linux-kernel - Re: Patch workqueue: create new slab cache instead of hacking

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Message-ID: <1332341381.7893.17.camel@edumazet-glaptop>
Date:	Wed, 21 Mar 2012 07:49:41 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Tejun Heo <tj@...nel.org>, Lai Jiangshan <laijs@...fujitsu.com>,
	Pekka Enberg <penberg@...nel.org>,
	Matt Mackall <mpm@...enic.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: Patch workqueue: create new slab cache instead of hacking

On Wed, 2012-03-21 at 09:12 -0500, Christoph Lameter wrote:
> How about this instead?
> 
> Subject: workqueues: Use new kmem cache to get aligned memory for workqueues
> 
> The workqueue logic currently improvises by doing a kmalloc allocation and
> then aligning the object. Create a slab cache for that purpose with the
> proper alignment instead.
> 
> Cleans up the code and makes things much simpler. No need anymore to carry
> an additional pointer to the beginning of the kmalloc object.
> 
> Signed-off-by: Christoph Lameter <cl@...ux.com>

Creating a dedicated cache for few objects ? Thats a lot of overhead, at
least for SLAB (no merges of caches)

By the way network stack also wants to align struct net_device (in
function alloc_netdev_mqs(), and uses a custom code.

In this case, as the size of net_device is not constant, we use standard
kzalloc().

No idea why NETDEV_ALIGN is 32 ... Oh well, some old constant instead of
L1_CACHE_BYTES ...





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