From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-oi0-f71.google.com (mail-oi0-f71.google.com [209.85.218.71]) by kanga.kvack.org (Postfix) with ESMTP id 856646B0279 for ; Wed, 24 May 2017 21:23:08 -0400 (EDT) Received: by mail-oi0-f71.google.com with SMTP id w205so231775997oif.12 for ; Wed, 24 May 2017 18:23:08 -0700 (PDT) Received: from szxga01-in.huawei.com (szxga01-in.huawei.com. [45.249.212.187]) by mx.google.com with ESMTPS id y32si3467557oty.29.2017.05.24.18.23.06 for (version=TLS1 cipher=AES128-SHA bits=128/128); Wed, 24 May 2017 18:23:07 -0700 (PDT) Message-ID: <5926306F.2060205@huawei.com> Date: Thu, 25 May 2017 09:16:31 +0800 From: Xishi Qiu MIME-Version: 1.0 Subject: Re: [Question] Mlocked count will not be decreased References: <85591559-2a99-f46b-7a5a-bc7affb53285@huawei.com> <93f1b063-6288-d109-117d-d3c1cf152a8e@suse.cz> <5925709F.1030105@huawei.com> <5925784E.802@huawei.com> In-Reply-To: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Vlastimil Babka Cc: Yisheng Xie , Kefeng Wang , linux-mm@kvack.org, linux-kernel@vger.kernel.org, zhongjiang On 2017/5/24 21:16, Vlastimil Babka wrote: > On 05/24/2017 02:10 PM, Xishi Qiu wrote: >> On 2017/5/24 19:52, Vlastimil Babka wrote: >> >>> On 05/24/2017 01:38 PM, Xishi Qiu wrote: >>>>> >>>>> Race condition with what? Who else would isolate our pages? >>>>> >>>> >>>> Hi Vlastimil, >>>> >>>> I find the root cause, if the page was not cached on the current cpu, >>>> lru_add_drain() will not push it to LRU. So we should handle fail >>>> case in mlock_vma_page(). >>> >>> Yeah that would explain it. >>> >>>> follow_page_pte() >>>> ... >>>> if (page->mapping && trylock_page(page)) { >>>> lru_add_drain(); /* push cached pages to LRU */ >>>> /* >>>> * Because we lock page here, and migration is >>>> * blocked by the pte's page reference, and we >>>> * know the page is still mapped, we don't even >>>> * need to check for file-cache page truncation. >>>> */ >>>> mlock_vma_page(page); >>>> unlock_page(page); >>>> } >>>> ... >>>> >>>> I think we should add yisheng's patch, also we should add the following change. >>>> I think it is better than use lru_add_drain_all(). >>> >>> I agree about yisheng's fix (but v2 didn't address my comments). I don't >>> think we should add the hunk below, as that deviates from the rest of >>> the design. >> >> Hi Vlastimil, >> >> The rest of the design is that mlock should always success here, right? > > The rest of the design allows a temporary disconnect between mlocked > flag and being placed on unevictable lru. > >> If we don't handle the fail case, the page will be in anon/file lru list >> later when call __pagevec_lru_add(), but NR_MLOCK increased, >> this is wrong, right? > > It's not wrong, the page cannot get evicted even if on wrong lru, so > effectively it's already mlocked. We would be underaccounting NR_MLOCK. > Hi Vlastimil, I'm not quite understand why the page cannot get evicted even if on wrong lru. __isolate_lru_page() will only skip PageUnevictable(page), but this flag has not been set, we only set PageMlocked. Thanks, Xishi Qiu >> Thanks, >> Xishi Qiu >> >>> >>> Thanks, >>> Vlastimil >>> >>>> diff --git a/mm/mlock.c b/mm/mlock.c >>>> index 3d3ee6c..ca2aeb9 100644 >>>> --- a/mm/mlock.c >>>> +++ b/mm/mlock.c >>>> @@ -88,6 +88,11 @@ void mlock_vma_page(struct page *page) >>>> count_vm_event(UNEVICTABLE_PGMLOCKED); >>>> if (!isolate_lru_page(page)) >>>> putback_lru_page(page); >>>> + else { >>>> + ClearPageMlocked(page); >>>> + mod_zone_page_state(page_zone(page), NR_MLOCK, >>>> + -hpage_nr_pages(page)); >>>> + } >>>> } >>>> } >>>> >>>> Thanks, >>>> Xishi Qiu >>>> >>> >>> >>> . >>> >> >> >> >> -- >> 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 >> > > > . > -- 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