From: Marcelo Tosatti <mtosatti@redhat.com>
To: Christoph Lameter <cl@linux.com>
Cc: Aaron Tomlin <atomlin@atomlin.com>,
Frederic Weisbecker <frederic@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
Russell King <linux@armlinux.org.uk>,
Huacai Chen <chenhuacai@kernel.org>,
Heiko Carstens <hca@linux.ibm.com>,
x86@kernel.org, Vlastimil Babka <vbabka@suse.cz>,
Michal Hocko <mhocko@suse.com>,
Marcelo Tosatti <mtosatti@redhat.com>
Subject: [PATCH v8 01/13] vmstat: allow_direct_reclaim should use zone_page_state_snapshot
Date: Mon, 15 May 2023 15:00:16 -0300 [thread overview]
Message-ID: <20230515180138.442505633@redhat.com> (raw)
In-Reply-To: 20230515180015.016409657@redhat.com
A customer provided evidence indicating that a process
was stalled in direct reclaim:
- The process was trapped in throttle_direct_reclaim().
The function wait_event_killable() was called to wait condition
allow_direct_reclaim(pgdat) for current node to be true.
The allow_direct_reclaim(pgdat) examined the number of free pages
on the node by zone_page_state() which just returns value in
zone->vm_stat[NR_FREE_PAGES].
- On node #1, zone->vm_stat[NR_FREE_PAGES] was 0.
However, the freelist on this node was not empty.
- This inconsistent of vmstat value was caused by percpu vmstat on
nohz_full cpus. Every increment/decrement of vmstat is performed
on percpu vmstat counter at first, then pooled diffs are cumulated
to the zone's vmstat counter in timely manner. However, on nohz_full
cpus (in case of this customer's system, 48 of 52 cpus) these pooled
diffs were not cumulated once the cpu had no event on it so that
the cpu started sleeping infinitely.
I checked percpu vmstat and found there were total 69 counts not
cumulated to the zone's vmstat counter yet.
- In this situation, kswapd did not help the trapped process.
In pgdat_balanced(), zone_wakermark_ok_safe() examined the number
of free pages on the node by zone_page_state_snapshot() which
checks pending counts on percpu vmstat.
Therefore kswapd could know there were 69 free pages correctly.
Since zone->_watermark = {8, 20, 32}, kswapd did not work because
69 was greater than 32 as high watermark.
Change allow_direct_reclaim to use zone_page_state_snapshot, which
allows a more precise version of the vmstat counters to be used.
allow_direct_reclaim will only be called from try_to_free_pages,
which is not a hot path.
Suggested-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
---
Index: linux-vmstat-remote/mm/vmscan.c
===================================================================
--- linux-vmstat-remote.orig/mm/vmscan.c
+++ linux-vmstat-remote/mm/vmscan.c
@@ -6886,7 +6886,7 @@ static bool allow_direct_reclaim(pg_data
continue;
pfmemalloc_reserve += min_wmark_pages(zone);
- free_pages += zone_page_state(zone, NR_FREE_PAGES);
+ free_pages += zone_page_state_snapshot(zone, NR_FREE_PAGES);
}
/* If there are no reserves (unexpected config) then do not throttle */
next prev parent reply other threads:[~2023-05-15 18:07 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-05-15 18:00 [PATCH v8 00/13] fold per-CPU vmstats remotely Marcelo Tosatti
2023-05-15 18:00 ` Marcelo Tosatti [this message]
2023-05-24 12:34 ` [PATCH v8 01/13] vmstat: allow_direct_reclaim should use zone_page_state_snapshot Michal Hocko
2023-05-25 7:05 ` Aaron Tomlin
2023-05-15 18:00 ` [PATCH v8 02/13] this_cpu_cmpxchg: ARM64: switch this_cpu_cmpxchg to locked, add _local function Marcelo Tosatti
2023-05-15 18:00 ` [PATCH v8 03/13] this_cpu_cmpxchg: loongarch: " Marcelo Tosatti
2023-05-15 18:00 ` [PATCH v8 04/13] this_cpu_cmpxchg: S390: " Marcelo Tosatti
2023-05-15 18:00 ` [PATCH v8 05/13] this_cpu_cmpxchg: x86: " Marcelo Tosatti
2023-05-15 18:00 ` [PATCH v8 06/13] add this_cpu_cmpxchg_local and asm-generic definitions Marcelo Tosatti
2023-05-15 18:00 ` [PATCH v8 07/13] convert this_cpu_cmpxchg users to this_cpu_cmpxchg_local Marcelo Tosatti
2023-05-15 18:00 ` [PATCH v8 08/13] mm/vmstat: switch counter modification to cmpxchg Marcelo Tosatti
2023-05-15 18:00 ` [PATCH v8 09/13] vmstat: switch per-cpu vmstat counters to 32-bits Marcelo Tosatti
2023-05-15 18:00 ` [PATCH v8 10/13] mm/vmstat: use xchg in cpu_vm_stats_fold Marcelo Tosatti
2023-05-15 18:00 ` [PATCH v8 11/13] mm/vmstat: switch vmstat shepherd to flush per-CPU counters remotely Marcelo Tosatti
2023-05-15 18:00 ` [PATCH v8 12/13] mm/vmstat: refresh stats remotely instead of via work item Marcelo Tosatti
2023-05-15 18:00 ` [PATCH v8 13/13] vmstat: add pcp remote node draining via cpu_vm_stats_fold Marcelo Tosatti
2023-05-16 8:09 ` [PATCH v8 00/13] fold per-CPU vmstats remotely Christoph Lameter
2023-05-16 18:02 ` Marcelo Tosatti
2023-05-24 12:51 ` Michal Hocko
2023-05-24 13:53 ` Marcelo Tosatti
2023-05-25 6:47 ` Michal Hocko
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20230515180138.442505633@redhat.com \
--to=mtosatti@redhat.com \
--cc=akpm@linux-foundation.org \
--cc=atomlin@atomlin.com \
--cc=chenhuacai@kernel.org \
--cc=cl@linux.com \
--cc=frederic@kernel.org \
--cc=hca@linux.ibm.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=linux@armlinux.org.uk \
--cc=mhocko@suse.com \
--cc=vbabka@suse.cz \
--cc=x86@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.