Byungchul Park <byungchul@xxxxxx> writes: > On Thu, Feb 22, 2024 at 06:49:00PM +0900, Byungchul Park wrote: >> On Thu, Feb 22, 2024 at 06:20:42PM +0900, Byungchul Park wrote: >> > On Thu, Feb 22, 2024 at 04:37:16PM +0800, Huang, Ying wrote: >> > > Byungchul Park <byungchul@xxxxxx> writes: >> > > >> > > > 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 07e0baab368160e50b6ca35d95745168aa60e217 Mon Sep 17 00:00:00 2001 >> > > > From: Byungchul Park <byungchul@xxxxxx> >> > > > Date: Thu, 22 Feb 2024 14:50:17 +0900 >> > > > Subject: [PATCH v2] mm, vmscan: don't turn on cache_trim_mode at high scan priorities >> > > > >> > > > With cache_trim_mode on, reclaim logic doesn't bother reclaiming anon >> > > > pages. However, it should be more careful to turn on 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 can lead kswapd_failures to reach MAX_RECLAIM_RETRIES and >> > > > stopping kswapd until direct reclaim eventually works to resume kswapd. >> > > > So this is more like a bug fix than a performance improvement. >> > > > >> > > > 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 kswapd stops. >> > > > >> > > > With this, you could eventually 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: >> > > > >> > > > -nr_inactive_anon 321935 >> > > > -nr_active_anon 1780700 >> > > > -nr_inactive_file 30425 >> > > > -nr_active_file 14961 >> > > > -pgpromote_success 356 >> > > > -pgpromote_candidate 21953245 >> > > > -pgactivate 1844523 >> > > > -pgdeactivate 50634 >> > > > -pgfault 31100294 >> > > > -pgdemote_kswapd 30856 >> > > > -pgscan_kswapd 1861981 >> > > > -pgscan_anon 1822930 >> > > > -pgscan_file 39051 >> > > > -pgsteal_anon 386 >> > > > -pgsteal_file 30470 >> > > > -pageoutrun 30 >> > > > -numa_hint_faults 27418279 >> > > > -numa_pages_migrated 356 >> > > > >> > > > +nr_inactive_anon 1662306 >> > > > +nr_active_anon 440303 >> > > > +nr_inactive_file 27669 >> > > > +nr_active_file 1654 >> > > > +pgpromote_success 1314102 >> > > > +pgpromote_candidate 1892525 >> > > > +pgactivate 3284457 >> > > > +pgdeactivate 1527504 >> > > > +pgfault 6847775 >> > > > +pgdemote_kswapd 2142047 >> > > > +pgscan_kswapd 7496588 >> > > > +pgscan_anon 7462488 >> > > > +pgscan_file 34100 >> > > > +pgsteal_anon 2115661 >> > > > +pgsteal_file 26386 >> > > > +pageoutrun 378 >> > > > +numa_hint_faults 3220891 >> > > > +numa_pages_migrated 1314102 >> > > > >> > > > where -: before this patch, +: after this patch >> > > > >> > > > Signed-off-by: Byungchul Park <byungchul@xxxxxx> >> > > > --- >> > > > mm/vmscan.c | 10 +++++++++- >> > > > 1 file changed, 9 insertions(+), 1 deletion(-) >> > > > >> > > > diff --git a/mm/vmscan.c b/mm/vmscan.c >> > > > index bba207f41b14..6eda59fce5ee 100644 >> > > > --- a/mm/vmscan.c >> > > > +++ b/mm/vmscan.c >> > > > @@ -2266,9 +2266,17 @@ static void prepare_scan_control(pg_data_t *pgdat, struct scan_control *sc) >> > > > * If we have plenty of inactive file pages that aren't >> > > > * thrashing, try to reclaim those first before touching >> > > > * anonymous pages. >> > > > + * >> > > > + * However, the condition 'sc->cache_trim_mode == 1' all through >> > > > + * the scan priorties might lead reclaim failure. If it keeps >> > > > + * MAX_RECLAIM_RETRIES times, then kswapd would get stopped even >> > > > + * if there are still plenty anon pages to reclaim, which is not >> > > > + * desirable. So do not use cache_trim_mode when reclaim is not >> > > > + * smooth e.i. high scan priority. >> > > > */ >> > > > file = lruvec_page_state(target_lruvec, NR_INACTIVE_FILE); >> > > > - if (file >> sc->priority && !(sc->may_deactivate & DEACTIVATE_FILE)) >> > > > + if (sc->priority > 1 && file >> sc->priority && >> > > > + !(sc->may_deactivate & DEACTIVATE_FILE)) >> > > > sc->cache_trim_mode = 1; >> > > > else >> > > > sc->cache_trim_mode = 0; >> > > >> > > In get_scan_count(), there's following code, >> > > >> > > /* >> > > * Do not apply any pressure balancing cleverness when the >> > > * system is close to OOM, scan both anon and file equally >> > > * (unless the swappiness setting disagrees with swapping). >> > > */ >> > > if (!sc->priority && swappiness) { >> > > scan_balance = SCAN_EQUAL; >> > > goto out; >> > > } >> > > >> > > So, swappiness is 0 in you system? Please check it. If it's not 0, >> > > please check why this doesn't help. >> > >> > Nice information! Then the change should be: >> > >> > diff --git a/mm/vmscan.c b/mm/vmscan.c >> > index bba207f41b14..91f9bab86e92 100644 >> > --- a/mm/vmscan.c >> > +++ b/mm/vmscan.c >> > @@ -2357,7 +2357,7 @@ static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc, >> > * system is close to OOM, scan both anon and file equally >> > * (unless the swappiness setting disagrees with swapping). >> > */ >> > - if (!sc->priority && swappiness) { >> > + if (sc->priority <= 1 && swappiness) { >> > scan_balance = SCAN_EQUAL; >> > goto out; >> > } >> >> Or: >> >> diff --git a/mm/vmscan.c b/mm/vmscan.c >> index bba207f41b14..c54371a398b1 100644 >> --- a/mm/vmscan.c >> +++ b/mm/vmscan.c >> @@ -6896,7 +6896,7 @@ static int balance_pgdat(pg_data_t *pgdat, int order, int highest_zoneidx) >> >> if (raise_priority || !nr_reclaimed) >> sc.priority--; >> - } while (sc.priority >= 1); >> + } while (sc.priority >= 0); >> >> if (!sc.nr_reclaimed) >> pgdat->kswapd_failures++; > > +cc Mel Gorman > > I just found this was intended. See commit 9aa41348a8d11 ("mm: vmscan: > do not allow kswapd to scan at maximum priority"). Mel Gorman didn't want > to make kswapd too much aggressive. However, does it make sense to stop > kswapd even if there are plenty cold anon pages to reclaim and make the > system wait for direct reclaim? Maybe we can play with cache_trim_mode, for example, if sc.nr_reclaimed == 0 and sc.cache_trim_mode == true, force disabling cache_trim_mode in the next round? -- Best Regards, Huang, Ying > Thoughts? > > Byungchul > >> --- >> >> Byungchul >> >> > Worth noting that the priority goes from DEF_PRIORITY to 1 in >> > balance_pgdat() of kswapd. I will change how to fix to this if this >> > looks more reasonable. >> > >> > Byungchul