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[2003:cb:c72f:6100:aae:4b84:887c:15bb]) by smtp.gmail.com with ESMTPSA id bn23-20020a170906c0d700b00a462e4d7216sm786317ejb.76.2024.03.11.09.19.27 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 11 Mar 2024 09:19:27 -0700 (PDT) Message-ID: Date: Mon, 11 Mar 2024 17:19:26 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/1] mm/khugepaged: reduce process visible downtime by pre-zeroing hugepage To: Lance Yang , akpm@linux-foundation.org Cc: mhocko@suse.com, zokeefe@google.com, shy828301@gmail.com, xiehuan09@gmail.com, songmuchun@bytedance.com, minchan@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20240308074921.45752-1-ioworker0@gmail.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63XOwU0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAHCwXwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat In-Reply-To: <20240308074921.45752-1-ioworker0@gmail.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 3C42140008 X-Rspam-User: X-Stat-Signature: 1qrqw8ezmi8bfrudd94dduy9ecem3kai X-Rspamd-Server: rspam03 X-HE-Tag: 1710173978-354918 X-HE-Meta: U2FsdGVkX18GQ7bsn7CBXHH20juSIGqMowmZd0e7MnMK8bnuUKrBa8ypkwsWWHPECuYdsytvhwkUIPewf5/Oa8VoS0jxP1b/jhyXS7zCRT1VQ8OI66+4PwcLi5BmrG0wyc772pvRe98nSZkgcZfuhzlTAP2dCNnPWhq9iYWBAhy3YVDetScXXN5RVaYvAWG8L9X3FXnMqgxCNKyc+gwdS1RyFISJns9/S+i9wimGhRlFSOQzqfZ3L5pUJFON7+FPFkpdNHXEY411sn7C2EzpIYWmwYs3EuMtQDFiwJAOHG0iEyhilJoJQsLIas/AR/KakLxto4BS4mdJRLVqJGd4ANsf6H0y1QuLOJ1vbLobyW4fr0SbSmckBGKO63SyFnPGnuKa3md65R1unpjvh7aXwYoLgOTeEuD0NeKlOsy4cKI6I9a7WBdLjmw2C1asmiuEHSFAbEXQ3yTjCbvcGjFSBo/Q09cbPV5/xhOFJOFMXrBFsxTLFPn10YeY9N7APLAkVcLIoHTOkH6VaBxXrG1C6qEpcOm0t5+5nEZcnS28ngwh8/56vLhve5bSbDxvou4B4b7LAwSK7kuFCsvBqtzd4TAG2ZCrfZrjSB8JWvexjFiTT+m+2OYdmlEIWZaDzcxBslsy2dCs3LAMTpnn2GMRR+CYzAhq4xWKm1xDcXbE6PKZUig/me0sdSwBqILiAEl6vo3RTf5wIbVu7m3ZNkNOTGitHCUw0xX3YCarRAJKEPN2Lm3D1Nuvvx+tIAIFjRzMh++E/BNvIw/2YS7FbV+vrA1n8wA2whnMhhUWeAdtf6bd4L0PreHXg3KiLbVcd4nLoGVckW7SkbALN6w3YTof+Hlniq5HFN1T4dU6D4FfRGI0Tc4xMSLb172VPGTFKo3Xlm6bCmKI1uYL/w60LyBq9SsP3lNPccwVycKyF2bpWX4uE+ce2bdDgfnls/E1SpWkVYsd9lXktNt1awu2MmD XL+S5S/8 hpxpGFLJm+A95g2qm+wCDZA+YuSrFl2Yp+JT9ydWEPpr5k/OSpgLGlHiZ2w5khsXUkxczP4diezkP1C5eaUg3m2iOOSaGpkzVPcrHPp2O0ze3/Ad3UBjXK/cLWeJufctS2xMbIawNkb53eYOC4Ti4dkI9xKld8edpCDuAL89BllindQZLg6vBIQQ/NIy4nIX7vHOeL/oah91xC4+l2bRpSSM0tyAZ4+LHQina2XgUSIR7kvMx+Uxdh+KiIm4VL3fxZnOCmEHDUynwQHTciXA5LBY45d3C4xuSqjnSaSZaTnYhJX16tqnenoYp9HE9Es6kE8nBytDpu1QiIQGto6GmwX0VqhVqoWczmL7RzvH9wzc4XpOcEEiJ1a/aChfMS3/LRzNVOvK1vRVgwpSBxSxNksNUbvPxQxc2I7HLAxiFsH6Yq7YM3jNzDATPTOMO+V8X34S418e+ty3gMiU3TDyLtf9EyFY0YZAl9ooP 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: List-Subscribe: List-Unsubscribe: On 08.03.24 08:49, Lance Yang wrote: > The patch reduces the process visible downtime during hugepage > collapse. This is achieved by pre-zeroing the hugepage before > acquiring mmap_lock(write mode) if nr_pte_none >= 256, without > affecting the efficiency of khugepaged. > > On an Intel Core i5 CPU, the process visible downtime during > hugepage collapse is as follows: > > | nr_ptes_none | w/o __GFP_ZERO | w/ __GFP_ZERO | Change | > --------------------------------------------------—---------- > | 511 | 233us | 95us | -59.21%| > | 384 | 376us | 219us | -41.20%| > | 256 | 421us | 323us | -23.28%| > | 128 | 523us | 507us | -3.06%| > > Of course, alloc_charge_hpage() will take longer to run with > the __GFP_ZERO flag. > > | Func | w/o __GFP_ZERO | w/ __GFP_ZERO | > |----------------------|----------------|---------------| > | alloc_charge_hpage | 198us | 295us | > > But it's not a big deal because it doesn't impact the total > time spent by khugepaged in collapsing a hugepage. In fact, > it would decrease. It does look sane to me and not overly complicated. But, it's an optimization really only when we have quite a bunch of pte_none(), possibly repeatedly so that it really makes a difference. Usually, when we repeatedly collapse that many pte_none() we're just wasting a lot of memory and should re-evaluate life choices :) So my question is: do we really care about it that much that we care to optimize? But again, LGTM. -- Cheers, David / dhildenb