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Date: Wed, 19 Aug 2009 20:01:17 +0800
From: Wu Fengguang <fengguang.wu@...el.com>
To: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc: Rik van Riel <riel@...hat.com>, Jeff Dike <jdike@...toit.com>,
Avi Kivity <avi@...hat.com>,
Andrea Arcangeli <aarcange@...hat.com>,
"Yu, Wilfred" <wilfred.yu@...el.com>,
"Kleen, Andi" <andi.kleen@...el.com>,
Hugh Dickins <hugh.dickins@...cali.co.uk>,
Andrew Morton <akpm@...ux-foundation.org>,
Christoph Lameter <cl@...ux-foundation.org>,
Mel Gorman <mel@....ul.ie>,
LKML <linux-kernel@...r.kernel.org>,
linux-mm <linux-mm@...ck.org>
Subject: Re: [RFC] respect the referenced bit of KVM guest pages?
On Tue, Aug 18, 2009 at 11:57:54PM +0800, KOSAKI Motohiro wrote:
> > > Yes it does. I said 'mostly' because there is a small hole that an
> > > unevictable page may be scanned but still not moved to unevictable
> > > list: when a page is mapped in two places, the first pte has the
> > > referenced bit set, the _second_ VMA has VM_LOCKED bit set, then
> > > page_referenced() will return 1 and shrink_page_list() will move it
> > > into active list instead of unevictable list. Shall we fix this rare
> > > case?
> >
> > How about this fix?
>
> Good spotting.
> Yes, this is rare case. but I also don't think your patch introduce
> performance degression.
Thanks.
> However, I think your patch have one bug.
Hehe, sorry for being careless :)
> >
> > ---
> > mm: stop circulating of referenced mlocked pages
> >
> > Signed-off-by: Wu Fengguang <fengguang.wu@...el.com>
> > ---
> >
> > --- linux.orig/mm/rmap.c 2009-08-16 19:11:13.000000000 +0800
> > +++ linux/mm/rmap.c 2009-08-16 19:22:46.000000000 +0800
> > @@ -358,6 +358,7 @@ static int page_referenced_one(struct pa
> > */
> > if (vma->vm_flags & VM_LOCKED) {
> > *mapcount = 1; /* break early from loop */
> > + *vm_flags |= VM_LOCKED;
> > goto out_unmap;
> > }
> >
> > @@ -482,6 +483,8 @@ static int page_referenced_file(struct p
> > }
> >
> > spin_unlock(&mapping->i_mmap_lock);
> > + if (*vm_flags & VM_LOCKED)
> > + referenced = 0;
> > return referenced;
> > }
> >
>
> page_referenced_file?
> I think we should change page_referenced().
Yeah, good catch.
>
> Instead, How about this?
> ==============================================
>
> Subject: [PATCH] mm: stop circulating of referenced mlocked pages
>
> Currently, mlock() systemcall doesn't gurantee to mark the page PG_Mlocked
mark PG_mlocked
> because some race prevent page grabbing.
> In that case, instead vmscan move the page to unevictable lru.
>
> However, Recently Wu Fengguang pointed out current vmscan logic isn't so
> efficient.
> mlocked page can move circulatly active and inactive list because
> vmscan check the page is referenced _before_ cull mlocked page.
>
> Plus, vmscan should mark PG_Mlocked when cull mlocked page.
PG_mlocked
> Otherwise vm stastics show strange number.
>
> This patch does that.
Reviewed-by: Wu Fengguang <fengguang.wu@...el.com>
> Reported-by: Wu Fengguang <fengguang.wu@...el.com>
> Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
> ---
> mm/internal.h | 5 +++--
> mm/rmap.c | 8 +++++++-
> mm/vmscan.c | 2 +-
> 3 files changed, 11 insertions(+), 4 deletions(-)
>
> Index: b/mm/internal.h
> ===================================================================
> --- a/mm/internal.h 2009-06-26 21:06:43.000000000 +0900
> +++ b/mm/internal.h 2009-08-18 23:31:11.000000000 +0900
> @@ -91,7 +91,8 @@ static inline void unevictable_migrate_p
> * to determine if it's being mapped into a LOCKED vma.
> * If so, mark page as mlocked.
> */
> -static inline int is_mlocked_vma(struct vm_area_struct *vma, struct page *page)
> +static inline int try_set_page_mlocked(struct vm_area_struct *vma,
> + struct page *page)
> {
> VM_BUG_ON(PageLRU(page));
>
> @@ -144,7 +145,7 @@ static inline void mlock_migrate_page(st
> }
>
> #else /* CONFIG_HAVE_MLOCKED_PAGE_BIT */
> -static inline int is_mlocked_vma(struct vm_area_struct *v, struct page *p)
> +static inline int try_set_page_mlocked(struct vm_area_struct *v, struct page *p)
> {
> return 0;
> }
> Index: b/mm/rmap.c
> ===================================================================
> --- a/mm/rmap.c 2009-08-18 19:48:14.000000000 +0900
> +++ b/mm/rmap.c 2009-08-18 23:47:34.000000000 +0900
> @@ -362,7 +362,9 @@ static int page_referenced_one(struct pa
> * unevictable list.
> */
> if (vma->vm_flags & VM_LOCKED) {
> - *mapcount = 1; /* break early from loop */
> + *mapcount = 1; /* break early from loop */
> + *vm_flags |= VM_LOCKED; /* for prevent to move active list */
> + try_set_page_mlocked(vma, page);
That call is not absolutely necessary?
Thanks,
Fengguang
> goto out_unmap;
> }
>
> @@ -531,6 +533,9 @@ int page_referenced(struct page *page,
> if (page_test_and_clear_young(page))
> referenced++;
>
> + if (unlikely(*vm_flags & VM_LOCKED))
> + referenced = 0;
> +
> return referenced;
> }
>
> @@ -784,6 +789,7 @@ static int try_to_unmap_one(struct page
> */
> if (!(flags & TTU_IGNORE_MLOCK)) {
> if (vma->vm_flags & VM_LOCKED) {
> + try_set_page_mlocked(vma, page);
> ret = SWAP_MLOCK;
> goto out_unmap;
> }
> Index: b/mm/vmscan.c
> ===================================================================
> --- a/mm/vmscan.c 2009-08-18 19:48:14.000000000 +0900
> +++ b/mm/vmscan.c 2009-08-18 23:30:51.000000000 +0900
> @@ -2666,7 +2666,7 @@ int page_evictable(struct page *page, st
> if (mapping_unevictable(page_mapping(page)))
> return 0;
>
> - if (PageMlocked(page) || (vma && is_mlocked_vma(vma, page)))
> + if (PageMlocked(page) || (vma && try_set_page_mlocked(vma, page)))
> return 0;
>
> return 1;
>
>
>
>
>
>
>
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