The patch titled Subject: mm/mglru: reclaim offlined memcgs harder has been added to the -mm mm-hotfixes-unstable branch. Its filename is mm-mglru-reclaim-offlined-memcgs-harder.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-mglru-reclaim-offlined-memcgs-harder.patch This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next via the mm-everything branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there every 2-3 working days ------------------------------------------------------ From: Yu Zhao <yuzhao@xxxxxxxxxx> Subject: mm/mglru: reclaim offlined memcgs harder Date: Thu, 7 Dec 2023 23:14:07 -0700 In the effort to reduce zombie memcgs [1], it was discovered that the memcg LRU doesn't apply enough pressure on offlined memcgs. Specifically, instead of rotating them to the tail of the current generation (MEMCG_LRU_TAIL) for a second attempt, it moves them to the next generation (MEMCG_LRU_YOUNG) after the first attempt. Not applying enough pressure on offlined memcgs can cause them to build up, and this can be particularly harmful to memory-constrained systems. On Pixel 8 Pro, launching apps for 50 cycles: Before After Change Zombie memcgs 45 35 -22% [1] https://lore.kernel.org/CABdmKX2M6koq4Q0Cmp_-=wbP0Qa190HdEGGaHfxNS05gAkUtPA@xxxxxxxxxxxxxx/ Link: https://lkml.kernel.org/r/20231208061407.2125867-4-yuzhao@xxxxxxxxxx Fixes: e4dde56cd208 ("mm: multi-gen LRU: per-node lru_gen_folio lists") Signed-off-by: Yu Zhao <yuzhao@xxxxxxxxxx> Reported-by: T.J. Mercier <tjmercier@xxxxxxxxxx> Tested-by: T.J. Mercier <tjmercier@xxxxxxxxxx> Cc: Charan Teja Kalla <quic_charante@xxxxxxxxxxx> Cc: Hillf Danton <hdanton@xxxxxxxx> Cc: Jaroslav Pulchart <jaroslav.pulchart@xxxxxxxxxxxx> Cc: Kairui Song <ryncsn@xxxxxxxxx> Cc: Kalesh Singh <kaleshsingh@xxxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- include/linux/mmzone.h | 8 ++++---- mm/vmscan.c | 24 ++++++++++++++++-------- 2 files changed, 20 insertions(+), 12 deletions(-) --- a/include/linux/mmzone.h~mm-mglru-reclaim-offlined-memcgs-harder +++ a/include/linux/mmzone.h @@ -519,10 +519,10 @@ void lru_gen_look_around(struct page_vma * 1. Exceeding the soft limit, which triggers MEMCG_LRU_HEAD; * 2. The first attempt to reclaim a memcg below low, which triggers * MEMCG_LRU_TAIL; - * 3. The first attempt to reclaim a memcg below reclaimable size threshold, - * which triggers MEMCG_LRU_TAIL; - * 4. The second attempt to reclaim a memcg below reclaimable size threshold, - * which triggers MEMCG_LRU_YOUNG; + * 3. The first attempt to reclaim a memcg offlined or below reclaimable size + * threshold, which triggers MEMCG_LRU_TAIL; + * 4. The second attempt to reclaim a memcg offlined or below reclaimable size + * threshold, which triggers MEMCG_LRU_YOUNG; * 5. Attempting to reclaim a memcg below min, which triggers MEMCG_LRU_YOUNG; * 6. Finishing the aging on the eviction path, which triggers MEMCG_LRU_YOUNG; * 7. Offlining a memcg, which triggers MEMCG_LRU_OLD. --- a/mm/vmscan.c~mm-mglru-reclaim-offlined-memcgs-harder +++ a/mm/vmscan.c @@ -4598,7 +4598,12 @@ static bool should_run_aging(struct lruv } /* try to scrape all its memory if this memcg was deleted */ - *nr_to_scan = mem_cgroup_online(memcg) ? (total >> sc->priority) : total; + if (!mem_cgroup_online(memcg)) { + *nr_to_scan = total; + return false; + } + + *nr_to_scan = total >> sc->priority; /* * The aging tries to be lazy to reduce the overhead, while the eviction @@ -4719,14 +4724,9 @@ static int shrink_one(struct lruvec *lru bool success; unsigned long scanned = sc->nr_scanned; unsigned long reclaimed = sc->nr_reclaimed; - int seg = lru_gen_memcg_seg(lruvec); struct mem_cgroup *memcg = lruvec_memcg(lruvec); struct pglist_data *pgdat = lruvec_pgdat(lruvec); - /* see the comment on MEMCG_NR_GENS */ - if (!lruvec_is_sizable(lruvec, sc)) - return seg != MEMCG_LRU_TAIL ? MEMCG_LRU_TAIL : MEMCG_LRU_YOUNG; - mem_cgroup_calculate_protection(NULL, memcg); if (mem_cgroup_below_min(NULL, memcg)) @@ -4734,7 +4734,7 @@ static int shrink_one(struct lruvec *lru if (mem_cgroup_below_low(NULL, memcg)) { /* see the comment on MEMCG_NR_GENS */ - if (seg != MEMCG_LRU_TAIL) + if (lru_gen_memcg_seg(lruvec) != MEMCG_LRU_TAIL) return MEMCG_LRU_TAIL; memcg_memory_event(memcg, MEMCG_LOW); @@ -4750,7 +4750,15 @@ static int shrink_one(struct lruvec *lru flush_reclaim_state(sc); - return success ? MEMCG_LRU_YOUNG : 0; + if (success && mem_cgroup_online(memcg)) + return MEMCG_LRU_YOUNG; + + if (!success && lruvec_is_sizable(lruvec, sc)) + return 0; + + /* one retry if offlined or too small */ + return lru_gen_memcg_seg(lruvec) != MEMCG_LRU_TAIL ? + MEMCG_LRU_TAIL : MEMCG_LRU_YOUNG; } #ifdef CONFIG_MEMCG _ Patches currently in -mm which might be from yuzhao@xxxxxxxxxx are mm-mglru-fix-underprotected-page-cache.patch mm-mglru-try-to-stop-at-high-watermarks.patch mm-mglru-respect-min_ttl_ms-with-memcgs.patch mm-mglru-reclaim-offlined-memcgs-harder.patch