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SubjectRe: [PATCH 08/21] mm: Preemptible mmu_gather
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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@chello.nl> 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@kernel.crashing.org>
> > Cc: David Miller <davem@davemloft.net>
> > Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
> > Cc: Russell King <rmk@arm.linux.org.uk>
> > Cc: Paul Mundt <lethal@linux-sh.org>
> > Cc: Jeff Dike <jdike@addtoit.com>
> > Cc: Tony Luck <tony.luck@intel.com>
> > Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
>
> Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
>
> 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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