Re: [Patch 2/3] fast VMA recycling

[Andi Kleen <ak@suse.de>]

On Thursday 23 February 2006 10:48, Arjan van de Ven wrote:
> On Thu, 2006-02-23 at 10:42 +0100, Andi Kleen wrote:
> > On Thursday 23 February 2006 10:30, Arjan van de Ven wrote:
> > > This patch adds a per task-struct cache of a free vma. 
> > > 
> > > In normal operation, it is a really common action during userspace mmap 
> > > or malloc to first allocate a vma, and then find out that it can be merged,
> > > and thus free it again. In fact this is the case roughly 95% of the time.
> > > 
> > > In addition, this patch allows code to "prepopulate" the cache, and
> > > this is done as example for the x86_64 mmap codepath. The advantage of this
> > > prepopulation is that the memory allocation (which is a sleeping operation
> > > due to the GFP_KERNEL flag, potentially causing either a direct sleep or a 
> > > voluntary preempt sleep) will happen before the mmap_sem is taken, and thus 
> > > reduces lock hold time (and thus the contention potential)
> > 
> > The slab fast path doesn't sleep. 
> 
> it does via might_sleep()

Hmm? That shouldn't sleep.

If it takes any time in a real workload then it should move into DEBUG_KERNEL
too. But I doubt it. Something with your analysis is wrong.

-Andi

P.S.: Your email address bounces.