Re: [Patch 2/3] fast VMA recycling

[Christoph Hellwig <hch@infradead.org>]

On Thu, Feb 23, 2006 at 10:48:50AM +0100, 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()

so turn of the voluntary preempt bullshit.