Re: Performance of ext4

Aneesh Kumar K.V
2008-06-27T09:24:18Z

On Wed, Jun 25, 2008 at 05:46:39PM -0700, Mingming wrote:
>
> On Wed, 2008-06-25 at 09:09 +0000, Holger Kiehl wrote:
> > On Tue, 24 Jun 2008, Mingming wrote:
> >
> > >
> > > On Tue, 2008-06-24 at 21:12 +0000, Holger Kiehl wrote:
> > >> Yes, with this patch applied on top of latest patch queue I no longer
> > >> get truncated files, after running a short test. Tomorrow I will do some
> > >> more thorough testing and use the patch you have send to me in a separate
> > >> mail. The above patch did not apply but it was easy to apply by hand.
> > >
> > >
> > > Thanks for quick response and test. I have updated the patch queue with
> > > above patch merged. Please let me know if you still see apply issue and
> > > file size update issue with current patch queue.
> > >
> > Thanks, it applies without any problems. However I still hit an oops. What
> > I find strange is that I got the oops just as the benchmark is done and
> > all process where shutting down. The same behaviour I reported here:
> > http://www.ussg.iu.edu/hypermail/linux/kernel/0806.2/2113.html
> > Only this time I got just one oops. This is on x86_64 system (4 Opteron CPU's
> > and SW Raid 1+0). I have not seen this on my home system x86 (1 Dual Core
> > and HW Raid). Anyway, here the dmesg output:
> >
> > kjournald2 starting. Commit interval 15 seconds
> > EXT4 FS on md7, internal journal
> > EXT4-fs: mounted filesystem with ordered data mode.
> > EXT4-fs: file extents enabled
> > EXT4-fs: mballoc enabled
> > JBD: barrier-based sync failed on md7 - disabling barriers
> > ------------[ cut here ]------------
> > kernel BUG at fs/ext4/inode.c:1667!
>
> Did not get a chance to look more closely today, but it's point to this
> code in ext4_da_writepage()
>
> page_bufs = page_buffers(page);
>
> and appearently it's BUG_ON at
> BUG_ON(!PagePrivate(page)); in page_buffers().
>
>

Ok so we are doing the journal_commit and meanwhile shrink_page_list
dropped the buffer. I guess what is happening is

journal_submit_inode_data_buffers
generic_writepages
write_cache_pages
pagevec_lookup_tag(..PAGECACHE_TAG_DIRTY,..)
foreach(page)
shrink_page_list
lock_page
ext4_releasepage
try_to_free_buffers
drop_buffers
cancel_dirty_page
unlock_page
lock_page()
BUG_ON(!PagePrivate(page));

How about the below ? I am not sure journalled mode writepage would need a
simillar change. We don't need to redirty the page because
that would mean the next journal_commit will hit the BUG_ON.
If we need to do a BUG_ON

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index fd67b34..94e5ab0 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -1662,8 +1662,17 @@ static int ext4_da_writepage(struct page *page,
* writing the page in case we would have to do so.
* We reach here also via journal_submit_inode_data_buffers
*/
+ if (!page_has_buffers(page)) {
+ /*
+ * This can happen when we are called via
+ * journal_submit_inode_data_buffers and
+ * shrink_page_list parallely did drop_buffers
+ * after write_cache_pages did a pagevec_lookup_tag
+ */
+ unlock_page(page);
+ return 0;
+ }
size = i_size_read(inode);
-
page_bufs = page_buffers(page);
if (page->index == size >> PAGE_CACHE_SHIFT)
len = size & ~PAGE_CACHE_MASK;
@@ -2046,7 +2055,16 @@ static int ext4_normal_writepage(struct page *page,
loff_t len;

J_ASSERT(PageLocked(page));
- J_ASSERT(page_has_buffers(page));
+ if (!page_has_buffers(page)) {
+ /*
+ * This can happen when we are called via
+ * journal_submit_inode_data_buffers and
+ * shrink_page_list parallely did drop_buffers
+ * after write_cache_pages did a pagevec_lookup_tag
+ */
+ unlock_page(page);
+ return 0;
+ }
if (page->index == size >> PAGE_CACHE_SHIFT)
len = size & ~PAGE_CACHE_MASK;
else