Re: Performance of ext4

Aneesh Kumar K.V
2008-06-27T17:36:23Z

On Fri, Jun 27, 2008 at 12:00:24PM +0200, Jan Kara wrote:
> On Fri 27-06-08 15:19:13, Aneesh Kumar K.V wrote:
> > On Fri, Jun 27, 2008 at 02:44:59PM +0530, Aneesh Kumar K.V wrote:
> > > 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().
> > > >
> > > >
> > >

How about this ?

commit 174d555d8effb480a23d5dea8db698d1bc2cfa7d
Author: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Date: Fri Jun 27 23:04:28 2008 +0530

ext4: call ext4_page_mkwrite even for MappedToDisk pages

We can have pages that are fully mapped to disk. The
mappedtodisk flag is used to indicate that every
buffer_head in the page have a mapping block allocated
on disk. But that doesn't gurantee that we have initialized
those buffer_head and added it to page via page->private.
This causes writepage to go BUGON when it find a page
that have NULL page->private.

The fix is to make sure we initialize the buffer_head and add
it to page when we are going to write to the page. This can
be done via ext4_page_mkwrite

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 10f1d5d..11ebe88 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3978,8 +3978,6 @@ int ext4_page_mkwrite(struct vm_area_struct *vma, struct page *page)
goto out_unlock;
}
ret = 0;
- if (PageMappedToDisk(page))
- goto out_unlock;

if (page->index == size >> PAGE_CACHE_SHIFT)
len = size & ~PAGE_CACHE_MASK;