linux-ext4 - Re: [PATCH] ext4: Do not zeroout uninitialized extents beyond i

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Message-ID: <871ve0qb59.fsf@openvz.org>
Date:	Wed, 28 Apr 2010 11:38:58 +0400
From:	Dmitry Monakhov <dmonakhov@...nvz.org>
To:	"Aneesh Kumar K. V" <aneesh.kumar@...ux.vnet.ibm.com>
Cc:	linux-ext4@...r.kernel.org, tytso@....edu
Subject: Re: [PATCH] ext4: Do not zeroout uninitialized extents beyond i_size

"Aneesh Kumar K. V" <aneesh.kumar@...ux.vnet.ibm.com> writes:

> On Fri,  9 Apr 2010 21:22:28 +0400, Dmitry Monakhov <dmonakhov@...nvz.org> wrote:
>> Zerrout trick allow us to optimize cases where it is more reasonable
>> to explicitly zeroout extent and mark it as initialized instead of
>> splitting to several small ones.
>> But this optimization is not acceptable is extent is beyond i_size
>> Because it is not possible to have initialized blocks after i_size.
>> Fsck treat this as incorrect inode size.
>> 
>
> With commit c8d46e41bc744c8fa0092112af3942fcd46c8b18 if we set
> EXT4_EOFBLOCKS_FL we should be able to have blocks beyond i_size.
> May be the zero out path should set the flag instead of doing all these
> changes. Zero-out is already complex with all the ENOSPC related
> consideration. I guess we should try to keep it simple.
For initialized extent beyond i_size? I've check fsck and seems that
is truly possible. So this optimization allow us to avoid some 
bad EIO situations. But we have to rework ext_get_blocks( ,create == 1)
to clear EXT4_EOFBLOCKS_FL if last block of latest_extent is requested.
I'll handle this.
>
> -aneesh
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