linux-ext4 - Re: [PATCH] ext4: invalidate gap cache when writing extents last block

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Message-ID: <4DDCC4EB.5000007@sx.jp.nec.com>
Date:	Wed, 25 May 2011 17:59:23 +0900
From:	Kazuya Mio <k-mio@...jp.nec.com>
To:	Lukas Czerner <lczerner@...hat.com>
CC:	linux-ext4@...r.kernel.org, tytso@....edu
Subject: Re: [PATCH] ext4: invalidate gap cache when writing extents last
 block

2011/05/24 17:57, Lukas Czerner wrote:
> Hi Kazuya,
>
> I am really sorry for late answer. I think you're partly right. my
> solution is not good, but I still think that your is not good as well. I
> need to look at this again and more closely, sorry.
>
> What do you think about this: ext4_ext_next_allocated_block() should
> return next allocated block, however instead it in some cases returns
> EXT_MAX_BLOCK, which points at the last logical block in a file, which
> however in some cases might be equal to the last not allocated block,
> not first allocated block in subsequent extent. And boom, we have (next
> == lblock).

I think so, too.

> So if we want to really return next allocated block (or more
> specifically, next block which we can not allocate), we should in those
> cases return EXT_MAX_BLOCK+1. And we should do this in
> ext4_ext_put_gap_in_cache() as well when there is no extent yet. Also
> note that as I said EXT_MAX_BLOCK means maximum logical block, however
> we use it as lenght in ext4_ext_put_gap_in_cache() which does not sound
> right either. It seems all a little bit messy :-/. I need to look at it
> and try it to see if it would work, but I think it does make sense.
>
> What do you think?

AFAIK, it's the best way to fix this problem. But I have no idea that doesn't
increase the size of struct ext4_ext_cache. I'm looking forward to seeing
the patch.

Regards,
Kazuya Mio
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