Messages in this thread | | | Date | Wed, 8 Dec 2010 09:56:42 +0900 | From | KAMEZAWA Hiroyuki <> | Subject | Re: [PATCH v4 2/7] deactivate invalidated pages |
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On Wed, 8 Dec 2010 07:51:25 +0900 Minchan Kim <minchan.kim@gmail.com> wrote:
> On Wed, Dec 8, 2010 at 12:56 AM, Johannes Weiner <hannes@cmpxchg.org> wrote: > > On Wed, Dec 08, 2010 at 12:26:25AM +0900, Minchan Kim wrote: > >> On Tue, Dec 07, 2010 at 04:19:39PM +0100, Johannes Weiner wrote: > >> > On Wed, Dec 08, 2010 at 12:07:10AM +0900, Minchan Kim wrote: > >> > > On Tue, Dec 07, 2010 at 03:49:24PM +0100, Johannes Weiner wrote: > >> > > > On Mon, Dec 06, 2010 at 02:29:10AM +0900, Minchan Kim wrote: > >> > > > > Changelog since v3: > >> > > > > - Change function comments - suggested by Johannes > >> > > > > - Change function name - suggested by Johannes > >> > > > > - add only dirty/writeback pages to deactive pagevec > >> > > > > >> > > > Why the extra check? > >> > > > > >> > > > > @@ -359,8 +360,16 @@ unsigned long invalidate_mapping_pages(struct address_space *mapping, > >> > > > > if (lock_failed) > >> > > > > continue; > >> > > > > > >> > > > > - ret += invalidate_inode_page(page); > >> > > > > - > >> > > > > + ret = invalidate_inode_page(page); > >> > > > > + /* > >> > > > > + * If the page is dirty or under writeback, we can not > >> > > > > + * invalidate it now. But we assume that attempted > >> > > > > + * invalidation is a hint that the page is no longer > >> > > > > + * of interest and try to speed up its reclaim. > >> > > > > + */ > >> > > > > + if (!ret && (PageDirty(page) || PageWriteback(page))) > >> > > > > + deactivate_page(page); > >> > > > > >> > > > The writeback completion handler does not take the page lock, so you > >> > > > can still miss pages that finish writeback before this test, no? > >> > > > >> > > Yes. but I think it's rare and even though it happens, it's not critical. > >> > > > > >> > > > Can you explain why you felt the need to add these checks? > >> > > > >> > > invalidate_inode_page can return 0 although the pages is !{dirty|writeback}. > >> > > Look invalidate_complete_page. As easiest example, if the page has buffer and > >> > > try_to_release_page can't release the buffer, it could return 0. > >> > > >> > Ok, but somebody still tried to truncate the page, so why shouldn't we > >> > try to reclaim it? The reason for deactivating at this location is > >> > that truncation is a strong hint for reclaim, not that it failed due > >> > to dirty/writeback pages. > >> > > >> > What's the problem with deactivating pages where try_to_release_page() > >> > failed? > >> > >> If try_to_release_page fails and the such pages stay long time in pagevec, > >> pagevec drain often happens. > > > > You mean because the pagevec becomes full more often? These are not > > many pages you get extra without the checks, the race window is very > > small after all. > > Right. > It was a totally bad answer. The work in midnight makes my mind to be hurt. :) > > Another point is that we can move such pages(!try_to_release_page, > someone else holding the ref) into tail of inactive. > We can't expect such pages will be freed sooner or later and it can > stir lru pages unnecessary. > On the other hand it's a _really_ rare so couldn't we move the pages into tail? > If it can be justified, I will remove the check. > What do you think about it? >
I wonder ...how about adding "victim" list for "Reclaim" pages ? Then, we don't need extra LRU rotation.
Thanks, -Kame
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