Re: [PATCH] SLUB: revert direct page allocator pass through

From: Nick Piggin
Date: Fri Jan 23 2009 - 10:13:32 EST

On Saturday 24 January 2009 02:03:22 Christoph Lameter wrote:
> On Fri, 23 Jan 2009, Nick Piggin wrote:
> > Hmm, it lists quite a number of advantages that I guess are being
> > reverted too? What was the test case(s) that prompted this commit
> > in the first place? Better ensure it doesn't slow down...
> The advantage was mainly memory savings and abilty to redefined kmallocs
> to go directly to the page allocator. Totally avoids slab allocator
> overhead.

Well it sounds in the changelog like a massive performance advantage.
Unfortunately it doesn't really say what the workload was.

> I thought higher order allocations were not supposed to be used in
> performance critical paths?

? You use them all the time in SLUB alone.

> Didnt you want to do everything with order-0
> allocs?

People don't always do what I think is best, unfortunately ;)

> It seems that we currently need the slab allocators to compensate for the
> performance problems in the page allocator for these higher order allocs.
> I'd rather have the page allocator fixed but things are as they are.

No objections from me with speeding up the page allocator of course.

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