The patch titled Subject: mm/mglru: respect min_ttl_ms with memcgs has been added to the -mm mm-hotfixes-unstable branch. Its filename is mm-mglru-respect-min_ttl_ms-with-memcgs.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-mglru-respect-min_ttl_ms-with-memcgs.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: respect min_ttl_ms with memcgs Date: Thu, 7 Dec 2023 23:14:06 -0700 While investigating kswapd "consuming 100% CPU" [1] (also see "mm/mglru: try to stop at high watermarks"), it was discovered that the memcg LRU can breach the thrashing protection imposed by min_ttl_ms. Before the memcg LRU: kswapd() shrink_node_memcgs() mem_cgroup_iter() inc_max_seq() // always hit a different memcg lru_gen_age_node() mem_cgroup_iter() check the timestamp of the oldest generation After the memcg LRU: kswapd() shrink_many() restart: iterate the memcg LRU: inc_max_seq() // occasionally hit the same memcg if raced with lru_gen_rotate_memcg(): goto restart lru_gen_age_node() mem_cgroup_iter() check the timestamp of the oldest generation Specifically, when the restart happens in shrink_many(), it needs to stick with the (memcg LRU) generation it began with. In other words, it should neither re-read memcg_lru->seq nor age an lruvec of a different generation. Otherwise it can hit the same memcg multiple times without giving lru_gen_age_node() a chance to check the timestamp of that memcg's oldest generation (against min_ttl_ms). [1] https://lore.kernel.org/CAK8fFZ4DY+GtBA40Pm7Nn5xCHy+51w3sfxPqkqpqakSXYyX+Wg@xxxxxxxxxxxxxx/ Link: https://lkml.kernel.org/r/20231208061407.2125867-3-yuzhao@xxxxxxxxxx Fixes: e4dde56cd208 ("mm: multi-gen LRU: per-node lru_gen_folio lists") Signed-off-by: Yu Zhao <yuzhao@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 | 30 +++++++++++++++++------------- mm/vmscan.c | 30 ++++++++++++++++-------------- 2 files changed, 33 insertions(+), 27 deletions(-) --- a/include/linux/mmzone.h~mm-mglru-respect-min_ttl_ms-with-memcgs +++ a/include/linux/mmzone.h @@ -505,33 +505,37 @@ void lru_gen_look_around(struct page_vma * the old generation, is incremented when all its bins become empty. * * There are four operations: - * 1. MEMCG_LRU_HEAD, which moves an memcg to the head of a random bin in its + * 1. MEMCG_LRU_HEAD, which moves a memcg to the head of a random bin in its * current generation (old or young) and updates its "seg" to "head"; - * 2. MEMCG_LRU_TAIL, which moves an memcg to the tail of a random bin in its + * 2. MEMCG_LRU_TAIL, which moves a memcg to the tail of a random bin in its * current generation (old or young) and updates its "seg" to "tail"; - * 3. MEMCG_LRU_OLD, which moves an memcg to the head of a random bin in the old + * 3. MEMCG_LRU_OLD, which moves a memcg to the head of a random bin in the old * generation, updates its "gen" to "old" and resets its "seg" to "default"; - * 4. MEMCG_LRU_YOUNG, which moves an memcg to the tail of a random bin in the + * 4. MEMCG_LRU_YOUNG, which moves a memcg to the tail of a random bin in the * young generation, updates its "gen" to "young" and resets its "seg" to * "default". * * The events that trigger the above operations are: * 1. Exceeding the soft limit, which triggers MEMCG_LRU_HEAD; - * 2. The first attempt to reclaim an memcg below low, which triggers + * 2. The first attempt to reclaim a memcg below low, which triggers * MEMCG_LRU_TAIL; - * 3. The first attempt to reclaim an memcg below reclaimable size threshold, + * 3. The first attempt to reclaim a memcg below reclaimable size threshold, * which triggers MEMCG_LRU_TAIL; - * 4. The second attempt to reclaim an memcg below reclaimable size threshold, + * 4. The second attempt to reclaim a memcg below reclaimable size threshold, * which triggers MEMCG_LRU_YOUNG; - * 5. Attempting to reclaim an memcg below min, 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 an