The patch titled
Subject: mm/vmscan: use PG_dropbehind instead of PG_reclaim in shrink_folio_list()
has been added to the -mm mm-unstable branch. Its filename is
mm-vmscan-use-pg_dropbehind-instead-of-pg_reclaim-in-shrink_folio_list.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-vmscan-use-pg_dropbehind-instead-of-pg_reclaim-in-shrink_folio_list.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: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
Subject: mm/vmscan: use PG_dropbehind instead of PG_reclaim in shrink_folio_list()
Date: Thu, 30 Jan 2025 12:00:45 +0200
The recently introduced PG_dropbehind allows for freeing folios
immediately after writeback. Unlike PG_reclaim, it does not need vmscan
to be involved to get the folio freed.
Instead of using folio_set_reclaim(), use folio_set_dropbehind() in
shrink_folio_list().
It is safe to leave PG_dropbehind on the folio if, for some reason (bug?),
the folio is not in a writeback state after ->writepage(). In these
cases, the kernel had to clear PG_reclaim as it shared a page flag bit
with PG_readahead.
Also use PG_dropbehind instead PG_reclaim to detect I/O congestion.
Link: https://lkml.kernel.org/r/20250130100050.1868208-8-kirill.shutemov@xxxxxxxxxxxxxxx
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Acked-by: David Hildenbrand <david@xxxxxxxxxx>
Cc: Andi Shyti <andi.shyti@xxxxxxxxxxxxxxx>
Cc: Chengming Zhou <chengming.zhou@xxxxxxxxx>
Cc: Christian Brauner <brauner@xxxxxxxxxx>
Cc: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
Cc: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
Cc: Dave Airlie <airlied@xxxxxxxxx>
Cc: gehao <gehao@xxxxxxxxxx>
Cc: Jani Nikula <jani.nikula@xxxxxxxxxxxxxxx>
Cc: Jason A. Donenfeld <jason@xxxxxxxxx>
Cc: Jens Axboe <axboe@xxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Jonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx>
Cc: Josef Bacik <josef@xxxxxxxxxxxxxx>
Cc: "Masami Hiramatsu (Google)" <mhiramat@xxxxxxxxxx>
Cc: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
Cc: Mattew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Miklos Szeredi <miklos@xxxxxxxxxx>
Cc: Nhat Pham <nphamcs@xxxxxxxxx>
Cc: Oscar Salvador <osalvador@xxxxxxx>
Cc: Ran Xiaokai <ran.xiaokai@xxxxxxxxxx>
Cc: Rodrigo Vivi <rodrigo.vivi@xxxxxxxxx>
Cc: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
Cc: Tvrtko Ursulin <tursulin@xxxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Yosry Ahmed <yosryahmed@xxxxxxxxxx>
Cc: Yu Zhao <yuzhao@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/vmscan.c | 30 ++++++++----------------------
1 file changed, 8 insertions(+), 22 deletions(-)
--- a/mm/vmscan.c~mm-vmscan-use-pg_dropbehind-instead-of-pg_reclaim-in-shrink_folio_list
+++ a/mm/vmscan.c
@@ -1140,7 +1140,7 @@ retry:
* for immediate reclaim are making it to the end of
* the LRU a second time.
*/
- if (writeback && folio_test_reclaim(folio))
+ if (writeback && folio_test_dropbehind(folio))
stat->nr_congested += nr_pages;
/*
@@ -1149,7 +1149,7 @@ retry:
*
* 1) If reclaim is encountering an excessive number
* of folios under writeback and this folio has both
- * the writeback and reclaim flags set, then it
+ * the writeback and dropbehind flags set, then it
* indicates that folios are being queued for I/O but
* are being recycled through the LRU before the I/O
* can complete. Waiting on the folio itself risks an
@@ -1173,7 +1173,7 @@ retry:
* would probably show more reasons.
*
* 3) Legacy memcg encounters a folio that already has the
- * reclaim flag set. memcg does not have any dirty folio
+ * dropbehind flag set. memcg does not have any dirty folio
* throttling so we could easily OOM just because too many
* folios are in writeback and there is nothing else to
* reclaim. Wait for the writeback to complete.
@@ -1190,30 +1190,16 @@ retry:
if (folio_test_writeback(folio)) {
/* Case 1 above */
if (current_is_kswapd() &&
- folio_test_reclaim(folio) &&
+ folio_test_dropbehind(folio) &&
test_bit(PGDAT_WRITEBACK, &pgdat->flags)) {
stat->nr_immediate += nr_pages;
goto activate_locked;
/* Case 2 above */
} else if (writeback_throttling_sane(sc) ||
- !folio_test_reclaim(folio) ||
+ !folio_test_dropbehind(folio) ||
!may_enter_fs(folio, sc->gfp_mask)) {
- /*
- * This is slightly racy -
- * folio_end_writeback() might have
- * just cleared the reclaim flag, then
- * setting the reclaim flag here ends up
- * interpreted as the readahead flag - but
- * that does not matter enough to care.
- * What we do want is for this folio to
- * have the reclaim flag set next time
- * memcg reclaim reaches the tests above,
- * so it will then wait for writeback to
- * avoid OOM; and it's also appropriate
- * in global reclaim.
- */
- folio_set_reclaim(folio);
+ folio_set_dropbehind(folio);
stat->nr_writeback += nr_pages;
goto activate_locked;
@@ -1368,7 +1354,7 @@ retry:
*/
if (folio_is_file_lru(folio) &&
(!current_is_kswapd() ||
- !folio_test_reclaim(folio) ||
+ !folio_test_dropbehind(folio) ||
!test_bit(PGDAT_DIRTY, &pgdat->flags))) {
/*
* Immediately reclaim when written back.
@@ -1378,7 +1364,7 @@ retry:
*/
node_stat_mod_folio(folio, NR_VMSCAN_IMMEDIATE,
nr_pages);
- folio_set_reclaim(folio);
+ folio_set_dropbehind(folio);
goto activate_locked;
}
_
Patches currently in -mm which might be from kirill.shutemov@xxxxxxxxxxxxxxx are
mm-migrate-transfer-pg_dropbehind-to-the-new-folio.patch
drm-i915-gem-convert-__shmem_writeback-to-folios.patch
drm-i915-gem-use-pg_dropbehind-instead-of-pg_reclaim.patch
mm-zswap-use-pg_dropbehind-instead-of-pg_reclaim.patch
mm-truncate-use-folio_set_dropbehind-instead-of-deactivate_file_folio.patch
mm-vmscan-use-pg_dropbehind-instead-of-pg_reclaim.patch
mm-vmscan-use-pg_dropbehind-instead-of-pg_reclaim-in-shrink_folio_list.patch
mm-mglru-check-pg_dropbehind-instead-of-pg_reclaim-in-lru_gen_folio_seq.patch
mm-remove-pg_reclaim.patch
mm-vmscan-do-not-demote-pg_dropbehind-folios.patch
mm-rename-pg_dropbehind-to-pg_reclaim.patch
