linux-ext4 - Re: [PATCH V2] ext4: speed-up releasing blocks on commit

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Date:	Fri, 21 Sep 2012 00:43:49 -0400
From:	Andrey Sidorov <qrxd43@...orola.com>
To:	linux-ext4@...r.kernel.org
Subject: Re: [PATCH V2] ext4: speed-up releasing blocks on commit

On Fri, Sep 21, 2012 at 12:11 AM, Andrey Sidorov <qrxd43@...orola.com>
wrote:
>
> Improve mb_free_blocks speed by clearing bits all at once instead of going
> one by one.
> Rebuild buddy bitmap by going up only once per range instead of once per
> block.
> For example, for 60G file commit callback time drops from 2.7s to 5ms.
> This is especially good for non-preemptive kernels as there is no
> rescheduling during release.

I realised that current implementation garbles bb_free, bb_counters
and bb_fragments upon double free. I think simplest and the only
reliable way to recover is rebuild buddy off bitmap and that's what I
did.
Tested it with AGGRESSIVE_CHECK defined and mb_check_buddy running at
each invocation. I've also injected bit flips into mb_free_blocks to
ensure regeneration is successful.
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