From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,UNPARSEABLE_RELAY, URIBL_BLOCKED autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 71938C282DD for ; Wed, 24 Apr 2019 00:22:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4731F218DA for ; Wed, 24 Apr 2019 00:22:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728947AbfDXAWx (ORCPT ); Tue, 23 Apr 2019 20:22:53 -0400 Received: from out30-44.freemail.mail.aliyun.com ([115.124.30.44]:39771 "EHLO out30-44.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726339AbfDXAWx (ORCPT ); Tue, 23 Apr 2019 20:22:53 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R281e4;CH=green;DM=||false|;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e07487;MF=yang.shi@linux.alibaba.com;NM=1;PH=DS;RN=7;SR=0;TI=SMTPD_---0TQ5BmiI_1556065358; Received: from US-143344MP.local(mailfrom:yang.shi@linux.alibaba.com fp:SMTPD_---0TQ5BmiI_1556065358) by smtp.aliyun-inc.com(127.0.0.1); Wed, 24 Apr 2019 08:22:48 +0800 Subject: Re: [v2 PATCH] mm: thp: fix false negative of shmem vma's THP eligibility From: Yang Shi To: Michal Hocko Cc: vbabka@suse.cz, rientjes@google.com, kirill@shutemov.name, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <1556037781-57869-1-git-send-email-yang.shi@linux.alibaba.com> <20190423175252.GP25106@dhcp22.suse.cz> <6004f688-99d8-3f8c-a106-66ee52c1f0ee@linux.alibaba.com> Message-ID: Date: Tue, 23 Apr 2019 17:22:36 -0700 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.12; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: <6004f688-99d8-3f8c-a106-66ee52c1f0ee@linux.alibaba.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 4/23/19 11:34 AM, Yang Shi wrote: > > > On 4/23/19 10:52 AM, Michal Hocko wrote: >> On Wed 24-04-19 00:43:01, Yang Shi wrote: >>> The commit 7635d9cbe832 ("mm, thp, proc: report THP eligibility for >>> each >>> vma") introduced THPeligible bit for processes' smaps. But, when >>> checking >>> the eligibility for shmem vma, __transparent_hugepage_enabled() is >>> called to override the result from shmem_huge_enabled().  It may result >>> in the anonymous vma's THP flag override shmem's.  For example, >>> running a >>> simple test which create THP for shmem, but with anonymous THP >>> disabled, >>> when reading the process's smaps, it may show: >>> >>> 7fc92ec00000-7fc92f000000 rw-s 00000000 00:14 27764 /dev/shm/test >>> Size:               4096 kB >>> ... >>> [snip] >>> ... >>> ShmemPmdMapped:     4096 kB >>> ... >>> [snip] >>> ... >>> THPeligible:    0 >>> >>> And, /proc/meminfo does show THP allocated and PMD mapped too: >>> >>> ShmemHugePages:     4096 kB >>> ShmemPmdMapped:     4096 kB >>> >>> This doesn't make too much sense.  The anonymous THP flag should not >>> intervene shmem THP.  Calling shmem_huge_enabled() with checking >>> MMF_DISABLE_THP sounds good enough.  And, we could skip stack and >>> dax vma check since we already checked if the vma is shmem already. >> Kirill, can we get a confirmation that this is really intended behavior >> rather than an omission please? Is this documented? What is a global >> knob to simply disable THP system wise? >> >> I have to say that the THP tuning API is one giant mess :/ >> >> Btw. this patch also seem to fix khugepaged behavior because it >> previously >> ignored both VM_NOHUGEPAGE and MMF_DISABLE_THP. Second look shows this is not ignored. hugepage_vma_check() would check this for both anonymous vma and shmem vma before scanning. It is called before shmem_huge_enabled(). > > Aha, I didn't notice this. It looks we need separate the patch to fix > that khugepaged problem for both 5.1-rc and LTS. > >> >>> Fixes: 7635d9cbe832 ("mm, thp, proc: report THP eligibility for each >>> vma") >>> Cc: Michal Hocko >>> Cc: Vlastimil Babka >>> Cc: David Rientjes >>> Cc: Kirill A. Shutemov >>> Signed-off-by: Yang Shi >>> --- >>> v2: Check VM_NOHUGEPAGE per Michal Hocko >>> >>>   mm/huge_memory.c | 4 ++-- >>>   mm/shmem.c       | 3 +++ >>>   2 files changed, 5 insertions(+), 2 deletions(-) >>> >>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c >>> index 165ea46..5881e82 100644 >>> --- a/mm/huge_memory.c >>> +++ b/mm/huge_memory.c >>> @@ -67,8 +67,8 @@ bool transparent_hugepage_enabled(struct >>> vm_area_struct *vma) >>>   { >>>       if (vma_is_anonymous(vma)) >>>           return __transparent_hugepage_enabled(vma); >>> -    if (vma_is_shmem(vma) && shmem_huge_enabled(vma)) >>> -        return __transparent_hugepage_enabled(vma); >>> +    if (vma_is_shmem(vma)) >>> +        return shmem_huge_enabled(vma); >>>         return false; >>>   } >>> diff --git a/mm/shmem.c b/mm/shmem.c >>> index 2275a0f..6f09a31 100644 >>> --- a/mm/shmem.c >>> +++ b/mm/shmem.c >>> @@ -3873,6 +3873,9 @@ bool shmem_huge_enabled(struct vm_area_struct >>> *vma) >>>       loff_t i_size; >>>       pgoff_t off; >>>   +    if ((vma->vm_flags & VM_NOHUGEPAGE) || >>> +        test_bit(MMF_DISABLE_THP, &vma->vm_mm->flags)) >>> +        return false; >>>       if (shmem_huge == SHMEM_HUGE_FORCE) >>>           return true; >>>       if (shmem_huge == SHMEM_HUGE_DENY) >>> -- >>> 1.8.3.1 >>> >