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Mon, 26 Feb 2024 13:06:42 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id 5b8mMuKM3GWQWAAAD6G6ig (envelope-from ); Mon, 26 Feb 2024 13:06:42 +0000 Date: Mon, 26 Feb 2024 14:06:30 +0100 From: Michal Hocko To: Byungchul Park Cc: akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, kernel_team@skhynix.com, yuzhao@google.com, ying.huang@intel.com, Mel Gorman , Vlastimil Babka , Johannes Weiner Subject: Re: [PATCH v3] mm, vmscan: do not turn on cache_trim_mode if it doesn't work Message-ID: References: <20240223054407.14829-1-byungchul@sk.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240223054407.14829-1-byungchul@sk.com> Authentication-Results: smtp-out2.suse.de; none X-Spamd-Result: default: False [-2.60 / 50.00]; ARC_NA(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; MIME_GOOD(-0.10)[text/plain]; RCVD_COUNT_THREE(0.00)[3]; DKIM_SIGNED(0.00)[suse.com:s=susede1]; RCPT_COUNT_SEVEN(0.00)[10]; FUZZY_BLOCKED(0.00)[rspamd.com]; FROM_EQ_ENVFROM(0.00)[]; MIME_TRACE(0.00)[0:+]; MID_RHS_NOT_FQDN(0.50)[]; RCVD_TLS_ALL(0.00)[]; BAYES_HAM(-3.00)[100.00%] X-Spam-Level: X-Spam-Flag: NO X-Spam-Score: -2.60 [CC Mel, Vlastimil and Johannes for awareness] On Fri 23-02-24 14:44:07, Byungchul Park wrote: > 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 05846e34bf02ac9b3e254324dc2d7afd97a025d9 Mon Sep 17 00:00:00 2001 > From: Byungchul Park > Date: Fri, 23 Feb 2024 13:47:16 +0900 > Subject: [PATCH v3] mm, vmscan: do not turn on cache_trim_mode if it doesn't work > > 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 leads kswapd_failures to reach MAX_RECLAIM_RETRIES and > stopping kswapd from functioning until direct reclaim eventually works > to resume kswapd. > > So do not turn on cache_trim_mode if the mode doesn't work, especially > while the sytem is struggling against 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 | 1636737 | > | nr_active_anon | 1780700 | 465913 | > | nr_inactive_file | 30425 | 35711 | > | nr_active_file | 14961 | 8698 | > | pgpromote_success | 356 | 1267785 | > | pgpromote_candidate | 21953245 | 1745631 | > | pgactivate | 1844523 | 3309867 | > | pgdeactivate | 50634 | 1545041 | > | pgfault | 31100294 | 6411036 | > | pgdemote_kswapd | 30856 | 2267467 | > | pgscan_kswapd | 1861981 | 7729231 | > | pgscan_anon | 1822930 | 7667544 | > | pgscan_file | 39051 | 61687 | > | pgsteal_anon | 386 | 2227217 | > | pgsteal_file | 30470 | 40250 | > | pageoutrun | 30 | 457 | > | numa_hint_faults | 27418279 | 2752289 | > | numa_pages_migrated | 356 | 1267785 | > +-----------------------+-------------------------------+ > > Signed-off-by: Byungchul Park > --- > mm/vmscan.c | 24 +++++++++++++++++++----- > 1 file changed, 19 insertions(+), 5 deletions(-) > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index bba207f41b14..f7312d831fed 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -127,6 +127,9 @@ struct scan_control { > /* One of the zones is ready for compaction */ > unsigned int compaction_ready:1; > > + /* If the last try was reclaimable */ > + unsigned int reclaimable:1; > + > /* There is easily reclaimable cold cache in the current node */ > unsigned int cache_trim_mode:1; > > @@ -2266,9 +2269,14 @@ 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. > + * > + * It doesn't make sense to keep cache_trim_mode on if the mode > + * is not working while struggling against reclaim. So do not > + * turn it on if so. Note the highest priority of kswapd is 1. > */ > 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->cache_trim_mode && !sc->reclaimable && sc->priority <= 1)) > sc->cache_trim_mode = 1; > else > sc->cache_trim_mode = 0; > @@ -5862,7 +5870,6 @@ static void shrink_node(pg_data_t *pgdat, struct scan_control *sc) > { > unsigned long nr_reclaimed, nr_scanned, nr_node_reclaimed; > struct lruvec *target_lruvec; > - bool reclaimable = false; > > if (lru_gen_enabled() && root_reclaim(sc)) { > lru_gen_shrink_node(pgdat, sc); > @@ -5877,6 +5884,14 @@ static void shrink_node(pg_data_t *pgdat, struct scan_control *sc) > nr_reclaimed = sc->nr_reclaimed; > nr_scanned = sc->nr_scanned; > > + /* > + * Reset to the default values at the start. > + */ > + if (sc->priority == DEF_PRIORITY) { > + sc->reclaimable = 1; > + sc->cache_trim_mode = 0; > + } > + > prepare_scan_control(pgdat, sc); > > shrink_node_memcgs(pgdat, sc); > @@ -5890,8 +5905,7 @@ static void shrink_node(pg_data_t *pgdat, struct scan_control *sc) > vmpressure(sc->gfp_mask, sc->target_mem_cgroup, true, > sc->nr_scanned - nr_scanned, nr_node_reclaimed); > > - if (nr_node_reclaimed) > - reclaimable = true; > + sc->reclaimable = !!nr_node_reclaimed; > > if (current_is_kswapd()) { > /* > @@ -5965,7 +5979,7 @@ static void shrink_node(pg_data_t *pgdat, struct scan_control *sc) > * sleep. On reclaim progress, reset the failure counter. A > * successful direct reclaim run will revive a dormant kswapd. > */ > - if (reclaimable) > + if (sc->reclaimable) > pgdat->kswapd_failures = 0; > } > > -- > 2.17.1 > -- Michal Hocko SUSE Labs