linux-kernel - Re: [patch 2/2] slub: add Documentation/ABI/testing/sysfs-kernel-slab

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Message-ID: <alpine.DEB.2.00.0904231549130.32736@chino.kir.corp.google.com>
Date:	Thu, 23 Apr 2009 15:52:36 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Christoph Lameter <cl@...ux.com>
cc:	Pekka Enberg <penberg@...helsinki.fi>,
	Randy Dunlap <randy.dunlap@...cle.com>,
	Nick Piggin <npiggin@...e.de>, linux-kernel@...r.kernel.org
Subject: Re: [patch 2/2] slub: add
 Documentation/ABI/testing/sysfs-kernel-slab

On Thu, 23 Apr 2009, Christoph Lameter wrote:

> >  - slqb uses /sys/kernel/slab as well and we simply add its files in
> >    sysfs-kernel-slab and leave it to userspace to test for which allocator
> >    is actually being used.  Both allocators share many of the same
> >    fundamental attributes but some are only applicable to one,
> >
> >  - slqb moves to /sys/kernel/slqb since slub is already resident in
> >    /sys/kernel/slab and the mm/slab.c allocator actually has no sysfs
> >    interface, or
> 
> slqb cannot be concurrently used with slub. So slqb can use
> /sys/kernel/slab as well. So could the original slab allocator.
> Dont change this.
> 

I'm more concerned with the userspace API.  You're comfortable with 
letting userspace determine what allocator the kernel is using either by 
testing for the presence of certain slub or slqb-specific files or 
checking the config?

That should be fine since there's parity among the files that both 
allocators share, but seems fragile if an allocator adds a file that was 
previously only applicable to the other or the API happens to change.

My thinking was that /sys/kernel/slqb would be a permanent reference point 
that userspace could easily test to determine what API is available.
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