[<prev] [next>] [<thread-prev] [day] [month] [year] [list]
Date: Sun, 23 Nov 2008 20:02:58 +0530
From: "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To: Mingming Cao <cmm@...ibm.com>
Cc: "Theodore Ts'o" <tytso@....edu>,
Ext4 Developers List <linux-ext4@...r.kernel.org>,
Aneesh Kumar <aneesh.kumar@...il.com>
Subject: Re: [PATCH] ext4: calculate journal credits correctly
On Wed, Nov 12, 2008 at 04:03:42PM -0800, Mingming Cao wrote:
>
> 在 2008-11-06四的 14:51 -0500,Theodore Ts'o写道:
> > This fixes a 2.6.27 regression which was introduced in commit a02908f1.
> >
> > We weren't passing the chunk parameter down to the two subections,
> > ext4_indirect_trans_blocks() and ext4_ext_index_trans_blocks(), with
> > the result that massively overestimate the amount of credits needed by
> > ext4_da_writepages, especially in the non-extents case. This causes
> > failures especially on /boot partitions, which tend to be small and
> > non-extent using since GRUB doesn't handle extents.
> >
> > Thanks to Joseph Fannin for reporting this bug.
> >
> Thanks for fixing this up!
This was sent to my gmail.com id so missed it before.
>
> However, looking at the code path, I wasn't sure if we got the delalloc
> credits right. In ext4_da_writepages()->mpage_da_writepages(), the
> credits is calculated based on the assumption that mpage_da_writepages()
> doing* one* single chunk of contigugous allocation? So only one single
> extent credit is reserved (here you see the "chunk" flag passed from the
> ext4_da_writepages)
>
> __mpage_da_writepage() does do single chunk of block allocation at a
> time, but mpage_da_writepages()->write_cache_pages() will loop the page
> vectors and probably will calling writepage->__mpage_da_writepage->
> mpage_da_map_blocks() multiple times? Am I missing anything?
>
mpage_da_writepages does block allocation for single chunk only.
ext4_da_writepages allocate credit needed for single chunk allocation.
write_cache_pages iterate through contiguous pages and build an in
memory extent. It then call get_blocks for 'x' blocks. After that
we map the blocks to the unmapped buffer_heads. Then we do
ext4_da_writepage which redirty pages which are not fully mapped. That
means we skip pages. We retry using mpage_data_writepages again.
-aneesh
--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Powered by blists - more mailing lists