Re: [PATCH 0/3] Ext3 latency improvement patches

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On Fri, Mar 27, 2009 at 05:30:52PM -0400, Theodore Tso wrote:
> On Fri, Mar 27, 2009 at 05:03:38PM -0400, Chris Mason wrote:
> > > Ric had asked me about a test program that would show the worst case
> > > ext3 behavior.  So I've modified your ext3 program a little.  It now
> > > creates a 8G file and forks off another proc to do random IO to that
> > > file.
> > > 
> > 
> > My understanding of ext4 delalloc is that once blocks are allocated to
> > file, we go back to data=ordered.  
> 
> Yes, that's correct.
> 
> > Ext4 is going pretty slowly for this fsync test (slower than ext3), it
> > looks like we're going for a very long time in
> > jbd2_journal_commit_transaction -> write_cache_pages.
> 
> One of the things that we can do to optimize this case for ext4 (and
> ext3) is that if block has already been written out to disk once, we
> don't have to flush it to disk a second time.  So if we add a new
> buffer_head flag which can distinguish between blocks that have been
> newly allocated (and not yet been flushed to disk) versus blocks that
> have already been flushed to disk at least once, we wouldn't need to
> force I/O for blocks in the latter case.

write_cache_pages should only look at pages which are marked dirty right
?. So why are we writing these pages again and again ?

-aneesh
--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html

[Index of Archives]     [Reiser Filesystem Development]     [Ceph FS]     [Kernel Newbies]     [Security]     [Netfilter]     [Bugtraq]     [Linux FS]     [Yosemite National Park]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Linux RAID]     [Samba]     [Device Mapper]     [Linux Media]

  Powered by Linux