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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

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>
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/