linux-ext4 - Re: [PATCH] jbd jbd2: fix diowritereturningEIOwhentry_to_release

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Message-Id: <6.0.0.20.2.20080819113242.03f9e8c8@172.19.0.2>
Date:	Tue, 19 Aug 2008 16:03:45 +0900
From:	Hisashi Hifumi <hifumi.hisashi@....ntt.co.jp>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Chris Mason <chris.mason@...cle.com>, Jan Kara <jack@...e.cz>
Cc:	Mingming Cao <cmm@...ibm.com>, linux-ext4@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, Zach Brown <zach.brown@...cle.com>
Subject: Re: [PATCH] jbd jbd2: fix
  diowritereturningEIOwhentry_to_release_page fails


At 21:59 08/08/13, Chris Mason wrote:
>On Wed, 2008-08-13 at 12:16 +0200, Jan Kara wrote:
>
>> > With that said, I don't have strong feelings against falling back to
>> > buffered IO when the invalidate fails.  Maybe Zach remembers something I
>> > don't?
>>   I don't have a strong opinion either. Falling back to buffered writes is
>> simpler at least for ext3/ext4 because properly synchronizing against
>> writepage() call does not seem to have a nice solution either in
>> do_launder_page() or in releasepage(). OTOH is hides the fact the invalidate
>> is failing and so if we screw up something in future and it fails often, it
>> might be hard to notice / track down the performance penalty.
>
>In general, these races don't happen often, and when they do it is
>because someone is mixing page cache and O_DIRECT io to the same file.
>That is explicitly outside the main use case of O_DIRECT.
>
>So, I'd rather see us slow down O_DIRECT in the mixed use case than have
>big impacts in complexity or speed to other parts of the kernel.  If
>falling back avoids problems in some filesystems or avoids clearing the
>uptodate bit unexpectedly, I'd much rather take the fallback patch.
>
>-chris

Hi Andrew.
I think we don't have strong feelings against falling back to buffered writes to
fix the direct-io -EIO problem.

Please review my patch.

Signed-off-by: Hisashi Hifumi <hifumi.hisashi@....ntt.co.jp>

diff -Nrup linux-2.6.27-rc3.org/mm/filemap.c linux-2.6.27-rc3/mm/filemap.c
--- linux-2.6.27-rc3.org/mm/filemap.c	2008-08-13 13:48:47.000000000 +0900
+++ linux-2.6.27-rc3/mm/filemap.c	2008-08-19 15:45:31.000000000 +0900
@@ -2129,13 +2129,20 @@ generic_file_direct_write(struct kiocb *
 	 * After a write we want buffered reads to be sure to go to disk to get
 	 * the new data.  We invalidate clean cached page from the region we're
 	 * about to write.  We do this *before* the write so that we can return
-	 * -EIO without clobbering -EIOCBQUEUED from ->direct_IO().
+	 * without clobbering -EIOCBQUEUED from ->direct_IO().
 	 */
 	if (mapping->nrpages) {
 		written = invalidate_inode_pages2_range(mapping,
 					pos >> PAGE_CACHE_SHIFT, end);
-		if (written)
+		/*
+		 * If a page can not be invalidated, return 0 to fall back
+		 * to buffered write.
+		 */
+		if (written) {
+			if (written == -EBUSY)
+				return 0;
 			goto out;
+		}
 	}
 
 	written = mapping->a_ops->direct_IO(WRITE, iocb, iov, pos, *nr_segs);
diff -Nrup linux-2.6.27-rc3.org/mm/truncate.c linux-2.6.27-rc3/mm/truncate.c
--- linux-2.6.27-rc3.org/mm/truncate.c	2008-08-13 13:48:48.000000000 +0900
+++ linux-2.6.27-rc3/mm/truncate.c	2008-08-19 12:10:46.000000000 +0900
@@ -380,7 +380,7 @@ static int do_launder_page(struct addres
  * Any pages which are found to be mapped into pagetables are unmapped prior to
  * invalidation.
  *
- * Returns -EIO if any pages could not be invalidated.
+ * Returns -EBUSY if any pages could not be invalidated.
  */
 int invalidate_inode_pages2_range(struct address_space *mapping,
 				  pgoff_t start, pgoff_t end)
@@ -440,7 +440,7 @@ int invalidate_inode_pages2_range(struct
 			ret2 = do_launder_page(mapping, page);
 			if (ret2 == 0) {
 				if (!invalidate_complete_page2(mapping, page))
-					ret2 = -EIO;
+					ret2 = -EBUSY;
 			}
 			if (ret2 < 0)
 				ret = ret2;

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