[045/178] mm/filemap: drop check for truncated page after I/O

Commit Message

Andrew Morton April 30, 2021, 5:55 a.m. UTC

From: "Matthew Wilcox (Oracle)" <[e-mail]>
Subject: 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.

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Matthew Wilcox (Oracle) <[e-mail]>
Acked-by: William Kucharski <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

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

Patch

--- a/mm/filemap.c~mm-filemap-drop-check-for-truncated-page-after-i-o
+++ a/mm/filemap.c
@@ -2348,8 +2348,6 @@  static int filemap_read_page(struct file
 		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;
 }