Messages in this thread | | | Date | Mon, 12 Dec 2011 10:31:57 -0500 | From | KOSAKI Motohiro <> | Subject | Re: [PATCH v3] mm: simplify find_vma_prev |
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(12/12/11 4:27 AM), KAMEZAWA Hiroyuki wrote: > On Mon, 12 Dec 2011 09:49:30 +0900 > KAMEZAWA Hiroyuki<kamezawa.hiroyu@jp.fujitsu.com> wrote: > >> On Fri, 9 Dec 2011 17:48:40 -0500 >> kosaki.motohiro@gmail.com wrote: >> >>> From: KOSAKI Motohiro<kosaki.motohiro@jp.fujitsu.com> >>> >>> commit 297c5eee37 (mm: make the vma list be doubly linked) added >>> vm_prev member into vm_area_struct. Therefore we can simplify >>> find_vma_prev() by using it. Also, this change help to improve >>> page fault performance because it has strong locality of reference. >>> >>> Signed-off-by: KOSAKI Motohiro<kosaki.motohiro@jp.fujitsu.com> >> >> Reviewed-by: KAMEZAWA Hiroyuki<kamezawa.hiroyu@jp.fujitsu.com> >> > > Hmm, your work remind me of a patch I tried in past. > Here is a refleshed one...how do you think ? > > == > From c0261936fc01322d06425731d33f38b2021e8067 Mon Sep 17 00:00:00 2001 > From: KAMEZAWA Hiroyuki<kamezawa.hiroyu@jp.fujitsu.com> > Date: Mon, 12 Dec 2011 18:31:19 +0900 > Subject: [PATCH] per thread vma cache. > > This is a toy patch. How do you think ? > > This is a patch for per-thread mmap_cache without heavy atomic ops. > > I'm sure overhead of find_vma() is pretty small in usual application > and this will not show good improvement. But I think, if we need > to have cache of vma, it should be per thread rather than per mm.
Agreed. per-thread is better.
> This patch adds thread->mmap_cache, a pointer for vm_area_struct > and update it appropriately. Because we have no refcnt on vm_area_struct, > thread->mmap_cache may be a stale pointer. This patch detects stale > pointer by checking > > - thread->mmap_cache is one of SLABs in vm_area_cachep. > - thread->mmap_cache->vm_mm == mm. > > vma->vm_mm will be cleared before kmem_cache_free() by this patch.
Do you mean the cache can make mishit with unrelated vma when freed vma was reused? If so, it is most tricky part of this patch, I strongly hope you write a comment more.
Thank you.
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