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id 38828B12A; Thu, 18 Jul 2019 21:52:06 +0000 (UTC) Subject: Re: [v3 PATCH 2/2] mm: thp: fix false negative of shmem vma's THP eligibility To: Andrew Morton , Yang Shi Cc: hughd@google.com, kirill.shutemov@linux.intel.com, mhocko@suse.com, rientjes@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <1560401041-32207-1-git-send-email-yang.shi@linux.alibaba.com> <1560401041-32207-3-git-send-email-yang.shi@linux.alibaba.com> <4a07a6b8-8ff2-419c-eac8-3e7dc17670df@suse.cz> <5dde4380-68b4-66ee-2c3c-9b9da0c243ca@linux.alibaba.com> <20190718144459.7a20ac42ee16e093bdfcfab4@linux-foundation.org> From: Vlastimil Babka Openpgp: preference=signencrypt Autocrypt: addr=vbabka@suse.cz; prefer-encrypt=mutual; keydata= mQINBFZdmxYBEADsw/SiUSjB0dM+vSh95UkgcHjzEVBlby/Fg+g42O7LAEkCYXi/vvq31JTB KxRWDHX0R2tgpFDXHnzZcQywawu8eSq0LxzxFNYMvtB7sV1pxYwej2qx9B75qW2plBs+7+YB 87tMFA+u+L4Z5xAzIimfLD5EKC56kJ1CsXlM8S/LHcmdD9Ctkn3trYDNnat0eoAcfPIP2OZ+ 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xVKRSg3I2m+DUTVqBy7Lixo73hnW69kSjtqCeamY/NSu6LNP+b0wAOKhwz9hBEwEHLp05+mj 5ZFJyfGsOiNUcMoO/17FO4EBxSDP3FDLllpuzlFD7SXkfJaMWYmXIlO0jLzdfwfcnDzBbPwO hBM8hvtsyq8lq8vJOxv6XD6xcTtj5Az8t2JjdUX6SF9hxJpwhBU0wrCoGDkWp4Bbv6jnF7zP Nzftr4l8RuJoywDIiJpdaNpSlXKpj/K6KrnyAI/joYc7 Message-ID: Date: Thu, 18 Jul 2019 23:52:04 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.2 MIME-Version: 1.0 In-Reply-To: <20190718144459.7a20ac42ee16e093bdfcfab4@linux-foundation.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 7/18/19 11:44 PM, Andrew Morton wrote: > On Wed, 19 Jun 2019 09:28:42 -0700 Yang Shi wrote: > >>> Sorry for replying rather late, and not in the v2 thread, but unlike >>> Hugh I'm not convinced that we should include vma size/alignment in the >>> test for reporting THPeligible, which was supposed to reflect >>> administrative settings and madvise hints. I guess it's mostly a matter >>> of personal feeling. But one objective distinction is that the admin >>> settings and madvise do have an exact binary result for the whole VMA, >>> while this check is more fuzzy - only part of the VMA's span might be >>> properly sized+aligned, and THPeligible will be 1 for the whole VMA. >> >> I think THPeligible is used to tell us if the vma is suitable for >> allocating THP. Both anonymous and shmem THP checks vma size/alignment >> to decide to or not to allocate THP. >> >> And, if vma size/alignment is not checked, THPeligible may show "true" >> for even 4K mapping. This doesn't make too much sense either. > > This discussion seems rather inconclusive. I'll merge up the patchset > anyway. Vlastimil, if you think some changes are needed here then > please let's get them sorted out over the next few weeks? Well, Hugh did ack it, albeit without commenting on this part. I don't feel strongly enough about this for a nack.