+ mm-swap_state-update-zswap-lrus-protection-range-with-the-folio-locked.patch added to mm-hotfixes-unstable branch

+ mm-swap_state-update-zswap-lrus-protection-range-with-the-folio-locked.patch added to mm-hotfixes-unstable branch

[Andrew Morton]

The patch titled
     Subject: mm/swap_state: update zswap LRU's protection range with the folio locked
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     mm-swap_state-update-zswap-lrus-protection-range-with-the-folio-locked.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-swap_state-update-zswap-lrus-protection-range-with-the-folio-locked.patch

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

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------------------------------------------------------
From: Nhat Pham <nphamcs@gmail.com>
Subject: mm/swap_state: update zswap LRU's protection range with the folio locked
Date: Mon, 5 Feb 2024 15:24:42 -0800

Move the zswap LRU protection range update above the swap_read_folio()
call, and only when a new page is allocated.  This is the case where
(z)swapin could happen, which is a signal that the zswap shrinker should
be more conservative with its reclaiming action.

It also prevents a race, in which folio migration can clear the memcg_data
of the now unlocked folio, resulting in a warning in the inlined
folio_lruvec() call.

Link: https://lkml.kernel.org/r/20240205232442.3240571-1-nphamcs@gmail.com
Fixes: b5ba474f3f51 ("zswap: shrink zswap pool based on memory pressure")
Reported-by: syzbot+17a611d10af7d18a7092@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/all/000000000000ae47f90610803260@google.com/
Signed-off-by: Nhat Pham <nphamcs@gmail.com>
Cc: Chengming Zhou <chengming.zhou@linux.dev>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Yosry Ahmed <yosryahmed@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/swap_state.c |   10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

--- a/mm/swap_state.c~mm-swap_state-update-zswap-lrus-protection-range-with-the-folio-locked
+++ a/mm/swap_state.c
@@ -680,9 +680,10 @@ skip:
 	/* The page was likely read above, so no need for plugging here */
 	folio = __read_swap_cache_async(entry, gfp_mask, mpol, ilx,
 					&page_allocated, false);
-	if (unlikely(page_allocated))
+	if (unlikely(page_allocated)) {
+		zswap_folio_swapin(folio);
 		swap_read_folio(folio, false, NULL);
-	zswap_folio_swapin(folio);
+	}
 	return folio;
 }
 
@@ -855,9 +856,10 @@ skip:
 	/* The folio was likely read above, so no need for plugging here */
 	folio = __read_swap_cache_async(targ_entry, gfp_mask, mpol, targ_ilx,
 					&page_allocated, false);
-	if (unlikely(page_allocated))
+	if (unlikely(page_allocated)) {
+		zswap_folio_swapin(folio);
 		swap_read_folio(folio, false, NULL);
-	zswap_folio_swapin(folio);
+	}
 	return folio;
 }
 
_

Patches currently in -mm which might be from nphamcs@gmail.com are

mm-swap_state-update-zswap-lrus-protection-range-with-the-folio-locked.patch
selftests-zswap-add-zswap-selftest-file-to-zswap-maintainer-entry.patch
selftests-fix-the-zswap-invasive-shrink-test.patch
selftests-add-zswapin-and-no-zswap-tests.patch