Re: [PATCH 08/21] mm: Preemptible mmu_gather

[Peter Zijlstra]

On Mon, 2010-11-29 at 11:53 +0900, KAMEZAWA Hiroyuki wrote:
> On Fri, 26 Nov 2010 15:38:51 +0100
> Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> wrote:
> 
> > Make mmu_gather preemptible by using a small on stack list and use
> > an option allocation to speed things up.
> > 
> > Preemptible mmu_gather is desired in general and usable once
> > i_mmap_lock becomes a mutex. Doing it before the mutex conversion
> > saves us from having to rework the code by moving the mmu_gather
> > bits inside the i_mmap_lock.
> > 
> > Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
> > Cc: David Miller <davem@xxxxxxxxxxxxx>
> > Cc: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
> > Cc: Russell King <rmk@xxxxxxxxxxxxxxxx>
> > Cc: Paul Mundt <lethal@xxxxxxxxxxxx>
> > Cc: Jeff Dike <jdike@xxxxxxxxxxx>
> > Cc: Tony Luck <tony.luck@xxxxxxxxx>
> > Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
> 
> Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
> 
> Interesting, Hmm, how about using the 1st freed pages as tlb->pages
> rathet than calling alloc_page() ? no benefits ?

We could try that, but we need to be careful there, you need to wait
till after the TLB invalidate and possibly an RCU period for the
page-directory pages (sparc/powerpc).

So doing an optimistic allocation before the TLB invalidate seems saner.

Also, see patch 20.
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