struct f2fs_sb_info *sbi, int type) sizeof(struct free_nid)) >> PAGE_SHIFT; res = mem_size < ((avail_ram * nm_i->ram_thresh / 100) >> 2); } else if (type == NAT_ENTRIES) { - mem_size = (nm_i->nat_cnt[TOTAL_NAT] * + /* + * nat_cnt[] is heuristic accounting. Sample it locklessly here + * to avoid taking nat_tree_lock in the balance path. + */ + mem_size = (data_race(READ_ONCE(nm_i->nat_cnt[TOTAL_NAT])) * sizeof(struct nat_entry)) >> PAGE_SHIFT; res = mem_size < ((avail_ram * nm_i->ram_thresh / 100) >> 2); if (excess_cached_nats(sbi)) diff --git a/fs/f2fs/node.h b/fs/f2fs/node.h index 824ac9f0e6e4..c1aa41b31d66 100644 --- a/fs/f2fs/node.h +++ b/fs/f2fs/node.h @@ -129,13 +129,17 @@ static inline void raw_nat_from_node_info(struct f2fs_nat_entry *raw_ne, static inline bool excess_dirty_nats(struct f2fs_sb_info *sbi) { - return NM_I(sbi)->nat_cnt[DIRTY_NAT] >= NM_I(sbi)->max_nid * + /* nat_cnt[] is heuristic accounting sampled locklessly here. */ + return data_race(READ_ONCE(NM_I(sbi)->nat_cnt[DIRTY_NAT])) >= + NM_I(sbi)->max_nid * NM_I(sbi)->dirty_nats_ratio / 100; } static inline bool excess_cached_nats(struct f2fs_sb_info *sbi) { - return NM_I(sbi)->nat_cnt[TOTAL_NAT] >= DEF_NAT_CACHE_THRESHOLD; + /* nat_cnt[] is heuristic accounting sampled locklessly here. */ + return data_race(READ_ONCE(NM_I(sbi)->nat_cnt[TOTAL_NAT])) >= + DEF_NAT_CACHE_THRESHOLD; } enum mem_type { -- 2.43.0 _______________________________________________ Linux-f2fs-devel mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
