Messages in this thread | | | Date | Wed, 19 Aug 2009 22:00:53 +0800 | From | Wu Fengguang <> | Subject | Re: [RFC] respect the referenced bit of KVM guest pages? |
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On Wed, Aug 19, 2009 at 09:38:05PM +0800, Minchan Kim wrote: > On Wed, Aug 19, 2009 at 10:24 PM, Wu Fengguang<fengguang.wu@intel.com> wrote: > > On Wed, Aug 19, 2009 at 08:25:56PM +0800, Minchan Kim wrote: > >> On Wed, Aug 19, 2009 at 9:10 PM, Wu Fengguang<fengguang.wu@intel.com> wrote: > >> > On Wed, Aug 19, 2009 at 08:05:19PM +0800, KOSAKI Motohiro wrote: > >> >> >> 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@intel.com> > >> >> > >> >> Thanks. > >> >> > >> >> > >> >> > >> >> >> 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? > >> >> > >> >> 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. > >> > >> 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 ? > > > > No, IMHO your patch is simple and good, while KOSAKI's is more > > complete :) > > > > - the try_set_page_mlocked() rename is suitable > > - the call to try_set_page_mlocked() is necessary on try_to_unmap() > > We don't need try_set_page_mlocked call in try_to_unmap. > That's because try_to_unmap_xxx will call try_to_mlock_page if the > page is included in any VM_LOCKED vma. Eventually, It can move > unevictable list.
Yes, indeed!
> > - the "if (VM_LOCKED) referenced = 0" in page_referenced() could > > cover both active/inactive vmscan > > ASAP we set PG_mlocked in page, we can save unnecessary vmscan cost from > active list to inactive list. But I think it's rare case so that there > would be few pages. > So I think that will be not big overhead.
The active list case can be persistent, when the mlocked (but without PG_mlocked) page is executable and referenced by 2+ processes. But I admit that executable pages are relatively rare.
> As I know, Rescue by vmscan page losing the isolation race was the > Lee's design. > But as you pointed out, it have a bug that vmscan can't rescue the > page due to reach try_to_unmap. > > So I think this approach is proper. :)
Now you decide :)
Thanks, Fengguang
> > I did like your proposed > > > > if (sc->order <= PAGE_ALLOC_COSTLY_ORDER && > > - referenced && page_mapping_inuse(page)) > > + referenced && page_mapping_inuse(page) > > + && !(vm_flags & VM_LOCKED)) > > goto activate_locked; > > > > which looks more intuitive and less confusing. > > > > Thanks, > > Fengguang > > > > > > -- > Kind regards, > Minchan Kim -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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