linux-kernel - [PATCH] mm/filemap: Drop check for truncated page after I/O

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Message-Id: <20210303222547.1056428-1-willy@infradead.org>
Date:   Wed,  3 Mar 2021 22:25:47 +0000
From:   "Matthew Wilcox (Oracle)" <willy@...radead.org>
To:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Miklos Szeredi <mszeredi@...hat.com>
Cc:     "Matthew Wilcox (Oracle)" <willy@...radead.org>
Subject: [PATCH] mm/filemap: Drop check for truncated page after I/O

If the I/O completed successfully, the page will remain Uptodate,
even if it is subsequently truncated.  If the I/O completed with an error,
this check would cause us to retry the I/O if the page were truncated
before we woke up.  There is no need to retry the I/O; the I/O to fill
the page failed, so we can legitimately just return -EIO.

This code was originally added by commit 56f0d5fe6851 ("[PATCH]
readpage-vs-invalidate fix") in 2005 (this commit ID is from the
linux-fullhistory tree; it is also commit ba1f08f14b52 in tglx-history).

At the time, truncate_complete_page() called ClearPageUptodate(), and
so this was fixing a real bug.  In 2008, commit 84209e02de48
("mm: dont clear PG_uptodate on truncate/invalidate") removed the
call to ClearPageUptodate, and this check has been unnecessary ever
since.

It doesn't do any real harm, but there's no need to keep it.

Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
---
 mm/filemap.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index 8d3e0daed7c9..3d1635d3be3e 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2238,8 +2238,6 @@ static int filemap_read_page(struct file *file, struct address_space *mapping,
 		return error;
 	if (PageUptodate(page))
 		return 0;
-	if (!page->mapping)	/* page truncated */
-		return AOP_TRUNCATED_PAGE;
 	shrink_readahead_size_eio(&file->f_ra);
 	return -EIO;
 }
-- 
2.30.0