Messages in this thread | | | Date | Mon, 20 Dec 2010 13:35:26 +0900 | From | KAMEZAWA Hiroyuki <> | Subject | Re: [RFC 5/5] truncate: Remove unnecessary page release |
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On Mon, 20 Dec 2010 11:58:50 +0900 Minchan Kim <minchan.kim@gmail.com> wrote:
> On Mon, Dec 20, 2010 at 11:27 AM, KAMEZAWA Hiroyuki > <kamezawa.hiroyu@jp.fujitsu.com> wrote: > > On Mon, 20 Dec 2010 11:21:52 +0900 (JST) > > KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> wrote: > > > >> > This patch series changes remove_from_page_cache's page ref counting > >> > rule. page cache ref count is decreased in remove_from_page_cache. > >> > So we don't need call again in caller context. > >> > > >> > Cc: Nick Piggin <npiggin@suse.de> > >> > Cc: Al Viro <viro@zeniv.linux.org.uk> > >> > Cc: linux-mm@kvack.org > >> > Signed-off-by: Minchan Kim <minchan.kim@gmail.com> > >> > --- > >> > mm/truncate.c | 1 - > >> > 1 files changed, 0 insertions(+), 1 deletions(-) > >> > > >> > diff --git a/mm/truncate.c b/mm/truncate.c > >> > index 9ee5673..8decb93 100644 > >> > --- a/mm/truncate.c > >> > +++ b/mm/truncate.c > >> > @@ -114,7 +114,6 @@ truncate_complete_page(struct address_space *mapping, struct page *page) > >> > * calls cleancache_put_page (and note page->mapping is now NULL) > >> > */ > >> > cleancache_flush_page(mapping, page); > >> > - page_cache_release(page); /* pagecache ref */ > >> > return 0; > >> > >> Do we _always_ have stable page reference here? IOW, I can assume > >> cleancache_flush_page() doesn't cause NULL deref? > >> > > Hmm, my review was bad. > > > > I think cleancache_flush_page() here should eat (mapping, index) as argument > > rather than "page". > > > > BTW, I can't understand > > == > > void __cleancache_flush_page(struct address_space *mapping, struct page *page) > > { > > /* careful... page->mapping is NULL sometimes when this is called */ > > int pool_id = mapping->host->i_sb->cleancache_poolid; > > struct cleancache_filekey key = { .u.key = { 0 } }; > > == > > > > Why above is safe... > > I think (mapping,index) should be passed instead of page. > > I don't think current code isn't safe. > > void __cleancache_flush_page(struct address_space *mapping, struct page *page) > { > /* careful... page->mapping is NULL sometimes when this is called */ > int pool_id = mapping->host->i_sb->cleancache_poolid; > struct cleancache_filekey key = { .u.key = { 0 } }; > > if (pool_id >= 0) { > VM_BUG_ON(!PageLocked(page)); > > it does check PageLocked. So caller should hold a page reference to > prevent freeing ramined PG_locked > If the caller doesn't hold a ref of page, I think it's BUG of caller. > > In our case, caller calls truncate_complete_page have to make sure it, I think. >
Ah, my point is that this function trust page->index even if page->mapping is reset to NULL. And I'm not sure that there are any race that an other thread add a replacement page for (mapping, index) while a thread call this function.
Thanks, -Kame
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