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This leads to premature OOM if there are too many dirty pages in cgroup: Killed dd invoked oom-killer: gfp_mask=3D0x101cca(GFP_HIGHUSER_MOVABLE|__GFP_WRITE= ), order=3D0, oom_score_adj=3D0 Call Trace: dump_stack_lvl+0x5f/0x80 dump_stack+0x14/0x20 dump_header+0x46/0x1b0 oom_kill_process+0x104/0x220 out_of_memory+0x112/0x5a0 mem_cgroup_out_of_memory+0x13b/0x150 try_charge_memcg+0x44f/0x5c0 charge_memcg+0x34/0x50 __mem_cgroup_charge+0x31/0x90 filemap_add_folio+0x4b/0xf0 __filemap_get_folio+0x1a4/0x5b0 ? srso_return_thunk+0x5/0x5f ? __block_commit_write+0x82/0xb0 ext4_da_write_begin+0xe5/0x270 generic_perform_write+0x134/0x2b0 ext4_buffered_write_iter+0x57/0xd0 ext4_file_write_iter+0x76/0x7d0 ? selinux_file_permission+0x119/0x150 ? srso_return_thunk+0x5/0x5f ? srso_return_thunk+0x5/0x5f vfs_write+0x30c/0x440 ksys_write+0x65/0xe0 __x64_sys_write+0x1e/0x30 x64_sys_call+0x11c2/0x1d50 do_syscall_64+0x47/0x110 entry_SYSCALL_64_after_hwframe+0x76/0x7e memory: usage 308224kB, limit 308224kB, failcnt 2589 swap: usage 0kB, limit 9007199254740988kB, failcnt 0 ... file_dirty 303247360 file_writeback 0 ... oom-kill:constraint=3DCONSTRAINT_MEMCG,nodemask=3D(null),cpuset=3Dtest, mems_allowed=3D0,oom_memcg=3D/test,task_memcg=3D/test,task=3Ddd,pid=3D4404,= uid=3D0 Memory cgroup out of memory: Killed process 4404 (dd) total-vm:10512kB, anon-rss:1152kB, file-rss:1824kB, shmem-rss:0kB, UID:0 pgtables:76kB oom_score_adj:0 The flusher wake up was removed to decrease SSD wearing, but if we are seeing all dirty folios at the tail of an LRU, not waking up the flusher could lead to thrashing easily. So wake it up when a mem cgroups is about to OOM due to dirty caches. I did run the build kernel test[1] on V5, with -j16 1G memcg on my local branch: Without the patch(10 times): user 1473.29 system 347.87 339.17 345.28 354.64 352.46 355.63 358.80 359.40 358.28 350.95 (avg 352.248) real 166.651 With the V5 patch(10 times): user 1470.7 system 339.13 350.58 350.07 355.58 348.96 344.83 351.78 336.39 350.45 343.31 (avg 347.108) real 165.821 Test results show that this patch has about 1% performance improvement, which should be caused by noise. --- Changes from v4: - Add the number of unqueued dirty pages in the shrink_folio_list function to sc->nr.unqueued_dirty. [Wei Xu, Jingxiang Zeng] - Reset sc->nr before calling lru_gen_shrink_node function. [Wei Xu, Jingxiang Zeng] - Modified the conditions for waking up the flusher thread to avoid interference from unevictable and anonymous pages. [Wei Xu, Jingxiang Zeng] - Link to v4: https://lore.kernel.org/all/20240929113050.76079-1-jingxiangz= eng.cas@gmail.com/ Changes from v3: - Avoid taking lock and reduce overhead on folio isolation by checking the right flags and rework wake up condition, fixing the performance regression reported by Chris Li. [Chris Li, Kairui Song] - Move the wake up check to try_to_shrink_lruvec to cover kswapd case as well, and update comments. [Kairui Song] - Link to v3: https://lore.kernel.org/all/20240924121358.30685-1-jingxiangz= eng.cas@gmail.com/ Changes from v2: - Acquire the lock before calling the folio_check_dirty_writeback function. [Wei Xu, Jingxiang Zeng] - Link