The patch titled
Subject: mm: skip reclaiming folios in legacy memcg writeback indeterminate contexts
has been added to the -mm mm-unstable branch. Its filename is
mm-skip-reclaiming-folios-in-legacy-memcg-writeback-indeterminate-contexts.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-skip-reclaiming-folios-in-legacy-memcg-writeback-indeterminate-contexts.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: Joanne Koong <joannelkoong@xxxxxxxxx>
Subject: mm: skip reclaiming folios in legacy memcg writeback indeterminate contexts
Date: Fri, 22 Nov 2024 15:23:56 -0800
Currently in shrink_folio_list(), reclaim for folios under writeback falls
into 3 different cases:
1) Reclaim is encountering an excessive number of folios under
writeback and this folio has both the writeback and reclaim flags
set
2) Dirty throttling is enabled (this happens if reclaim through cgroup
is not enabled, if reclaim through cgroupv2 memcg is enabled, or
if reclaim is on the root cgroup), or if the folio is not marked for
immediate reclaim, or if the caller does not have __GFP_FS (or
__GFP_IO if it's going to swap) set
3) Legacy cgroupv1 encounters a folio that already has the reclaim flag
set and the caller did not have __GFP_FS (or __GFP_IO if swap) set
In cases 1) and 2), we activate the folio and skip reclaiming it while in
case 3), we wait for writeback to finish on the folio and then try to
reclaim the folio again. In case 3, we wait on writeback because cgroupv1
does not have dirty folio throttling, as such this is a mitigation against
the case where there are too many folios in writeback with nothing else to
reclaim.
For filesystems where writeback may take an indeterminate amount of time
to write to disk, this has the possibility of stalling reclaim.
In this commit, if legacy memcg encounters a folio with the reclaim flag
set (eg case 3) and the folio belongs to a mapping that has the
AS_WRITEBACK_INDETERMINATE flag set, the folio will be activated and skip
reclaim (eg default to behavior in case 2) instead.
Link: https://lkml.kernel.org/r/20241122232359.429647-3-joannelkoong@xxxxxxxxx
Signed-off-by: Joanne Koong <joannelkoong@xxxxxxxxx>
Reviewed-by: Shakeel Butt <shakeel.butt@xxxxxxxxx>
Acked-by: Miklos Szeredi <mszeredi@xxxxxxxxxx>
Cc: Bernd Schubert <bernd.schubert@xxxxxxxxxxx>
Cc: Jingbo Xu <jefflexu@xxxxxxxxxxxxxxxxx>
Cc: Josef Bacik <josef@xxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/vmscan.c | 10 +++++++---
1 file changed, 7 insertions(+), 3 deletions(-)
--- a/mm/vmscan.c~mm-skip-reclaiming-folios-in-legacy-memcg-writeback-indeterminate-contexts
+++ a/mm/vmscan.c
@@ -1165,8 +1165,9 @@ retry:
* 2) Global or new memcg reclaim encounters a folio that is
* not marked for immediate reclaim, or the caller does not
* have __GFP_FS (or __GFP_IO if it's simply going to swap,
- * not to fs). In this case mark the folio for immediate
- * reclaim and continue scanning.
+ * not to fs), or the writeback may take an indeterminate
+ * amount of time to complete. In this case mark the folio
+ * for immediate reclaim and continue scanning.
*
* Require may_enter_fs() because we would wait on fs, which
* may not have submitted I/O yet. And the loop driver might
@@ -1191,6 +1192,8 @@ retry:
* takes to write them to disk.
*/
if (folio_test_writeback(folio)) {
+ mapping = folio_mapping(folio);
+
/* Case 1 above */
if (current_is_kswapd() &&
folio_test_reclaim(folio) &&
@@ -1201,7 +1204,8 @@ retry:
/* Case 2 above */
} else if (writeback_throttling_sane(sc) ||
!folio_test_reclaim(folio) ||
- !may_enter_fs(folio, sc->gfp_mask)) {
+ !may_enter_fs(folio, sc->gfp_mask) ||
+ (mapping && mapping_writeback_indeterminate(mapping))) {
/*
* This is slightly racy -
* folio_end_writeback() might have
_
Patches currently in -mm which might be from joannelkoong@xxxxxxxxx are
mm-add-as_writeback_indeterminate-mapping-flag.patch
mm-skip-reclaiming-folios-in-legacy-memcg-writeback-indeterminate-contexts.patch
fs-writeback-in-wait_sb_inodes-skip-wait-for-as_writeback_indeterminate-mappings.patch
mm-migrate-skip-migrating-folios-under-writeback-with-as_writeback_indeterminate-mappings.patch
fuse-remove-tmp-folio-for-writebacks-and-internal-rb-tree.patch
