From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f69.google.com (mail-wm0-f69.google.com [74.125.82.69]) by kanga.kvack.org (Postfix) with ESMTP id 664BD6B0286 for ; Tue, 22 May 2018 08:13:22 -0400 (EDT) Received: by mail-wm0-f69.google.com with SMTP id y82-v6so8400901wmb.5 for ; Tue, 22 May 2018 05:13:22 -0700 (PDT) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id v22-v6si3365810eda.271.2018.05.22.05.13.20 for (version=TLS1 cipher=AES128-SHA bits=128/128); Tue, 22 May 2018 05:13:21 -0700 (PDT) Date: Tue, 22 May 2018 14:13:20 +0200 From: Michal Hocko Subject: Re: [PATCH] mm/THP: use hugepage_vma_check() in khugepaged_enter_vma_merge() Message-ID: <20180522121319.GB30663@dhcp22.suse.cz> References: <20180521193853.3089484-1-songliubraving@fb.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180521193853.3089484-1-songliubraving@fb.com> Sender: owner-linux-mm@kvack.org List-ID: To: Song Liu Cc: linux-mm@kvack.org, kernel-team@fb.com, linux-kernel@vger.kernel.org, "Kirill A. Shutemov" [CC Kirill] 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(): > > 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; > > 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(). > > This patch fixes these problems by reusing hugepage_vma_check() in > khugepaged_enter_vma_merge(). 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?). 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)? > Signed-off-by: Song Liu > --- > mm/khugepaged.c | 12 ++++-------- > 1 file changed, 4 insertions(+), 8 deletions(-) > > 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; > } > > +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 = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK; > hend = vma->vm_end & HPAGE_PMD_MASK; > -- > 2.9.5 -- Michal Hocko SUSE Labs