From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1161054AbcFQMVP (ORCPT ); Fri, 17 Jun 2016 08:21:15 -0400 Received: from mail-wm0-f66.google.com ([74.125.82.66]:33576 "EHLO mail-wm0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753506AbcFQMVO (ORCPT ); Fri, 17 Jun 2016 08:21:14 -0400 Date: Fri, 17 Jun 2016 14:21:11 +0200 From: Michal Hocko To: zhongjiang Cc: mike.kravetz@oracle.com, akpm@linux-foundation.org, kirill@shutemov.name, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm: fix account pmd page to the process Message-ID: <20160617122109.GE21670@dhcp22.suse.cz> References: <1466164575-13578-1-git-send-email-zhongjiang@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1466164575-13578-1-git-send-email-zhongjiang@huawei.com> User-Agent: Mutt/1.6.0 (2016-04-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri 17-06-16 19:56:15, zhongjiang wrote: > From: zhong jiang > > hen a process acquire a pmd table shared by other process, we > increase the account to current process. otherwise, a race result > in other tasks have set the pud entry. so it no need to increase it. I have really hard time to understand (well even to parse) the changelog. What do you think about the following? " huge_pmd_share accounts the number of pmds incorrectly when it races with a parallel pud instantiation. vma_interval_tree_foreach will increase the counter but then has to recheck the pud with the pte lock held and the back off path should drop the increment. The previous code would lead to an elevated pmd count which shouldn't be very harmful (check_mm() might complain and oom_badness() might be marginally confused) but this is worth fixing. " But please note that I am still not 100% sure the race is real. > > Signed-off-by: zhong jiang > --- > mm/hugetlb.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/hugetlb.c b/mm/hugetlb.c > index 19d0d08..3072857 100644 > --- a/mm/hugetlb.c > +++ b/mm/hugetlb.c > @@ -4191,7 +4191,7 @@ pte_t *huge_pmd_share(struct mm_struct *mm, unsigned long addr, pud_t *pud) > (pmd_t *)((unsigned long)spte & PAGE_MASK)); > } else { > put_page(virt_to_page(spte)); > - mm_inc_nr_pmds(mm); > + mm_dec_nr_pmds(mm); > } > spin_unlock(ptl); > out: > -- > 1.8.3.1 -- Michal Hocko SUSE Labs