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s=arc-20220608; d=hostedemail.com; t=1709613198; a=rsa-sha256; cv=none; b=intm0tETTNc8OO/3W8mZhgO7den2LWVzOXPbBDhx4QW7BGQdhL2S86udbgjWtgdXkvaUGG 5/XShJchvxmsQAAkvPn+TCg5VvwRdISmhaiRDZBDdE/Ulw7tpbDn9yMzUFtg6qCrw404/r TLDnu3GUgVLAbsuco6r5qmKJUjmQexk= ARC-Authentication-Results: i=1; imf17.hostedemail.com; dkim=none; spf=temperror (imf17.hostedemail.com: error in processing during lookup of byungchul@sk.com: DNS error) smtp.mailfrom=byungchul@sk.com; dmarc=temperror reason="server fail" header.from=sk.com (policy=temperror) X-AuditID: a67dfc5b-d6dff70000001748-57-65e6a086aa89 Date: Tue, 5 Mar 2024 13:33:05 +0900 From: Byungchul Park To: akpm@linux-foundation.org Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, kernel_team@skhynix.com, yuzhao@google.com, ying.huang@intel.com, hannes@cmpxchg.org Subject: Re: [PATCH v6] mm, vmscan: retry kswapd's priority loop with cache_trim_mode off on failure Message-ID: <20240305043305.GB21107@system.software.com> References: <20240304033611.GD13332@system.software.com> <20240304082118.20499-1-byungchul@sk.com> MIME-Version: 1.0 Content-Type: text/plain; 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Make it retry the kswapd's scan priority loop with > cache_trim_mode off *only if* the mode didn't work in the > previous loop. (feedbacked by Huang Ying) > 2. Take into account 'break's from the priority loop when making > the decision whether to retry. (feedbacked by Huang Ying) > 3. Update the test result in the commit message. > > 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 f811ee583158fd53d0e94d32ce5948fac4b17cfe Mon Sep 17 00:00:00 2001 > From: Byungchul Park > Date: Mon, 4 Mar 2024 15:27:37 +0900 > Subject: [PATCH v6] 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 | 1664772 | > | nr_active_anon | 1780700 | 437834 | > | nr_inactive_file | 30425 | 40882 | > | nr_active_file | 14961 | 3012 | > | pgpromote_success | 356 | 1293122 | > | pgpromote_candidate | 21953245 | 1824148 | > | pgactivate | 1844523 | 3311907 | > | pgdeactivate | 50634 | 1554069 | > | pgfault | 31100294 | 6518806 | > | pgdemote_kswapd | 30856 | 2230821 | > | pgscan_kswapd | 1861981 | 7667629 | > | pgscan_anon | 1822930 | 7610583 | > | pgscan_file | 39051 | 57046 | > | pgsteal_anon | 386 | 2192033 | > | pgsteal_file | 30470 | 38788 | > | pageoutrun | 30 | 412 | > | numa_hint_faults | 27418279 | 2875955 | > | numa_pages_migrated | 356 | 1293122 | > +-----------------------+-------------------------------+ > > Signed-off-by: Byungchul Park > --- > mm/vmscan.c | 21 ++++++++++++++++++++- > 1 file changed, 20 insertions(+), 1 deletion(-) > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index bba207f41b14..6fe45eca7766 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -108,6 +108,12 @@ struct scan_control { > /* Can folios be swapped as part of reclaim? */ > unsigned int may_swap:1; > > + /* Not allow cache_trim_mode to be turned on as part of reclaim? */ > + unsigned int no_cache_trim_mode:1; > + > + /* Has cache_trim_mode failed at least once? */ > + unsigned int cache_trim_mode_failed:1; > + > /* Proactive reclaim invoked by userspace through memory.reclaim */ > unsigned int proactive:1; > > @@ -2268,7 +2274,8 @@ 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->no_cache_trim_mode) > sc->cache_trim_mode = 1; > else > sc->cache_trim_mode = 0; > @@ -5967,6 +5974,8 @@ static void shrink_node(pg_data_t *pgdat, struct scan_control *sc) > */ > if (reclaimable) > pgdat->kswapd_failures = 0; > + else if (sc->cache_trim_mode) > + sc->cache_trim_mode_failed = 1; > } > > /* > @@ -6898,6 +6907,16 @@ static int balance_pgdat(pg_data_t *pgdat, int order, int highest_zoneidx) > sc.priority--; > } while (sc.priority >= 1); > > + /* > + * Restart only if it went through the priority loop all the way, > + * but cache_trim_mode didn't work. > + */ > + if (!sc.nr_reclaimed && sc.priority < 1 && > + !sc.no_cache_trim_mode && sc.cache_trim_mode_failed) { > + sc.no_cache_trim_mode = 1; > + goto restart; > + } > + > if (!sc.nr_reclaimed) > pgdat->kswapd_failures++; Or 's/cache_trim_mode_failed/balancing_cleverness_failed' so that any balancing cleverness can be surpressed when needed? Even though I faced an issue by cache_trim_mode and I'm trying to resolve it this time, but I'm still not sure if kswapd's reclaim is okay with other cleverness(?) including SCAN_FRACT at its highest priority. Just grumbling. You can ignore the second paragrph :( Byungchul