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[195.135.220.15]) by mx.google.com with ESMTPS id j2si2313283ejn.201.2019.04.22.23.50.25 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 22 Apr 2019 23:50:25 -0700 (PDT) Received-SPF: softfail (google.com: domain of transitioning mhocko@kernel.org does not designate 195.135.220.15 as permitted sender) client-ip=195.135.220.15; Authentication-Results: mx.google.com; spf=softfail (google.com: domain of transitioning mhocko@kernel.org does not designate 195.135.220.15 as permitted sender) smtp.mailfrom=mhocko@kernel.org; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=kernel.org X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 8BB55AE32; Tue, 23 Apr 2019 06:50:24 +0000 (UTC) Date: Tue, 23 Apr 2019 08:50:23 +0200 From: Michal Hocko To: Yang Shi Cc: vbabka@suse.cz, rientjes@google.com, kirill@shutemov.name, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm: thp: fix false negative of shmem vma's THP eligibility Message-ID: <20190423065023.GA25106@dhcp22.suse.cz> References: <1555971893-52276-1-git-send-email-yang.shi@linux.alibaba.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1555971893-52276-1-git-send-email-yang.shi@linux.alibaba.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue 23-04-19 06:24:53, 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. Hmm, I was under impression that thw global sysfs is not anonymous memory specific and it overrides whatever sysfs comes with. Isn't ignoring the global setting a bug in the shmemfs allocation paths? Kirill what is the actual semantic here? > 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. Even if I am wrong about the /sys/kernel/mm/transparent_hugepage/enabled being the global setting for _all_ THP then this patch is not sufficient because it doesn't reflect VM_NOHUGEPAGE. > > 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 > --- > mm/huge_memory.c | 4 ++-- > mm/shmem.c | 2 ++ > 2 files changed, 4 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..be15e9b 100644 > --- a/mm/shmem.c > +++ b/mm/shmem.c > @@ -3873,6 +3873,8 @@ bool shmem_huge_enabled(struct vm_area_struct *vma) > loff_t i_size; > pgoff_t off; > > + if (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 > -- Michal Hocko SUSE Labs