to v2: https://lore.kernel.org/all/20240913084506.3606292-1-jingxian= gzeng.cas@gmail.com/ Changes from v1: - Add code to count the number of unqueued_dirty in the sort_folio function. [Wei Xu, Jingxiang Zeng] - Link to v1: https://lore.kernel.org/all/20240829102543.189453-1-jingxiang= zeng.cas@gmail.com/ --- Link: https://lore.kernel.org/all/CACePvbV4L-gRN9UKKuUnksfVJjOTq_5Sti2-e=3D= pb_w51kucLKQ@mail.gmail.com/ [1] Fixes: 14aa8b2d5c2e ("mm/mglru: don't sync disk for each aging cycle") Signed-off-by: Zeng Jingxiang Signed-off-by: Kairui Song Cc: T.J. Mercier Cc: Wei Xu Cc: Yu Zhao --- mm/vmscan.c | 22 +++++++++++++++++++--- 1 file changed, 19 insertions(+), 3 deletions(-) diff --git a/mm/vmscan.c b/mm/vmscan.c index 2d0486189804..97e0af338ee0 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -4292,6 +4292,7 @@ static bool sort_folio(struct lruvec *lruvec, struct = folio *folio, struct scan_c int tier_idx) { bool success; + bool dirty, writeback; int gen =3D folio_lru_gen(folio); int type =3D folio_is_file_lru(folio); int zone =3D folio_zonenum(folio); @@ -4337,9 +4338,14 @@ static bool sort_folio(struct lruvec *lruvec, struct= folio *folio, struct scan_c return true; } =20 + dirty =3D folio_test_dirty(folio); + writeback =3D folio_test_writeback(folio); + if (type =3D=3D LRU_GEN_FILE && dirty && !writeback) + sc->nr.unqueued_dirty +=3D delta; + /* waiting for writeback */ - if (folio_test_locked(folio) || folio_test_writeback(folio) || - (type =3D=3D LRU_GEN_FILE && folio_test_dirty(folio))) { + if (folio_test_locked(folio) || writeback || + (type =3D=3D LRU_GEN_FILE && dirty)) { gen =3D folio_inc_gen(lruvec, folio, true); list_move(&folio->lru, &lrugen->folios[gen][type][zone]); return true; @@ -4455,7 +4461,8 @@ static int scan_folios(struct lruvec *lruvec, struct = scan_control *sc, trace_mm_vmscan_lru_isolate(sc->reclaim_idx, sc->order, MAX_LRU_BATCH, scanned, skipped, isolated, type ? LRU_INACTIVE_FILE : LRU_INACTIVE_ANON); - + if (type =3D=3D LRU_GEN_FILE) + sc->nr.taken +=3D isolated; /* * There might not be eligible folios due to reclaim_idx. Check the * remaining to prevent livelock if it's not making progress. @@ -4589,6 +4596,7 @@ static int evict_folios(struct lruvec *lruvec, struct= scan_control *sc, int swap return scanned; retry: reclaimed =3D shrink_folio_list(&list, pgdat, sc, &stat, false); + sc->nr.unqueued_dirty +=3D stat.nr_unqueued_dirty; sc->nr_reclaimed +=3D reclaimed; trace_mm_vmscan_lru_shrink_inactive(pgdat->node_id, scanned, reclaimed, &stat, sc->priority, @@ -4797,6 +4805,13 @@ static bool try_to_shrink_lruvec(struct lruvec *lruv= ec, struct scan_control *sc) cond_resched(); } =20 + /* + * If too many file cache in the coldest generation can't be evicted + * due to being dirty, wake up the flusher. + */ + if (sc->nr.unqueued_dirty && !sc->nr.taken) + wakeup_flusher_threads(WB_REASON_VMSCAN); + /* whether this lruvec should be rotated */ return nr_to_scan < 0; } @@ -5942,6 +5957,7 @@ static void shrink_node(pg_data_t *pgdat, struct scan= _control *sc) bool reclaimable =3D false; =20 if (lru_gen_enabled() && root_reclaim(sc)) { + memset(&sc->nr, 0, sizeof(sc->nr)); lru_gen_shrink_node(pgdat, sc); return; } --=20 2.43.5