Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753888Ab1FDH7g (ORCPT ); Sat, 4 Jun 2011 03:59:36 -0400 Received: from mail-pw0-f46.google.com ([209.85.160.46]:54706 "EHLO mail-pw0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753458Ab1FDH7f (ORCPT ); Sat, 4 Jun 2011 03:59:35 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=date:from:to:cc:subject:message-id:references:mime-version :content-type:content-disposition:in-reply-to:user-agent; b=G4dB58CKoVCdnZBqJERmXcMaKoatNqIzPclPHAGI65RmbMPjDua1F1vBX6AjYDEP9v XhD4wogmR3/Ny/N/o7svJiFHubtUzEK3iQ9va4er5CNxBhiTBfnIz76C+VgqCYqtkTxD d0neN6sRdScRtScdTOxuy8WL0cApy7XuH0YWE= Date: Sat, 4 Jun 2011 16:59:26 +0900 From: Minchan Kim To: Andrea Arcangeli Cc: Mel Gorman , Mel Gorman , akpm@linux-foundation.org, Ury Stankevich , KOSAKI Motohiro , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH] mm: compaction: Abort compaction if too many pages are isolated and caller is asynchronous Message-ID: <20110604075926.GC4114@barrios-laptop> References: <20110531143734.GB13418@barrios-laptop> <20110531143830.GC13418@barrios-laptop> <20110602182302.GA2802@random.random> <20110602202156.GA23486@barrios-laptop> <20110602214041.GF2802@random.random> <20110602223201.GH2802@random.random> <20110603173707.GL2802@random.random> <20110603180730.GM2802@random.random> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110603180730.GM2802@random.random> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4671 Lines: 113 On Fri, Jun 03, 2011 at 08:07:30PM +0200, Andrea Arcangeli wrote: > On Fri, Jun 03, 2011 at 07:37:07PM +0200, Andrea Arcangeli wrote: > > On Fri, Jun 03, 2011 at 08:01:44AM +0900, Minchan Kim wrote: > > > Do you want this? (it's almost pseudo-code) > > > > Yes that's good idea so we at least take into account if we isolated > > something big, and it's pointless to insist wasting CPU on the tail > > pages and even trace a fail because of tail pages after it. > > > > I introduced a __page_count to increase readability. It's still > > hackish to work on subpages in vmscan.c but at least I added a comment > > and until we serialize destroy_compound_page vs compound_head, I guess > > there's no better way. I didn't attempt to add out of order > > serialization similar to what exists for split_huge_page vs > > compound_trans_head yet, as the page can be allocated or go away from > > under us, in split_huge_page vs compound_trans_head it's simpler > > because both callers are required to hold a pin on the page so the > > page can't go be reallocated and destroyed under it. > > Sent too fast... had to shuffle a few things around... trying again. > > === > Subject: mm: no page_count without a page pin > > From: Andrea Arcangeli > > It's unsafe to run page_count during the physical pfn scan because > compound_head could trip on a dangling pointer when reading page->first_page if > the compound page is being freed by another CPU. Also properly take into > account if we isolated a compound page during the scan and break the loop if > we've isolated enoguh. Introduce __page_count to cleanup some atomic_read from > &page->_count in common code to cleanup. > Patch looks good to me. I have a question. Please see bottom line. In addition, I think this patch have to be divided by 4 patches. 1. fix accounting nu_lumpy_taken, nr_lumpy_dirty on hpage 2. early breaking of isolate_lru_pages if we had enough isolated pages 3. introduce __page_count and cleanup 4. fix page_count usage of subpage in vmscan.c > Signed-off-by: Andrea Arcangeli > --- > arch/powerpc/mm/gup.c | 2 - > arch/powerpc/platforms/512x/mpc512x_shared.c | 2 - > arch/x86/mm/gup.c | 2 - > fs/nilfs2/page.c | 2 - > include/linux/mm.h | 13 ++++++---- > mm/huge_memory.c | 4 +-- > mm/internal.h | 2 - > mm/page_alloc.c | 6 ++-- > mm/swap.c | 4 +-- > mm/vmscan.c | 35 ++++++++++++++++++++------- > 10 files changed, 47 insertions(+), 25 deletions(-) > > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -1047,7 +1047,7 @@ static unsigned long isolate_lru_pages(u > for (scan = 0; scan < nr_to_scan && !list_empty(src); scan++) { > struct page *page; > unsigned long pfn; > - unsigned long end_pfn; > + unsigned long start_pfn, end_pfn; > unsigned long page_pfn; > int zone_id; > > @@ -1087,9 +1087,9 @@ static unsigned long isolate_lru_pages(u > */ > zone_id = page_zone_id(page); > page_pfn = page_to_pfn(page); > - pfn = page_pfn & ~((1 << order) - 1); > - end_pfn = pfn + (1 << order); > - for (; pfn < end_pfn; pfn++) { > + start_pfn = page_pfn & ~((1 << order) - 1); > + end_pfn = start_pfn + (1 << order); > + for (pfn = start_pfn; pfn < end_pfn; pfn++) { > struct page *cursor_page; > > /* The target page is in the block, ignore it. */ > @@ -1116,16 +1116,33 @@ static unsigned long isolate_lru_pages(u > break; > > if (__isolate_lru_page(cursor_page, mode, file) == 0) { > + unsigned int isolated_pages; > list_move(&cursor_page->lru, dst); > mem_cgroup_del_lru(cursor_page); > - nr_taken += hpage_nr_pages(page); > - nr_lumpy_taken++; > + isolated_pages = hpage_nr_pages(page); > + nr_taken += isolated_pages; > + nr_lumpy_taken += isolated_pages; > if (PageDirty(cursor_page)) > - nr_lumpy_dirty++; > + nr_lumpy_dirty += isolated_pages; > scan++; > + pfn += isolated_pages-1; > + VM_BUG_ON(!isolated_pages); > + VM_BUG_ON(isolated_pages > MAX_ORDER_NR_PAGES); What's point of this VM_BUG_ONs? Could you explain what you expect with this VM_BUG_ONs? -- 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/