linux-ext4 - Re: delalloc and reservation.

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Date:	Mon, 29 Oct 2007 20:03:23 +0530
From:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:	Alex Tomas <bzzz.tomas@...il.com>
CC:	Andreas Dilger <adilger@...sterfs.com>,
	Eric Sandeen <sandeen@...hat.com>,
	Valerie Clement <valerie.clement@...l.net>,
	Theodore Tso <tytso@....edu>, Mingming Cao <cmm@...ibm.com>,
	linux-ext4 <linux-ext4@...r.kernel.org>
Subject: Re: delalloc and reservation.



Alex Tomas wrote:
> Hi,
> 
> could you try the patch attached. it should fix the issue. the idea
> was to align requests in order to help raid5-like setups. but somewhere
> I lost one bit in mballoc: it should pre-allocate all crossed stripes,
> but it didn't.
> 
> as for discard, lustre doesn't use open/close for data, so discard-on-close
> makes zero sense in our case. I'm not very positive whether we need to
> drop preallocation on file close in case of delayed allocation as writeback
> can be started while file is open and finish after close(2).
> 
> 

mballoc by default doesn't give the particular layout only if i force small
size to use inode preallocation i am hitting the problem. ie to change the
below line in ext4_mb_group_or_file

 if (ac->ac_o_ex.fe_len >= sbi->s_mb_small_req)

to 

if (ac->ac_o_ex.fe_len <= sbi->s_mb_small_req)

Do you want to test the patch with this change ?

We are observing the problem with delalloc and nomballoc.


-aneesh
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