linux-kernel - Re: block: use kmalloc alignment for bio slab

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Message-ID: <5342EB8A.5060607@fb.com>
Date:	Mon, 7 Apr 2014 12:16:42 -0600
From:	Jens Axboe <axboe@...com>
To:	Mike Snitzer <snitzer@...hat.com>
CC:	<dm-devel@...hat.com>, <mpatocka@...hat.com>,
	<linux-kernel@...r.kernel.org>
Subject: Re: block: use kmalloc alignment for bio slab

On 04/07/2014 12:15 PM, Mike Snitzer wrote:
> On Wed, Apr 02 2014 at  2:04pm -0400,
> Mike Snitzer <snitzer@...hat.com> wrote:
>
>> From: Mikulas Patocka <mpatocka@...hat.com>
>>
>> Various subsystems can ask the bio subsystem to create a bio slab cache
>> with some free space before the bio.  This free space can be used for any
>> purpose.  Device mapper uses this per-bio-data feature to place some
>> target-specific and device-mapper specific data before the bio, so that
>> the target-specific data doesn't have to be allocated separately.
>>
>> This per-bio-data mechanism is used in place of kmalloc, so we need the
>> allocated slab to have the same memory alignment as memory allocated
>> with kmalloc.
>>
>> Change bio_find_or_create_slab() so that it uses ARCH_KMALLOC_MINALIGN
>> alignment when creating the slab cache.  This is needed so that dm-crypt
>> can use per-bio-data for encryption - the crypto subsystem assumes this
>> data will have the same alignment as kmalloc'ed memory.
>>
>> Signed-off-by: Mikulas Patocka <mpatocka@...hat.com>
>> Signed-off-by: Mike Snitzer <snitzer@...hat.com>
>
> Hey Jens,
>
> Just wanted to give you a heads up that I staged this patch in
> linux-dm.git's 'for-next', here:
> https://urldefense.proofpoint.com/v1/url?u=https://git.kernel.org/cgit/linux/kernel/git/device-mapper/linux-dm.git/commit/?h%3Dfor-next%26id%3Dcd433c25f43eb054f62b7b48f1d0349f65b1740c&k=ZVNjlDMF0FElm4dQtryO4A%3D%3D%0A&r=3JMVyziIyZtZ5cv9eWNLwQ%3D%3D%0A&m=yu%2BvHiMLQp0QZVW7KCcxC6XDci1OzHP9ymRaDDIROdk%3D%0A&s=7ac8f47451490f80d8bacbef2487bfa43c0d7c9a1c968558010f06f92e20caca
>
> I rebased it to add this yesterday:
> Acked-by: Jens Axboe <axboe@...com> # via private exchange on facebook
>
> I put this in place because there is a chance I'll still be sending the
> improved dm-crypt parallelization patches to Linus for 3.15 this week.
> So having this go through linux-dm.git saves the awkward coordination
> where otherwise DM would be depending on the block tree.
>
> You OK with this?

Yeah, that's fine.

-- 
Jens Axboe

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