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

[Andrew Morton <akpm@linux-foundation.org>]

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

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------------------------------------------------------
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