memcg, which triggers MEMCG_LRU_OLD. + * 7. Offlining a memcg, which triggers MEMCG_LRU_OLD. * - * Note that memcg LRU only applies to global reclaim, and the round-robin - * incrementing of their max_seq counters ensures the eventual fairness to all - * eligible memcgs. For memcg reclaim, it still relies on mem_cgroup_iter(). + * Notes: + * 1. Memcg LRU only applies to global reclaim, and the round-robin incrementing + * of their max_seq counters ensures the eventual fairness to all eligible + * memcgs. For memcg reclaim, it still relies on mem_cgroup_iter(). + * 2. There are only two valid generations: old (seq) and young (seq+1). + * MEMCG_NR_GENS is set to three so that when reading the generation counter + * locklessly, a stale value (seq-1) does not wraparound to young. */ -#define MEMCG_NR_GENS 2 +#define MEMCG_NR_GENS 3 #define MEMCG_NR_BINS 8 struct lru_gen_memcg { --- a/mm/vmscan.c~mm-mglru-respect-min_ttl_ms-with-memcgs +++ a/mm/vmscan.c @@ -4089,6 +4089,9 @@ static void lru_gen_rotate_memcg(struct else VM_WARN_ON_ONCE(true); + WRITE_ONCE(lruvec->lrugen.seg, seg); + WRITE_ONCE(lruvec->lrugen.gen, new); + hlist_nulls_del_rcu(&lruvec->lrugen.list); if (op == MEMCG_LRU_HEAD || op == MEMCG_LRU_OLD) @@ -4099,9 +4102,6 @@ static void lru_gen_rotate_memcg(struct pgdat->memcg_lru.nr_memcgs[old]--; pgdat->memcg_lru.nr_memcgs[new]++; - lruvec->lrugen.gen = new; - WRITE_ONCE(lruvec->lrugen.seg, seg); - if (!pgdat->memcg_lru.nr_memcgs[old] && old == get_memcg_gen(pgdat->memcg_lru.seq)) WRITE_ONCE(pgdat->memcg_lru.seq, pgdat->memcg_lru.seq + 1); @@ -4124,11 +4124,11 @@ void lru_gen_online_memcg(struct mem_cgr gen = get_memcg_gen(pgdat->memcg_lru.seq); + lruvec->lrugen.gen = gen; + hlist_nulls_add_tail_rcu(&lruvec->lrugen.list, &pgdat->memcg_lru.fifo[gen][bin]); pgdat->memcg_lru.nr_memcgs[gen]++; - lruvec->lrugen.gen = gen; - spin_unlock_irq(&pgdat->memcg_lru.lock); } } @@ -4635,7 +4635,7 @@ static long get_nr_to_scan(struct lruvec DEFINE_MAX_SEQ(lruvec); if (mem_cgroup_below_min(sc->target_mem_cgroup, memcg)) - return 0; + return -1; if (!should_run_aging(lruvec, max_seq, sc, can_swap, &nr_to_scan)) return nr_to_scan; @@ -4710,7 +4710,7 @@ static bool try_to_shrink_lruvec(struct cond_resched(); } - /* whether try_to_inc_max_seq() was successful */ + /* whether this lruvec should be rotated */ return nr_to_scan < 0; } @@ -4764,13 +4764,13 @@ static void shrink_many(struct pglist_da struct lruvec *lruvec; struct lru_gen_folio *lrugen; struct mem_cgroup *memcg; - const struct hlist_nulls_node *pos; + struct hlist_nulls_node *pos; + gen = get_memcg_gen(READ_ONCE(pgdat->memcg_lru.seq)); bin = first_bin = get_random_u32_below(MEMCG_NR_BINS); restart: op = 0; memcg = NULL; - gen = get_memcg_gen(READ_ONCE(pgdat->memcg_lru.seq)); rcu_read_lock(); @@ -4781,6 +4781,10 @@ restart: } mem_cgroup_put(memcg); + memcg = NULL; + + if (gen != READ_ONCE(lrugen->gen)) + continue; lruvec = container_of(lrugen, struct lruvec, lrugen); memcg = lruvec_memcg(lruvec); @@ -4865,16 +4869,14 @@ static void set_initial_priority(struct if (sc->priority != DEF_PRIORITY || sc->nr_to_reclaim < MIN_LRU_BATCH) return; /* - * Determine the initial priority based on ((total / MEMCG_NR_GENS) >> - * priority) * reclaimed_to_scanned_ratio = nr_to_reclaim, where the - * estimated reclaimed_to_scanned_ratio = inactive / total. + * Determine the initial priority based on + * (total >> priority) * reclaimed_to_scanned_ratio = nr_to_reclaim, + * where reclaimed_to_scanned_ratio = inactive / total. */ reclaimable = node_page_state(pgdat, NR_INACTIVE_FILE); if (get_swappiness(lruvec, sc)) reclaimable += node_page_state(pgdat, NR_INACTIVE_ANON); - reclaimable /= MEMCG_NR_GENS; - /* round down reclaimable and round up sc->nr_to_reclaim */ priority = fls_long(reclaimable) - 1 - fls_long(sc->nr_to_reclaim - 1); _ 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