Messages in this thread | | | Date | Tue, 18 Aug 2009 13:17:34 +0900 | From | Minchan Kim <> | Subject | Re: [RFC] respect the referenced bit of KVM guest pages? |
| |
On Tue, 18 Aug 2009 10:34:38 +0800 Wu Fengguang <fengguang.wu@intel.com> wrote:
> Minchan, > > On Mon, Aug 17, 2009 at 10:33:54PM +0800, Minchan Kim wrote: > > On Sun, Aug 16, 2009 at 8:29 PM, Wu Fengguang<fengguang.wu@intel.com> wrote: > > > On Sun, Aug 16, 2009 at 01:15:02PM +0800, Wu Fengguang wrote: > > >> On Sun, Aug 16, 2009 at 11:53:00AM +0800, Rik van Riel wrote: > > >> > Wu Fengguang wrote: > > >> > > On Fri, Aug 07, 2009 at 05:09:55AM +0800, Jeff Dike wrote: > > >> > >> Side question - > > >> > >> Is there a good reason for this to be in shrink_active_list() > > >> > >> as opposed to __isolate_lru_page? > > >> > >> > > >> > >> if (unlikely(!page_evictable(page, NULL))) { > > >> > >> putback_lru_page(page); > > >> > >> continue; > > >> > >> } > > >> > >> > > >> > >> Maybe we want to minimize the amount of code under the lru lock or > > >> > >> avoid duplicate logic in the isolate_page functions. > > >> > > > > >> > > I guess the quick test means to avoid the expensive page_referenced() > > >> > > call that follows it. But that should be mostly one shot cost - the > > >> > > unevictable pages are unlikely to cycle in active/inactive list again > > >> > > and again. > > >> > > > >> > Please read what putback_lru_page does. > > >> > > > >> > It moves the page onto the unevictable list, so that > > >> > it will not end up in this scan again. > > >> > > >> 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? > > > > I think it's not a big deal. > > Maybe, otherwise I should bring up this issue long time before :) > > > As you mentioned, it's rare case so there would be few pages in active > > list instead of unevictable list. > > Yes. > > > When next time to scan comes, we can try to move the pages into > > unevictable list, again. > > Will PG_mlocked be set by then? Otherwise the situation is not likely > to change and the VM_LOCKED pages may circulate in active/inactive > list for countless times.
PG_mlocked is not important in that case. Important thing is VM_LOCKED vma. I think below annotaion can help you to understand my point. :)
----
/* * called from munlock()/munmap() path with page supposedly on the LRU. * * Note: unlike mlock_vma_page(), we can't just clear the PageMlocked * [in try_to_munlock()] and then attempt to isolate the page. We must * isolate the page to keep others from messing with its unevictable * and mlocked state while trying to munlock. However, we pre-clear the * mlocked state anyway as we might lose the isolation race and we might * not get another chance to clear PageMlocked. If we successfully * isolate the page and try_to_munlock() detects other VM_LOCKED vmas * mapping the page, it will restore the PageMlocked state, unless the page * is mapped in a non-linear vma. So, we go ahead and SetPageMlocked(), * perhaps redundantly. * If we lose the isolation race, and the page is mapped by other VM_LOCKED * vmas, we'll detect this in vmscan--via try_to_munlock() or try_to_unmap() * either of which will restore the PageMlocked state by calling * mlock_vma_page() above, if it can grab the vma's mmap sem. */ static void munlock_vma_page(struct page *page) { ...
-- 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/
| |