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[2003:d8:2f20:da00:b70a:d502:3b51:1f2d]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3e7607cd691sm6839560f8f.32.2025.09.12.06.47.58 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 12 Sep 2025 06:48:00 -0700 (PDT) Message-ID: <43f42d9d-f814-4b54-91a6-3073f7c7cedf@redhat.com> Date: Fri, 12 Sep 2025 15:47:58 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v11 00/15] khugepaged: mTHP support To: Kiryl Shutsemau , Nico Pache Cc: linux-mm@kvack.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, ziy@nvidia.com, baolin.wang@linux.alibaba.com, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, ryan.roberts@arm.com, dev.jain@arm.com, corbet@lwn.net, rostedt@goodmis.org, mhiramat@kernel.org, mathieu.desnoyers@efficios.com, akpm@linux-foundation.org, baohua@kernel.org, willy@infradead.org, peterx@redhat.com, wangkefeng.wang@huawei.com, usamaarif642@gmail.com, sunnanyong@huawei.com, vishal.moola@gmail.com, thomas.hellstrom@linux.intel.com, yang@os.amperecomputing.com, aarcange@redhat.com, raquini@redhat.com, anshuman.khandual@arm.com, catalin.marinas@arm.com, tiwai@suse.de, will@kernel.org, dave.hansen@linux.intel.com, jack@suse.cz, cl@gentwo.org, jglisse@google.com, surenb@google.com, zokeefe@google.com, hannes@cmpxchg.org, rientjes@google.com, mhocko@suse.com, rdunlap@infradead.org, hughd@google.com, richard.weiyang@gmail.com, lance.yang@linux.dev, vbabka@suse.cz, rppt@kernel.org, jannh@google.com, pfalcato@suse.de References: <20250912032810.197475-1-npache@redhat.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 445BD160012 X-Stat-Signature: xqexsd6kwwxziqjrxg7n3jccntantwwx X-HE-Tag: 1757684886-437754 X-HE-Meta: U2FsdGVkX1+rv641MQNr5fCToSk7Vx0HukJn/8RhKhZf1x56QVTTWQzF0zEs790hlZpKqRJrjuU6+zOKllhyGv1zWHXXrr7mlg3TaCKB2Zu3ydPUp9NH9jdYU1Kd1Fm+giT+yucOc7+RdrTyWb+Vt806ZSJgDBhin0GJCEs0xHOBu2Ch3IXsGmj1FhPeOipR12FbrquRq2S98Ngq3LcIp432+aUhGGQ7zvy9rXz07NtPzBbFZ9d2O1pwPxaDMrBb24vPuntM3TOS+X74Pw3Uj49Vc9lxT+SOQPwxGssglSGOYy5kNTzUa5do33kqWOdHC+pDfCgVD1HeM+Yt8rqNgbIUx/ZLeHozDxhjjLMu5QTndPnjfi3tULrlUtarZwtc/cO01VvWDKIQauiUMbP3WkurlQnsWJupdZ3Xvh5+kZgdWk89OY8b5dbvoXDiTz6bBnLJgoVjzd86FNPb+wU2egxtRdx1/eoLof44qyNThZvJ86jeSgr/XLOm5PUb9zxLGlFYB03gksrGKoCZ0Kil0i8udKBgGfIKkaw1uVW1EWffzQYdcLWi90Er/Iesr1PtKpN1eOhQsV2SKeAZ4YTpLf2UtZttwWuViPp6ao4Xvse2QENRzIm8lUUAwOJcfsT9Ad8jyssV4zTsSbFYwsSYnleDXkaTY01gCOXsAGOM9swWk1dDsg34xWAYRcdZbs8MVkIOXVi83CGc1yuDN0wjocsZkPQyZNlYJs73o39jEkq2nXPed8kPJ/2Hsj49MiaNOPWI266VN2xlXavgExpm9/+DvEq3b347QT+jVc1ueUz9TdR98w0kOsFKfyp1Hod/RkF7ThwjoSKyOCgGhTQJqroWZHSWbtLfGxIPMFcHLhlPexvHCSC4mlo+WnrBW2Z2DLyqUuRGfdDFFADfaIpfQKbXKlocc3hqzswsepxbU+3irXQrRbn4AUqs4JQPXfMN8Od0g8ua11m6ei3zuZm KqwvgrV5 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 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 12.09.25 14:19, Kiryl Shutsemau wrote: > On Thu, Sep 11, 2025 at 09:27:55PM -0600, Nico Pache wrote: >> The following series provides khugepaged with the capability to collapse >> anonymous memory regions to mTHPs. >> >> To achieve this we generalize the khugepaged functions to no longer depend >> on PMD_ORDER. Then during the PMD scan, we use a bitmap to track individual >> pages that are occupied (!none/zero). After the PMD scan is done, we do >> binary recursion on the bitmap to find the optimal mTHP sizes for the PMD >> range. The restriction on max_ptes_none is removed during the scan, to make >> sure we account for the whole PMD range. When no mTHP size is enabled, the >> legacy behavior of khugepaged is maintained. max_ptes_none will be scaled >> by the attempted collapse order to determine how full a mTHP must be to be >> eligible for the collapse to occur. If a mTHP collapse is attempted, but >> contains swapped out, or shared pages, we don't perform the collapse. It is >> now also possible to collapse to mTHPs without requiring the PMD THP size >> to be enabled. >> >> When enabling (m)THP sizes, if max_ptes_none >= HPAGE_PMD_NR/2 (255 on >> 4K page size), it will be automatically capped to HPAGE_PMD_NR/2 - 1 for >> mTHP collapses to prevent collapse "creep" behavior. This prevents >> constantly promoting mTHPs to the next available size, which would occur >> because a collapse introduces more non-zero pages that would satisfy the >> promotion condition on subsequent scans. > > Hm. Maybe instead of capping at HPAGE_PMD_NR/2 - 1 we can count > all-zeros 4k as none_or_zero? It mirrors the logic of shrinker. BTW, I thought further about this and I agree: if we count zero-filled pages towards none_or_zero one we can avoid the "creep" problem. The scanning-for-zero part is rather nasty, though. -- Cheers David / dhildenb