Re: [Patch 2/3] fast VMA recycling

[Arjan van de Ven <arjan@intel.linux.com>]

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()

> Numbers numbers numbers. What workload? How much did it help? 

see post 0/3

3% on a threaded allocation benchmark (which resembles a webserver with
cgis apparently)