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s=arc-20220608; d=hostedemail.com; t=1709523382; a=rsa-sha256; cv=none; b=h9q8+K4BF3Ohi62OYaGkdWrk7fE4Rp48cxBsShBY7yYM3tlj62e+UkWAKAMLeUHJU4WT54 ZG9OAgFRArakaMVzK09zY6pFmBmf1vEyiKec6fIFNExZsDJrXCVmH3b1ZWjuGVwDvdujFi BM++efZvyzlY7XEmYJgwaf4xdhjjBH4= ARC-Authentication-Results: i=1; imf10.hostedemail.com; dkim=none; spf=pass (imf10.hostedemail.com: domain of byungchul@sk.com designates 166.125.252.92 as permitted sender) smtp.mailfrom=byungchul@sk.com; dmarc=none X-AuditID: a67dfc5b-d6dff70000001748-e5-65e541b0c539 Date: Mon, 4 Mar 2024 12:36:11 +0900 From: Byungchul Park To: "Huang, Ying" Cc: akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, kernel_team@skhynix.com, yuzhao@google.com, hannes@cmpxchg.org Subject: Re: [PATCH v5] mm, vmscan: retry kswapd's priority loop with cache_trim_mode off on failure Message-ID: <20240304033611.GD13332@system.software.com> References: <20240304023018.69705-1-byungchul@sk.com> <87bk7ubtd4.fsf@yhuang6-desk2.ccr.corp.intel.com> <20240304030413.GC13332@system.software.com> <877ciibrp9.fsf@yhuang6-desk2.ccr.corp.intel.com> MIME-Version: 1.0 Content-Type: text/plain; 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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. > > We should only restart without cache_trim_mode if cache_trim_mode causes > issue. If it isn't enabled with highest priority (lowest value), it > doesn't help to disable cache_trim_mode. Yes, right. Lemme think it more and apply the consideration. > And, please take care of other "break" in the loop, for example, if > kthread_should_stop(), etc. I will. Thank you. Byungchul > -- > Best Regards, > Huang, Ying > > > 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