linux-kernel - Re: SLUB 0:1 SLAB (OOM during massive parallel kernel builds)

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Date:	Tue, 23 Oct 2007 13:09:31 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	Pekka Enberg <penberg@...helsinki.fi>
cc:	Alexey Dobriyan <adobriyan@...il.com>,
	linux-kernel@...r.kernel.org, linux-mm@...r.kernel.org
Subject: Re: SLUB 0:1 SLAB (OOM during massive parallel kernel builds)

On Tue, 23 Oct 2007, Pekka Enberg wrote:

> On 10/23/07, Christoph Lameter <clameter@....com> wrote:
> > Not sure what this is. Maybe the slowing SLUB solves the race.
> 
> What kind of race are you thinking of? What I initially thought was
> that the problem is that SLUB messes up some other VM heuristics due
> to different object sizes, not holding on to empty slabs, and/or page
> allocator pass-through. I guess only object size is affected by
> debugging, though?

The number of objects per page is reduced by enabling full debugging. That 
triggers a potential of more order 1 allocations but we are failing at 
order 0 allocs. slub_debug=F does not increase object size with debugging 
information but keeps things as they are while doing as much verification 
of slab integrity as possible.

One--potentially far fetched theory--is that the difference in alloc 
performance may trigger a race. But I guess it is more likely that we will 
find something wrong with the gfp flags (that I recategorized for 2.6.24).

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