Re: [RFC] respect the referenced bit of KVM guest pages?

On Wed, Aug 19, 2009 at 10:19 PM, KOSAKI
Motohiro[off-list ref] wrote:

2009/8/19 Minchan Kim [off-list ref]:

quoted

On Wed, Aug 19, 2009 at 9:10 PM, Wu Fengguang[off-list ref] wrote:

quoted

On Wed, Aug 19, 2009 at 08:05:19PM +0800, KOSAKI Motohiro wrote:

quoted

quoted

quoted

page_referenced_file?
I think we should change page_referenced().

Yeah, good catch.

quoted

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

quoted

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

quoted

Otherwise vm stastics show strange number.

This patch does that.

Reviewed-by: Wu Fengguang <redacted>

Thanks.

quoted

quoted

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 */

quoted

+             try_set_page_mlocked(vma, page);

That call is not absolutely necessary?

Why? I haven't catch your point.

Because we'll eventually hit another try_set_page_mlocked() when
trying to unmap the page. Ie. duplicated with another call you added
in this patch.

Correct.

quoted

Yes. we don't have to call it and we can make patch simple.
I already sent patch on yesterday.

http://marc.info/?l=linux-mm&m=125059325722370&w=2

I think It's more simple than KOSAKI's idea.
Is any problem in my patch ?

Hmm, I think

1. Anyway, we need turn on PG_mlock.

I add my patch again to explain.

diff --git a/mm/rmap.c b/mm/rmap.c
index ed63894..283266c 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c

@@ -358,6 +358,7 @@ static int page_referenced_one(struct page *page,
         */
        if (vma->vm_flags & VM_LOCKED) {
                *mapcount = 1;  /* break early from loop */
+               *vm_flags |= VM_LOCKED;
                goto out_unmap;
        }

diff --git a/mm/vmscan.c b/mm/vmscan.c
index d224b28..d156e1d 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c

@@ -632,7 +632,8 @@ static unsigned long shrink_page_list(struct

list_head *page_list,
                                                sc->mem_cgroup, &vm_flags);
                /* In active use or really unfreeable?  Activate it. */
                if (sc->order <= PAGE_ALLOC_COSTLY_ORDER &&
-                                       referenced && page_mapping_inuse(page))
+                                       referenced && page_mapping_inuse(page)
+                                       && !(vm_flags & VM_LOCKED))
                        goto activate_locked;

By this check, the page can be reached at try_to_unmap after
page_referenced in shrink_page_list. At that time PG_mlocked will be
set.

2. PG_mlock prevent livelock because page_evictable() check is called
at very early in shrink_page_list().

-- 
Kind regards,
Minchan Kim

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