The patch titled
Subject: mm/swap, workingset: make anon shadow nodes memcg aware
has been added to the -mm mm-unstable branch. Its filename is
mm-swap-workingset-make-anon-shadow-nodes-memcg-aware.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-swap-workingset-make-anon-shadow-nodes-memcg-aware.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: Kairui Song <kasong@xxxxxxxxxxx>
Subject: mm/swap, workingset: make anon shadow nodes memcg aware
Date: Tue, 20 Aug 2024 17:23:59 +0800
Currently, the workingset (shadow) nodes of the swap cache are not
accounted to their corresponding memory cgroup, instead, they are all
accounted to the root cgroup. This leads to inaccurate accounting and
ineffective reclaiming. One cgroup could swap out a large amount of
memory, take up a large amount of memory with shadow nodes without being
accounted.
This issue is similar to commit 7b785645e8f1 ("mm: fix page cache
convergence regression"), where page cache shadow nodes were incorrectly
accounted. That was due to the accidental dropping of the accounting flag
during the XArray conversion in commit a28334862993 ("page cache: Finish
XArray conversion").
However, this fix has a different cause. Swap cache shadow nodes were
never accounted even before the XArray conversion, since they did not
exist until commit 3852f6768ede ("mm/swapcache: support to handle the
shadow entries"), which was years after the XArray conversion.
It's worth noting that one anon shadow Xarray node may contain different
entries from different cgroup, and it gets accounted at reclaim time, so
it's arguable which cgroup it should be accounted to (as Shakeal Butt
pointed out [1]). File pages may suffer similar issue but less common.
Things like proactive memory reclaim could make thing more complex.
So this commit still can't provide a 100% accurate accounting of anon
shadows, but it covers the cases when one memory cgroup uses significant
amount of swap, and in most cases memory pressure in one cgroup only
suppose to reclaim this cgroup and children. Besides, this fix is clean
and easy enough.
Link: https://lore.kernel.org/all/7gzevefivueqtebzvikzbucnrnpurmh3scmfuiuo2tnrs37xso@haj7gzepjur2/ [1]
Link: https://lkml.kernel.org/r/20240820092359.97782-1-ryncsn@xxxxxxxxx
Signed-off-by: Kairui Song <kasong@xxxxxxxxxxx>
Cc: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx>
Cc: Chris Li <chrisl@xxxxxxxxxx>
Cc: "Huang, Ying" <ying.huang@xxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Muchun Song <muchun.song@xxxxxxxxx>
Cc: Nhat Pham <nphamcs@xxxxxxxxx>
Cc: Roman Gushchin <roman.gushchin@xxxxxxxxx>
Cc: Shakeel Butt <shakeel.butt@xxxxxxxxx>
Cc: Yosry Ahmed <yosryahmed@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/swap_state.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
--- a/mm/swap_state.c~mm-swap-workingset-make-anon-shadow-nodes-memcg-aware
+++ a/mm/swap_state.c
@@ -97,6 +97,7 @@ int add_to_swap_cache(struct folio *foli
void *old;
xas_set_update(&xas, workingset_update_node);
+ xas_set_lru(&xas, &shadow_nodes);
VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
VM_BUG_ON_FOLIO(folio_test_swapcache(folio), folio);
@@ -718,7 +719,7 @@ int init_swap_address_space(unsigned int
return -ENOMEM;
for (i = 0; i < nr; i++) {
space = spaces + i;
- xa_init_flags(&space->i_pages, XA_FLAGS_LOCK_IRQ);
+ xa_init_flags(&space->i_pages, XA_FLAGS_LOCK_IRQ | XA_FLAGS_ACCOUNT);
atomic_set(&space->i_mmap_writable, 0);
space->a_ops = &swap_aops;
/* swap cache doesn't use writeback related tags */
_
Patches currently in -mm which might be from kasong@xxxxxxxxxxx are
mm-swap-clean-up-initialization-helper.patch
mm-swap-skip-slot-cache-on-freeing-for-mthp.patch
mm-swap-allow-cache-reclaim-to-skip-slot-cache.patch
mm-swap-add-a-fragment-cluster-list.patch
mm-swap-relaim-the-cached-parts-that-got-scanned.patch
mm-swap-add-a-adaptive-full-cluster-cache-reclaim.patch
mm-swap-workingset-make-anon-shadow-nodes-memcg-aware.patch
