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I should've applied v5's change in v4. > > > > Changes from v4: > > 1. Make other scans start with may_cache_trim_mode = 1. > > > > Changes from v3: > > 1. Update the test result in the commit message with v4. > > 2. Retry the whole priority loop with cache_trim_mode off again, > > rather than forcing the mode off at the highest priority, > > when the mode doesn't work. (feedbacked by Johannes Weiner) > > > > Changes from v2: > > 1. Change the condition to stop cache_trim_mode. > > > > From - Stop it if it's at high scan priorities, 0 or 1. > > To - Stop it if it's at high scan priorities, 0 or 1, and > > the mode didn't work in the previous turn. > > > > (feedbacked by Huang Ying) > > > > 2. Change the test result in the commit message after testing > > with the new logic. > > > > Changes from v1: > > 1. Add a comment describing why this change is necessary in code > > and rewrite the commit message with how to reproduce and what > > the result is using vmstat. (feedbacked by Andrew Morton and > > Yu Zhao) > > 2. Change the condition to avoid cache_trim_mode from > > 'sc->priority != 1' to 'sc->priority > 1' to reflect cases > > where the priority goes to zero all the way. (feedbacked by > > Yu Zhao) > > --->8--- > > From 58f1a0e41b9feea72d7fd4bd7bed1ace592e6e4c Mon Sep 17 00:00:00 2001 > > From: Byungchul Park > > Date: Mon, 4 Mar 2024 11:24:40 +0900 > > Subject: [PATCH v5] mm, vmscan: retry kswapd's priority loop with cache_trim_mode off on failure > > > > With cache_trim_mode on, reclaim logic doesn't bother reclaiming anon > > pages. However, it should be more careful to use the mode because it's > > going to prevent anon pages from being reclaimed even if there are a > > huge number of anon pages that are cold and should be reclaimed. Even > > worse, that leads kswapd_failures to reach MAX_RECLAIM_RETRIES and > > stopping kswapd from functioning until direct reclaim eventually works > > to resume kswapd. > > > > So kswapd needs to retry its scan priority loop with cache_trim_mode > > off again if the mode doesn't work for reclaim. > > > > The problematic behavior can be reproduced by: > > > > CONFIG_NUMA_BALANCING enabled > > sysctl_numa_balancing_mode set to NUMA_BALANCING_MEMORY_TIERING > > numa node0 (8GB local memory, 16 CPUs) > > numa node1 (8GB slow tier memory, no CPUs) > > > > Sequence: > > > > 1) echo 3 > /proc/sys/vm/drop_caches > > 2) To emulate the system with full of cold memory in local DRAM, run > > the following dummy program and never touch the region: > > > > mmap(0, 8 * 1024 * 1024 * 1024, PROT_READ | PROT_WRITE, > > MAP_ANONYMOUS | MAP_PRIVATE | MAP_POPULATE, -1, 0); > > > > 3) Run any memory intensive work e.g. XSBench. > > 4) Check if numa balancing is working e.i. promotion/demotion. > > 5) Iterate 1) ~ 4) until numa balancing stops. > > > > With this, you could see that promotion/demotion are not working because > > kswapd has stopped due to ->kswapd_failures >= MAX_RECLAIM_RETRIES. > > > > Interesting vmstat delta's differences between before and after are like: > > > > +-----------------------+-------------------------------+ > > | interesting vmstat | before | after | > > +-----------------------+-------------------------------+ > > | nr_inactive_anon | 321935 | 1646193 | > > | nr_active_anon | 1780700 | 456388 | > > | nr_inactive_file | 30425 | 27836 | > > | nr_active_file | 14961 | 1217 | > > | pgpromote_success | 356 | 1310120 | > > | pgpromote_candidate | 21953245 | 1736872 | > > | pgactivate | 1844523 | 3292443 | > > | pgdeactivate | 50634 | 1526701 | > > | pgfault | 31100294 | 6715375 | > > | pgdemote_kswapd | 30856 | 1954199 | > > | pgscan_kswapd | 1861981 | 7100099 | > > | pgscan_anon | 1822930 | 7061135 | > > | pgscan_file | 39051 | 38964 | > > | pgsteal_anon | 386 | 1925214 | > > | pgsteal_file | 30470 | 28985 | > > | pageoutrun | 30 | 500 | > > | numa_hint_faults | 27418279 | 3090773 | > > | numa_pages_migrated | 356 | 1310120 | > > +-----------------------+-------------------------------+ > > > > Signed-off-by: Byungchul Park > > --- > > mm/vmscan.c | 23 +++++++++++++++++++++-- > > 1 file changed, 21 insertions(+), 2 deletions(-) > > > > diff --git a/mm/vmscan.c b/mm/vmscan.c > > index bba207f41b14..77948b0f8b5b 100644 > > --- a/mm/vmscan.c > > +++ b/mm/vmscan.c > > @@ -108,6 +108,9 @@ struct scan_control { > > /* Can folios be swapped as part of reclaim? */ > > unsigned int may_swap:1; > > > > + /* Can cache_trim_mode be turned on as part of reclaim? */ > > + unsigned int may_cache_trim_mode:1; > > + > > Although it's generally not good to use negative logic, I think that > it's better to name the flag as something like "no_cache_trim_mode" to > make it easier to initialize the flag to its default value ("0"). No preference to me. But don't think it's better to use another of may_* in scan_control as Johannes Weiner suggested? > > /* Proactive reclaim invoked by userspace through memory.reclaim */ > > unsigned int proactive:1; > > > > @@ -1500,6 +1503,7 @@ unsigned int reclaim_clean_pages_from_list(struct zone *zone, > > struct scan_control sc = { > > .gfp_mask = GFP_KERNEL, > > .may_unmap = 1, > > + .may_cache_trim_mode = 1, > > }; > > struct reclaim_stat stat; > > unsigned int nr_reclaimed; > > @@ -2094,6 +2098,7 @@ static unsigned int reclaim_folio_list(struct list_head *folio_list, > > .may_writepage = 1, > > .may_unmap = 1, > > .may_swap = 1, > > + .may_cache_trim_mode = 1, > > .no_demotion = 1, > > }; > > > > @@ -2268,7 +2273,8 @@ static void prepare_scan_control(pg_data_t *pgdat, struct scan_control *sc) > > * anonymous pages. > > */ > > file = lruvec_page_state(target_lruvec, NR_INACTIVE_FILE); > > - if (file >> sc->priority && !(sc->may_deactivate & DEACTIVATE_FILE)) > > + if (file >> sc->priority && !(sc->may_deactivate & DEACTIVATE_FILE) && > > + sc->may_cache_trim_mode) > > sc->cache_trim_mode = 1; > > else > > sc->cache_trim_mode = 0; > > @@ -5435,6 +5441,7 @@ static ssize_t lru_gen_seq_write(struct file *file, const char __user *src, > > .may_writepage = true, > > .may_unmap = true, > > .may_swap = true, > > + .may_cache_trim_mode = 1, > > .reclaim_idx = MAX_NR_ZONES - 1, > > .gfp_mask = GFP_KERNEL, > > }; > > @@ -6394,6 +6401,7 @@ unsigned long try_to_free_pages(struct zonelist *zonelist, int order, > > .may_writepage = !laptop_mode, > > .may_unmap = 1, > > .may_swap = 1, > > + .may_cache_trim_mode = 1, > > }; > > > > /* > > @@ -6439,6 +6447,7 @@ unsigned long mem_cgroup_shrink_node(struct mem_cgroup *memcg, > > .may_unmap = 1, > > .reclaim_idx = MAX_NR_ZONES - 1, > > .may_swap = !noswap, > > + .may_cache_trim_mode = 1, > > }; > > > > WARN_ON_ONCE(!current->reclaim_state); > > @@ -6482,6 +6491,7 @@ unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg, > > .may_writepage = !laptop_mode, > > .may_unmap = 1, > > .may_swap = !!(reclaim_options & MEMCG_RECLAIM_MAY_SWAP), > > + .may_cache_trim_mode = 1, > > .proactive = !!(reclaim_options & MEMCG_RECLAIM_PROACTIVE), > > }; > > /* > > @@ -6744,6 +6754,7 @@ static int balance_pgdat(pg_data_t *pgdat, int order, int highest_zoneidx) > > .gfp_mask = GFP_KERNEL, > > .order = order, > > .may_unmap = 1, > > + .may_cache_trim_mode = 1, > > }; > > > > set_task_reclaim_state(current, &sc.reclaim_state); > > @@ -6898,8 +6909,14 @@ static int balance_pgdat(pg_data_t *pgdat, int order, int highest_zoneidx) > > sc.priority--; > > } while (sc.priority >= 1); > > > > - if (!sc.nr_reclaimed) > > + if (!sc.nr_reclaimed) { > > + if (sc.may_cache_trim_mode) { > > sc.may_cache_trim_mode && cache_trim_mode ? I don't think so. cache_trim_mode has a chance to switch every prepare_scan_control() like: if (file >> sc->priority && !(sc->may_deactivate & DEACTIVATE_FILE) && sc->may_cache_trim_mode) sc->cache_trim_mode = 1; else sc->cache_trim_mode = 0; So referring to the last value is not a good idea. Byungchul > > + sc.may_cache_trim_mode = 0; > > + goto restart; > > + } > > + > > pgdat->kswapd_failures++; > > + } > > > > out: > > clear_reclaim_active(pgdat, highest_zoneidx); > > @@ -7202,6 +7219,7 @@ unsigned long shrink_all_memory(unsigned long nr_to_reclaim) > > .may_writepage = 1, > > .may_unmap = 1, > > .may_swap = 1, > > + .may_cache_trim_mode = 1, > > .hibernation_mode = 1, > > }; > > struct zonelist *zonelist = node_zonelist(numa_node_id(), sc.gfp_mask); > > @@ -7360,6 +7378,7 @@ static int __node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned in > > .may_writepage = !!(node_reclaim_mode & RECLAIM_WRITE), > > .may_unmap = !!(node_reclaim_mode & RECLAIM_UNMAP), > > .may_swap = 1, > > + .may_cache_trim_mode = 1, > > .reclaim_idx = gfp_zone(gfp_mask), > > }; > > unsigned long pflags; > > -- > Best Regards, > Huang, Ying