Re: [PATCH 1/1] network memory allocator.

From: Evgeniy Polyakov
Date: Mon Aug 14 2006 - 07:44:08 EST

On Mon, Aug 14, 2006 at 01:40:21PM +0200, Andi Kleen (ak@xxxxxxx) wrote:
> Evgeniy Polyakov <johnpol@xxxxxxxxxxx> writes:
> > Design notes.
> > Original idea was to store meta information used for allocation in an
> > AVL tree [1], but since I found a way to use some "unused" fields in struct page,
> > tree is unused in the allocator.
> But there seems to be still an AVL tree in there?

Tree structure can be used for simpler memory addon/removal from
hotplug, but I have not that in mind.
It will be removed soon.

> > Benchmarks with trivial epoll based web server showed noticeble (more
> > than 40%) imrovements of the request rates (1600-1800 requests per
> > second vs. more than 2300 ones). It can be described by more
> > cache-friendly freeing algorithm, by tighter objects packing and thus
> > reduced cache line ping-pongs, reduced lookups into higher-layer caches
> > and so on.
> So what are its drawbacks compared to slab/kmalloc?

Hmm... Bigger per-page overhead (additional bitmask of free/used
objects). More complex algorithm behind freeing.

> Also if it really performs that much better it might be a good
> idea to replace all of kmalloc() with it, but doing that
> would require a lot more benchmarks with various workloads
> and small and big machines first.

First user can be MMU-less systems which suffer noticebly from
fragmentations and power-of-two overhead.

> -Andi

Evgeniy Polyakov
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