From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wr0-f198.google.com (mail-wr0-f198.google.com [209.85.128.198]) by kanga.kvack.org (Postfix) with ESMTP id 5759B6B0003 for ; Tue, 22 May 2018 15:31:42 -0400 (EDT) Received: by mail-wr0-f198.google.com with SMTP id c56-v6so15334402wrc.5 for ; Tue, 22 May 2018 12:31:42 -0700 (PDT) Received: from mx0b-00082601.pphosted.com (mx0b-00082601.pphosted.com. [67.231.153.30]) by mx.google.com with ESMTPS id u22-v6si7566359lfc.401.2018.05.22.12.31.39 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 22 May 2018 12:31:40 -0700 (PDT) From: Song Liu Subject: Re: [PATCH] mm/THP: use hugepage_vma_check() in khugepaged_enter_vma_merge() Date: Tue, 22 May 2018 19:31:31 +0000 Message-ID: <714CDE40-F3F2-4366-8765-C738EC66D8FD@fb.com> References: <20180521193853.3089484-1-songliubraving@fb.com> <20180522121319.GB30663@dhcp22.suse.cz> In-Reply-To: <20180522121319.GB30663@dhcp22.suse.cz> Content-Language: en-US Content-Type: text/plain; charset="us-ascii" Content-ID: Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: "linux-mm@kvack.org" , Kernel Team , Linux Kernel Mailing List , "Kirill A. Shutemov" On May 22, 2018, at 5:13 AM, Michal Hocko wrote: >=20 > [CC Kirill] >=20 > On Mon 21-05-18 12:38:53, Song Liu wrote: >> khugepaged_enter_vma_merge() is using a different approach to check >> whether a vma is valid for khugepaged_enter(): >>=20 >> if (!vma->anon_vma) >> /* >> * Not yet faulted in so we will register later in the >> * page fault if needed. >> */ >> return 0; >> if (vma->vm_ops || (vm_flags & VM_NO_KHUGEPAGED)) >> /* khugepaged not yet working on file or special mappings */ >> return 0; >>=20 >> This check has some problems. One of the obvious problems is that >> it doesn't check shmem_file(), so that vma backed with shmem files >> will not call khugepaged_enter(). >>=20 >> This patch fixes these problems by reusing hugepage_vma_check() in >> khugepaged_enter_vma_merge(). >=20 > It would be great to be more explicit about what are the actual > consequences. khugepaged_enter_vma_merge is called from multiple > context. Some of then do not really care about !anon case (e.g. stack > expansion). hugepage_madvise is quite convoluted so I am not really sure > from a quick look (are we simply not going to merge vmas even if we > could?). Yes, it does fix madvise for shmem with huge=3Dadvise option. I had made a mistake in this version. I will send v2 with the more details on what is fixed.=20 > Have you noticed this by a code inspection or you have seen this > happening in real workloads (aka, is this worth backporting to stable > trees)? I noticed this when reading the code. I think this might worth back=20 porting. However, I don't know whether it fixes anything else other than shmem, so I am not sure which versions need this fix.=20 Thanks, Song >> Signed-off-by: Song Liu >> --- >> mm/khugepaged.c | 12 ++++-------- >> 1 file changed, 4 insertions(+), 8 deletions(-) >>=20 >> diff --git a/mm/khugepaged.c b/mm/khugepaged.c >> index d7b2a4b..e50c2bd 100644 >> --- a/mm/khugepaged.c >> +++ b/mm/khugepaged.c >> @@ -430,18 +430,14 @@ int __khugepaged_enter(struct mm_struct *mm) >> return 0; >> } >>=20 >> +static bool hugepage_vma_check(struct vm_area_struct *vma); >> + >> int khugepaged_enter_vma_merge(struct vm_area_struct *vma, >> unsigned long vm_flags) >> { >> unsigned long hstart, hend; >> - if (!vma->anon_vma) >> - /* >> - * Not yet faulted in so we will register later in the >> - * page fault if needed. >> - */ >> - return 0; >> - if (vma->vm_ops || (vm_flags & VM_NO_KHUGEPAGED)) >> - /* khugepaged not yet working on file or special mappings */ >> + >> + if (!hugepage_vma_check(vma)) >> return 0; >> hstart =3D (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK; >> hend =3D vma->vm_end & HPAGE_PMD_MASK; >> --=20 >> 2.9.5 >=20 > --=20 > Michal Hocko > SUSE Labs