lkml.org 
[lkml]   [2009]   [Dec]   [8]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: [early RFC][PATCH 8/7] vmscan: Don't deactivate many touched page
Date
> On 12/07/2009 06:36 AM, KOSAKI Motohiro wrote:
> >
> > Andrea, Can you please try following patch on your workload?
> >
> >
> > From a7758c66d36a136d5fbbcf0b042839445f0ca522 Mon Sep 17 00:00:00 2001
> > From: KOSAKI Motohiro<kosaki.motohiro@jp.fujitsu.com>
> > Date: Mon, 7 Dec 2009 18:37:20 +0900
> > Subject: [PATCH] [RFC] vmscan: Don't deactivate many touched page
> >
> > Changelog
> > o from andrea's original patch
> > - Rebase topon my patches.
> > - Use list_cut_position/list_splice_tail pair instead
> > list_del/list_add to make pte scan fairness.
> > - Only use max young threshold when soft_try is true.
> > It avoid wrong OOM sideeffect.
> > - Return SWAP_AGAIN instead successful result if max
> > young threshold exceed. It prevent the pages without clear
> > pte young bit will be deactivated wrongly.
> > - Add to treat ksm page logic
>
> I like the concept and your changes, and really only
> have a few small nitpicks :)
>
> First, the VM uses a mix of "referenced", "accessed" and
> "young". We should probably avoid adding "active" to that
> mix, and may even want to think about moving to just one
> or two terms :)

Ah yes, certainly.


> > +#define MAX_YOUNG_BIT_CLEARED 64
> > +/*
> > + * if VM pressure is low and the page have too many active mappings, there isn't
> > + * any reason to continue clear young bit of other ptes. Otherwise,
> > + * - Makes meaningless cpu wasting, many touched page sholdn't be reclaimed.
> > + * - Makes lots IPI for pte change and it might cause another sadly lock
> > + * contention.
> > + */
>
> If VM pressure is low and the page has lots of active users, we only
> clear up to MAX_YOUNG_BIT_CLEARED accessed bits at a time. Clearing
> accessed bits takes CPU time, needs TLB invalidate IPIs and could
> cause lock contention. Since a heavily shared page is very likely
> to be used again soon, the cost outweighs the benefit of making such
> a heavily shared page a candidate for eviction.

Thanks. Will fix.


> > diff --git a/mm/rmap.c b/mm/rmap.c
> > index cfda0a0..f4517f3 100644
> > --- a/mm/rmap.c
> > +++ b/mm/rmap.c
> > @@ -473,6 +473,21 @@ static int wipe_page_reference_anon(struct page *page,
> > ret = wipe_page_reference_one(page, refctx, vma, address);
> > if (ret != SWAP_SUCCESS)
> > break;
> > + if (too_many_young_bit_found(refctx)) {
> > + LIST_HEAD(tmp_list);
> > +
> > + /*
> > + * The scanned ptes move to list tail. it help every ptes
> > + * on this page will be tested by ptep_clear_young().
> > + * Otherwise, this shortcut makes unfair thing.
> > + */
> > + list_cut_position(&tmp_list,
> > + &vma->anon_vma_node,
> > + &anon_vma->head);
> > + list_splice_tail(&tmp_list,&vma->anon_vma_node);
> > + ret = SWAP_AGAIN;
> > + break;
> > + }
>
> I do not understand the unfairness here, since all a page needs
> to stay on the active list is >64 referenced PTEs. It does not
> matter which of the PTEs mapping the page were recently referenced.
>
> However, rotating the anon vmas around may help spread out lock
> pressure in the VM and help things that way, so the code looks
> useful to me.

agreed. I have to rewrite the comment.


> In short, you can give the next version of this patch my
>
> Reviewed-by: Rik van Riel <riel@redhat.com>
>
> All I have are comment nitpicks :)

No. It's really worth.

Thank you.




\
 
 \ /
  Last update: 2009-12-08 07:31    [W:0.064 / U:14.512 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site