+ mm-fix-draining-remote-pageset.patch added to mm-unstable branch

+ mm-fix-draining-remote-pageset.patch added to mm-unstable branch

[Andrew Morton]

The patch titled
     Subject: mm: fix draining remote pageset
has been added to the -mm mm-unstable branch.  Its filename is
     mm-fix-draining-remote-pageset.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-fix-draining-remote-pageset.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Huang Ying <ying.huang@intel.com>
Subject: mm: fix draining remote pageset
Date: Fri, 11 Aug 2023 17:08:19 +0800

If there is no memory allocation/freeing in the remote pageset after
some time (3 seconds for now), the remote pageset will be drained to
avoid memory wastage.

But in the current implementation, vmstat updater worker may not be
re-queued when we are waiting for the timeout (pcp->expire != 0) if
there are no vmstat changes, for example, when CPU goes idle.

This is fixed via guaranteeing that the vmstat updater worker will
always be re-queued when we are waiting for the timeout.

We can reproduce the bug via allocating/freeing pages from remote
node, then go idle.  And the patch can fix it.

- Run some workloads, use `numactl` to bind CPU to node 0 and memory to
  node 1.  So the PCP of the CPU on node 0 for zone on node 1 will be
  filled.

- After workloads finish, idle for 60s

- Check /proc/zoneinfo

With the original kernel, the number of pages in the PCP of the CPU on
node 0 for zone on node 1 is non-zero after idle.  With the patched
kernel, that becomes 0 after idle.  We avoid to keep pages in the remote
PCP during idle.

Christoph added:

: Having some pages from a remote NUMA node stuck in a pcp somewhere is 
: making that memory unusable. It is usually rate that these remote pages 
: are needed again and so they may remain there for a long time if the 
: situation is right.

Link: https://lkml.kernel.org/r/20230811090819.60845-1-ying.huang@intel.com
Fixes: 7cc36bbddde5 ("vmstat: on-demand vmstat workers V8")
Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
Reviewed-by: Christoph Lameter <cl@linux.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Michal Hocko <mhocko@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/vmstat.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/mm/vmstat.c~mm-fix-draining-remote-pageset
+++ a/mm/vmstat.c
@@ -855,8 +855,10 @@ static int refresh_cpu_vm_stats(bool do_
 				continue;
 			}
 
-			if (__this_cpu_dec_return(pcp->expire))
+			if (__this_cpu_dec_return(pcp->expire)) {
+				changes++;
 				continue;
+			}
 
 			if (__this_cpu_read(pcp->count)) {
 				drain_zone_pages(zone, this_cpu_ptr(pcp));
_

Patches currently in -mm which might be from ying.huang@intel.com are

memory-tiering-add-abstract-distance-calculation-algorithms-management.patch
acpi-hmat-refactor-hmat_register_target_initiators.patch
acpi-hmat-calculate-abstract-distance-with-hmat.patch
dax-kmem-calculate-abstract-distance-with-general-interface.patch
mm-fix-draining-remote-pageset.patch