FAILED: patch "[PATCH] madvise:madvise_free_pte_range(): don't use mapcount()" failed to apply to 6.4-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 6.4-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.4.y
git checkout FETCH_HEAD
git cherry-pick -x 0e0e9bd5f7b9d40fd03b70092367247d52da1db0
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2023082614-choice-mongoose-0731@gregkh' --subject-prefix 'PATCH 6.4.y' HEAD^..

Possible dependencies:



thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 0e0e9bd5f7b9d40fd03b70092367247d52da1db0 Mon Sep 17 00:00:00 2001
From: Yin Fengwei <fengwei.yin@intel.com>
Date: Tue, 8 Aug 2023 10:09:17 +0800
Subject: [PATCH] madvise:madvise_free_pte_range(): don't use mapcount()
 against large folio for sharing check

Commit 98b211d6415f ("madvise: convert madvise_free_pte_range() to use a
folio") replaced the page_mapcount() with folio_mapcount() to check
whether the folio is shared by other mapping.

It's not correct for large folios. folio_mapcount() returns the total
mapcount of large folio which is not suitable to detect whether the folio
is shared.

Use folio_estimated_sharers() which returns a estimated number of shares.
That means it's not 100% correct. It should be OK for madvise case here.

User-visible effects is that the THP is skipped when user call madvise.
But the correct behavior is THP should be split and processed then.

NOTE: this change is a temporary fix to reduce the user-visible effects
before the long term fix from David is ready.

Link: https://lkml.kernel.org/r/20230808020917.2230692-4-fengwei.yin@intel.com
Fixes: 98b211d6415f ("madvise: convert madvise_free_pte_range() to use a folio")
Signed-off-by: Yin Fengwei <fengwei.yin@intel.com>
Reviewed-by: Yu Zhao <yuzhao@google.com>
Reviewed-by: Ryan Roberts <ryan.roberts@arm.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Vishal Moola (Oracle) <vishal.moola@gmail.com>
Cc: Yang Shi <shy828301@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/madvise.c b/mm/madvise.c
index 46802b4cf65a..ec30f48f8f2e 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -680,7 +680,7 @@ static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr,
 		if (folio_test_large(folio)) {
 			int err;
 
-			if (folio_mapcount(folio) != 1)
+			if (folio_estimated_sharers(folio) != 1)
 				break;
 			if (!folio_trylock(folio))
 				break;