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Date: Mon, 20 Dec 2010 17:09:11 +0900 From: Minchan Kim <minchan.kim@...il.com> To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> Cc: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>, Andrew Morton <akpm@...ux-foundation.org>, linux-mm <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>, Nick Piggin <npiggin@...e.de>, Al Viro <viro@...iv.linux.org.uk> Subject: Re: [RFC 5/5] truncate: Remove unnecessary page release On Mon, Dec 20, 2010 at 1:35 PM, KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote: > On Mon, 20 Dec 2010 11:58:50 +0900 > Minchan Kim <minchan.kim@...il.com> wrote: > >> On Mon, Dec 20, 2010 at 11:27 AM, KAMEZAWA Hiroyuki >> <kamezawa.hiroyu@...fujitsu.com> wrote: >> > On Mon, 20 Dec 2010 11:21:52 +0900 (JST) >> > KOSAKI Motohiro <kosaki.motohiro@...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@...e.de> >> >> > Cc: Al Viro <viro@...iv.linux.org.uk> >> >> > Cc: linux-mm@...ck.org >> >> > Signed-off-by: Minchan Kim <minchan.kim@...il.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. Because the page is locked and is detached from page cache, I guess it's no problem. Anyway, I think It's off-topic. > > Thanks, > -Kame > > > > -- Kind regards, Minchan Kim -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.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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