From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Wed, 30 Apr 2008 13:25:16 +0900 From: KAMEZAWA Hiroyuki Subject: [PATCH] more ZERO_PAGE handling ( was 2.6.24 regression: deadlock on coredump of big process) Message-Id: <20080430132516.28f1ee0c.kamezawa.hiroyu@jp.fujitsu.com> In-Reply-To: <48172C72.1000501@cybernetics.com> References: <4815E932.1040903@cybernetics.com> <20080429100048.3e78b1ba.kamezawa.hiroyu@jp.fujitsu.com> <48172C72.1000501@cybernetics.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Tony Battersby Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Nick Piggin , Andrew Morton List-ID: On Tue, 29 Apr 2008 10:10:58 -0400 Tony Battersby wrote: > > If I leave more memory free by changing the argument to > malloc_all_but_x_mb(), then I have to increase the number of threads > required to trigger the deadlock. Changing the thread stack size via > setrlimit(RLIMIT_STACK) also changes the number of threads that are > required to trigger the deadlock. For example, with > malloc_all_but_x_mb(16) and the default stack size of 8 MB, <= 5 threads > will coredump successfully, and >= 6 threads will deadlock. With > malloc_all_but_x_mb(16) and a reduced stack size of 4096 bytes, <= 8 > threads will coredump successfully, and >= 9 threads will deadlock. > > Also note that the "free" command reports 10 MB free memory while the > program is running before the segfault is triggered. > Hmm, my idea is below. Nick's remove ZERO_PAGE patch includes following change == @@ -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 == follow_page() returns ZERO_PAGE if page table is not available. but returns NULL pte is not presentl. 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_present(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