linux-ext4 - Re: [PATCH] jbd jbd2: fix dio writereturningEIOwhentry_to_release

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Message-Id: <6.0.0.20.2.20080811123405.03ec03d0@172.19.0.2>
Date:	Mon, 11 Aug 2008 15:25:54 +0900
From:	Hisashi Hifumi <hifumi.hisashi@....ntt.co.jp>
To:	Chris Mason <chris.mason@...cle.com>
Cc:	Mingming Cao <cmm@...ibm.com>, Jan Kara <jack@...e.cz>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] jbd jbd2: fix dio
  writereturningEIOwhentry_to_release_page fails


>> >> >I am wondering why we need stronger invalidate hurantees for DIO->
>> >> >invalidate_inode_pages_range(),which force the page being removed from
>> >> >page cache? In case of bh is busy due to ext3 writeout,
>> >> >journal_try_to_free_buffers() could return different error number(EBUSY)
>> >> >to try_to_releasepage() (instead of EIO).  In that case,  could we just
>> >> >leave the page in the cache, clean pageuptodate() (to force later buffer
>> >> >read to read from disk) and then invalidate_complete_page2() return
>> >> >successfully? Any issue with this way?
>> >> 
>> >> My idea is that journal_try_to_free_buffers returns EBUSY if it fails due to
>> >> bh busy, and dio write falls back to buffered write. This is easy to fix.
>> >> 
>> >> 
>> >
>> >What about the invalidates done after the DIO has already run
>> >non-buffered?
>> 
>> Dio write falls back to buffered IO when writing to a hole on ext3, I 
>think. I want to 
>> apply this mechanism to fix this issue. When try_to_release_page fails on 
>a page 
>> due to bh busy, dio write does buffered write, sync_page_range, and 
>> wait_on_page_writeback, imvalidates page cache to preserve dio semantics. 
>> Even if page invalidation that is carried out after 
>wait_on_page_writeback fails, 
>> there is no inconsistency between HDD and page cache.
>> 
>
>Sorry, I'm sure I wasn't very clear, I was referencing this code from
>mm/filemap.c:
>
>        written = mapping->a_ops->direct_IO(WRITE, iocb, iov, pos, *nr_segs);
>
>        /*
>         * Finally, try again to invalidate clean pages which might have been
>         * cached by non-direct readahead, or faulted in by get_user_pages()
>         * if the source of the write was an mmap'ed region of the file
>         * we're writing.  Either one is a pretty crazy thing to do,
>         * so we don't support it 100%.  If this invalidation
>         * fails, tough, the write still worked...
>         */
>        if (mapping->nrpages) {
>                invalidate_inode_pages2_range(mapping,
>                                              pos >> PAGE_CACHE_SHIFT, end);
>        }
>
>If this second invalidate fails during a DIO write, we'll have up to
>date pages in cache that don't match the data on disk.  It is unlikely
>to fail because the conditions that make jbd unable to free a buffer are
>rare, but it can still happen with the write combination of mmap usage.
>
>The good news is the second invalidate doesn't make O_DIRECT return
>-EIO.  But, it sounds like fixing do_launder_page to always call into
>the FS can fix all of these problems.  Am I missing something?
>

My approach is not implementing do_launder_page for ext3.
It is needed to modify VFS.

My patch is as follows:
Comments?


diff -Nrup linux-2.6.27-rc2.org/mm/filemap.c linux-2.6.27-rc2/mm/filemap.c
--- linux-2.6.27-rc2.org/mm/filemap.c	2008-08-11 14:33:23.000000000 +0900
+++ linux-2.6.27-rc2/mm/filemap.c	2008-08-11 14:57:29.000000000 +0900
@@ -2129,13 +2129,16 @@ 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().
+	 * -EBUSY without clobbering -EIOCBQUEUED from ->direct_IO().
 	 */
 	if (mapping->nrpages) {
 		written = invalidate_inode_pages2_range(mapping,
 					pos >> PAGE_CACHE_SHIFT, end);
-		if (written)
+		if (written) {
+			if (written == -EBUSY)
+				written = 0;
 			goto out;
+		}
 	}
 
 	written = mapping->a_ops->direct_IO(WRITE, iocb, iov, pos, *nr_segs);
diff -Nrup linux-2.6.27-rc2.org/mm/truncate.c linux-2.6.27-rc2/mm/truncate.c
--- linux-2.6.27-rc2.org/mm/truncate.c	2008-08-11 14:33:24.000000000 +0900
+++ linux-2.6.27-rc2/mm/truncate.c	2008-08-11 14:52:03.000000000 +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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