+ mm-do-not-start-end-writeback-for-pages-stored-in-zswap.patch added to mm-unstable branch

+ mm-do-not-start-end-writeback-for-pages-stored-in-zswap.patch added to mm-unstable branch

[Andrew Morton]

The patch titled
     Subject: mm: do not start/end writeback for pages stored in zswap
has been added to the -mm mm-unstable branch.  Its filename is
     mm-do-not-start-end-writeback-for-pages-stored-in-zswap.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-do-not-start-end-writeback-for-pages-stored-in-zswap.patch

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

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
      reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days

------------------------------------------------------
From: Usama Arif <usamaarif642@gmail.com>
Subject: mm: do not start/end writeback for pages stored in zswap
Date: Mon, 10 Jun 2024 15:30:37 +0100

start/end writeback combination incorrectly increments NR_WRITTEN counter,
eventhough the pages aren't written to disk.  Pages successfully stored in
zswap should just unlock folio and return from writepage.

Link: https://lkml.kernel.org/r/20240610143037.812955-1-usamaarif642@gmail.com
Signed-off-by: Usama Arif <usamaarif642@gmail.com>
Cc: Chengming Zhou <chengming.zhou@linux.dev>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: kernel-team@meta.com
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Yosry Ahmed <yosryahmed@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/page_io.c |    2 --
 1 file changed, 2 deletions(-)

--- a/mm/page_io.c~mm-do-not-start-end-writeback-for-pages-stored-in-zswap
+++ a/mm/page_io.c
@@ -196,9 +196,7 @@ int swap_writepage(struct page *page, st
 		return ret;
 	}
 	if (zswap_store(folio)) {
-		folio_start_writeback(folio);
 		folio_unlock(folio);
-		folio_end_writeback(folio);
 		return 0;
 	}
 	if (!mem_cgroup_zswap_writeback_enabled(folio_memcg(folio))) {
_

Patches currently in -mm which might be from usamaarif642@gmail.com are

mm-do-not-start-end-writeback-for-pages-stored-in-zswap.patch

+ mm-do-not-start-end-writeback-for-pages-stored-in-zswap.patch added to mm-unstable branch

[Andrew Morton]

The patch titled
     Subject: mm: do not start/end writeback for pages stored in zswap
has been added to the -mm mm-unstable branch.  Its filename is
     mm-do-not-start-end-writeback-for-pages-stored-in-zswap.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-do-not-start-end-writeback-for-pages-stored-in-zswap.patch

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

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
      reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days

------------------------------------------------------
From: Usama Arif <usamaarif642@gmail.com>
Subject: mm: do not start/end writeback for pages stored in zswap
Date: Mon, 10 Jun 2024 15:30:37 +0100

Most of the work done in folio_start_writeback is reversed in
folio_end_writeback.  For e.g.  NR_WRITEBACK and NR_ZONE_WRITE_PENDING are
incremented in start_writeback and decremented in end_writeback.  Calling
end_writeback immediately after start_writeback (separated by
folio_unlock) cancels the affect of most of the work done in start hence
can be removed.

There is some extra work done in folio_end_writeback, however it is
incorrect/not applicable to zswap:
- folio_end_writeback incorrectly increments NR_WRITTEN counter,
  eventhough the pages aren't written to disk, hence this change
  corrects this behaviour.
- folio_end_writeback calls folio_rotate_reclaimable, but that only
  makes sense for async writeback pages, while for zswap pages are
  synchronously reclaimed.

Link: https://lkml.kernel.org/r/20240612100109.1616626-1-usamaarif642@gmail.com
Link: https://lkml.kernel.org/r/20240610143037.812955-1-usamaarif642@gmail.com
Signed-off-by: Usama Arif <usamaarif642@gmail.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Shakeel Butt <shakeel.butt@linux.dev>
Acked-by: Yosry Ahmed <yosryahmed@google.com>
Reviewed-by: Chengming Zhou <chengming.zhou@linux.dev>
Suggested-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Nhat Pham <nphamcs@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/page_io.c |    2 --
 1 file changed, 2 deletions(-)

--- a/mm/page_io.c~mm-do-not-start-end-writeback-for-pages-stored-in-zswap
+++ a/mm/page_io.c
@@ -196,9 +196,7 @@ int swap_writepage(struct page *page, st
 		return ret;
 	}
 	if (zswap_store(folio)) {
-		folio_start_writeback(folio);
 		folio_unlock(folio);
-		folio_end_writeback(folio);
 		return 0;
 	}
 	if (!mem_cgroup_zswap_writeback_enabled(folio_memcg(folio))) {
_

Patches currently in -mm which might be from usamaarif642@gmail.com are

mm-do-not-start-end-writeback-for-pages-stored-in-zswap.patch