linux-kernel - Re: [PATCH 4/7] zram/xvmalloc: free bit block insertion optimization

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Message-ID: <AANLkTinMwGf2zDE8MEDCFZtUcVKRYLVZVhzzcdj3TYZf@mail.gmail.com>
Date:	Wed, 26 Jan 2011 20:51:05 +0200
From:	Pekka Enberg <penberg@...nel.org>
To:	Pekka Enberg <penberg@...nel.org>, Nitin Gupta <ngupta@...are.org>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Pekka Enberg <penberg@...helsinki.fi>,
	devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org
Cc:	Robert Jennings <rcj@...ux.vnet.ibm.com>
Subject: Re: [PATCH 4/7] zram/xvmalloc: free bit block insertion optimization

On Wed, Jan 26, 2011 at 8:40 PM, Robert Jennings <rcj@...ux.vnet.ibm.com> wrote:
> * Pekka Enberg (penberg@...nel.org) wrote:
>> On Wed, Jan 26, 2011 at 7:25 PM, Robert Jennings <rcj@...ux.vnet.ibm.com> wrote:
>> > There is no need to set the bits in the first- and second-level indices
>> > to indicate a free page when we know that a free page existed at this
>> > level.
>> >
>> > Signed-off-by: Robert Jennings <rcj@...ux.vnet.ibm.com>
>>
>> Why is it not necessary? I don't know that part of the code well
>> enough to tell if this patch is safe or not.
>
> This change is in a conditional block which is entered only when there is
> an existing data block on the freelist where the insert has taken place.
>
> The new block is pushed onto the freelist stack and this conditional block
> is updating links in the prior stack head to point to the new stack head.
> After this conditional block the first-/second-level indices are updated
> to indicate that there is a free block at this location.
>
> This patch adds an immediate return from the conditional block to avoid
> setting bits again to indicate a free block on this freelist. They would
> already be set because there was an existing free block on this freelist.

Some of that information could be put in the changelog.

Reviewed-by: Pekka Enberg <penberg@...nel.org>
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