linux-kernel - [PATCH v2 2/2] mm/readahead: don't decrease mmap

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Date: Fri, 22 Mar 2024 17:35:55 +0800
From: Liu Shixin <liushixin2@...wei.com>
To: Jan Kara <jack@...e.cz>, Matthew Wilcox <willy@...radead.org>, Andrew
 Morton <akpm@...ux-foundation.org>, Alexander Viro <viro@...iv.linux.org.uk>,
	Christian Brauner <brauner@...nel.org>
CC: <linux-fsdevel@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<linux-mm@...ck.org>, Liu Shixin <liushixin2@...wei.com>
Subject: [PATCH v2 2/2] mm/readahead: don't decrease mmap_miss when folio has workingset flags

If there are too many folios that are recently evicted in a file, then
they will probably continue to be evicted. In such situation, there is
no positive effect to read-ahead this file since it is only a waste of IO.

The mmap_miss is increased in do_sync_mmap_readahead() and decreased in
both do_async_mmap_readahead() and filemap_map_pages(). In order to skip
read-ahead in above scenario, the mmap_miss have to increased exceed
MMAP_LOTSAMISS. This can be done by stop decreased mmap_miss when folio
has workingset flags. The async path is not to care because in above
scenario, it's hard to run into the async path.

Signed-off-by: Liu Shixin <liushixin2@...wei.com>
---
 mm/filemap.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index 8df4797c5287..753771310127 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -3439,7 +3439,8 @@ static vm_fault_t filemap_map_folio_range(struct vm_fault *vmf,
 		if (PageHWPoison(page + count))
 			goto skip;

-		(*mmap_miss)++;
+		if (!folio_test_workingset(folio))
+			(*mmap_miss)++;

 		/*
 		 * NOTE: If there're PTE markers, we'll leave them to be
@@ -3488,7 +3489,8 @@ static vm_fault_t filemap_map_order0_folio(struct vm_fault *vmf,
 	if (PageHWPoison(page))
 		return ret;

-	(*mmap_miss)++;
+	if (!folio_test_workingset(folio))
+		(*mmap_miss)++;

 	/*
 	 * NOTE: If there're PTE markers, we'll leave them to be
-- 
2.25.1