linux-kernel - Re: [PATCH 2.6.20-rc1 00/10] Kernel memory leak detector 0.13

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Date:	Wed, 27 Dec 2006 13:52:46 +0000
From:	"Catalin Marinas" <catalin.marinas@...il.com>
To:	"Ingo Molnar" <mingo@...e.hu>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2.6.20-rc1 00/10] Kernel memory leak detector 0.13

On 18/12/06, Ingo Molnar <mingo@...e.hu> wrote:
> * Catalin Marinas <catalin.marinas@...il.com> wrote:
> > I could also use a simple allocator based on alloc_pages [...]
> > [...] It could be so simple that it would never need to free any
> > pages, just grow the size as required and reuse the freed memleak
> > objects from a list.
>
> sounds good to me. Please make it a per-CPU pool. We'll have to fix the
> locking too, to be per-CPU - memleak_lock is quite a scalability problem
> right now. (Add a memleak_object->cpu pointer so that freeing can be
> done on any other CPU as well.)

I did some simple statistics about allocations happening on one CPU
and freeing on a different one. On a 4-CPU ARM system (and without IRQ
balancing and without CONFIG_PREEMPT), these seem to happen in about
8-10% of the cases. Do you expect higher figures on other
systems/configurations?

As I mentioned in a different e-mail, a way to remove the global hash
table is to create per-cpu hashes. The only problem is that in these
8-10% of the cases, freeing would need to look up the other hashes.
This would become a problem with a high number of CPUs but I'm not
sure whether it would overtake the performance issues introduced by
cacheline ping-ponging in the single-hash case.

Any thoughts?

Thanks.

-- 
Catalin
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