From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Wed, 30 Apr 2008 07:19:32 +0200 From: Nick Piggin Subject: Re: [PATCH] more ZERO_PAGE handling ( was 2.6.24 regression: deadlock on coredump of big process) Message-ID: <20080430051932.GD27652@wotan.suse.de> References: <4815E932.1040903@cybernetics.com> <20080429100048.3e78b1ba.kamezawa.hiroyu@jp.fujitsu.com> <48172C72.1000501@cybernetics.com> <20080430132516.28f1ee0c.kamezawa.hiroyu@jp.fujitsu.com> <4817FDA5.1040702@kolumbus.fi> <20080430141738.e6b80d4b.kamezawa.hiroyu@jp.fujitsu.com> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20080430141738.e6b80d4b.kamezawa.hiroyu@jp.fujitsu.com> Sender: owner-linux-mm@kvack.org Return-Path: To: KAMEZAWA Hiroyuki Cc: Mika =?iso-8859-1?Q?Penttil=E4?= , Tony Battersby , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrew Morton List-ID: On Wed, Apr 30, 2008 at 02:17:38PM +0900, KAMEZAWA Hiroyuki wrote: > On Wed, 30 Apr 2008 08:03:33 +0300 > Mika Penttila wrote: > > > > == > > > @@ -2252,39 +2158,24 @@ static int do_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma, > > > spinlock_t *ptl; > > > { > > > > > > - page_add_new_anon_rmap(page, vma, address); > > > - } else { > > > - /* Map the ZERO_PAGE - vm_page_prot is readonly */ > > > - page = ZERO_PAGE(address); > > > - page_cache_get(page); > > > - entry = mk_pte(page, vma->vm_page_prot); > > > + if (unlikely(anon_vma_prepare(vma))) > > > + goto oom; > > > + page = alloc_zeroed_user_highpage_movable(vma, address); > > > == > > > > > > above change is for avoiding to use ZERO_PAGE at read-page-fault to anonymous > > > vma. This is reasonable I think. But at coredump, tons of read-but-never-written > > > pages can be allocated. > > > == > > > coredump > > > -> get_user_pages() > > > -> follow_page() returns NULL > > > -> handle mm fault > > > -> do_anonymous page. > > > == > > > follow_page() returns ZERO_PAGE only when page table is not avaiable. > > > > > > So, making follow_page() return ZERO_PAGE can be a fix of extra memory > > > consumpstion at core dump. (Maybe someone can think of other fix.) > > > > > > how about this patch ? Could you try ? > > > > > > (I'm sorry but I'll not be active for a week because my servers are powered off.) > > > > > > -Kame > > > > > > > > > > > > But sure we still have to handle the fault for instance swapped pages, > > for other uses of get_user_pages(); > > > Ah, my bad.....how about this ? I changed !pte_present() to pte_none(). > > -Kame > == > follow_page() returns ZERO_PAGE if a page table is not available. > but returns NULL if a page table exists. If NULL, handle_mm_fault() > allocates a new page. > > This behavior increases page consumption at coredump, which tend > to do read-once-but-never-written page fault. This patch is > for avoiding this. I think you still need the pte_present test too, otherwise !present and !none ptes can slip through and be treated as present. Something like this should do: if (!pte_present(pte)) { if (pte_none(pte)) { pte_unmap_unlock goto null_or_zeropage; } goto unlock; } > > Changelog: > - fixed to check pte_none() not !pte_present(). > > > Signed-off-by: KAMEZAWA Hiroyuki > > Index: linux-2.6.25/mm/memory.c > =================================================================== > --- linux-2.6.25.orig/mm/memory.c > +++ linux-2.6.25/mm/memory.c > @@ -926,15 +926,15 @@ struct page *follow_page(struct vm_area_ > page = NULL; > pgd = pgd_offset(mm, address); > if (pgd_none(*pgd) || unlikely(pgd_bad(*pgd))) > - goto no_page_table; > + goto null_or_zeropage; > > pud = pud_offset(pgd, address); > if (pud_none(*pud) || unlikely(pud_bad(*pud))) > - goto no_page_table; > + goto null_or_zeropage; > > pmd = pmd_offset(pud, address); > if (pmd_none(*pmd) || unlikely(pmd_bad(*pmd))) > - goto no_page_table; > + goto null_or_zeropage; > > if (pmd_huge(*pmd)) { > BUG_ON(flags & FOLL_GET); > @@ -947,8 +947,10 @@ struct page *follow_page(struct vm_area_ > goto out; > > pte = *ptep; > - if (!pte_present(pte)) > - goto unlock; > + if (!(flags & FOLL_WRITE) && pte_none(pte)) { > + pte_unmap_unlock(ptep, ptl); > + goto null_or_zeropage; > + } > if ((flags & FOLL_WRITE) && !pte_write(pte)) > goto unlock; > page = vm_normal_page(vma, address, pte); > @@ -968,7 +970,7 @@ unlock: > out: > return page; > > -no_page_table: > +null_or_zeropage: > /* > * When core dumping an enormous anonymous area that nobody > * has touched so far, we don't want to allocate page tables. > > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org