Re: Performance of ext4

[Jan Kara <jack@suse.cz>]

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().
> > > 
> > > 
> > 
> > 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 ? 
> 
> or update write_cache_pages not to call writepage if the page is not
> dirty ?
  But that is already happening :) Look a few lines above your patch into
clear_page_dirty_for_io()...

									Honza

> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> index ded57d5..0a13702 100644
> --- a/mm/page-writeback.c
> +++ b/mm/page-writeback.c
> @@ -929,6 +929,11 @@ int write_cache_pages(struct address_space *mapping,
>  				continue;
>  			}
>  
> +			if (!PageDirty(page)) {
> +				unlock_page(page);
> +				continue;
> +			}
> +
>  			ret = (*writepage)(page, wbc, data);
>  
>  			if (unlikely(ret == AOP_WRITEPAGE_ACTIVATE)) {
-- 
Jan Kara <jack@suse.cz>
SUSE Labs, CR