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s=arc-20220608; d=hostedemail.com; t=1725464423; a=rsa-sha256; cv=none; b=F/chTmO2QduXuSFmGy4wfSFTFNqrdgRLwrlnZ1no5jVDmEhsnJhkC5K25qx2Q5aOeal7PK ojui2kCauNjkrOPiaNdMuSLRGf0z6CcsMMptli1g6/DWm8uESgHfCUXhY+R6pTg7T3V6j0 V25dC5SVjCSpd4naHQpNqRQxkZe+vrk= ARC-Authentication-Results: i=1; imf30.hostedemail.com; dkim=none; dmarc=pass (policy=none) header.from=arm.com; spf=pass (imf30.hostedemail.com: domain of dev.jain@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=dev.jain@arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 7865BFEC; Wed, 4 Sep 2024 08:42:35 -0700 (PDT) Received: from [10.163.62.239] (unknown [10.163.62.239]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 72F283F73F; Wed, 4 Sep 2024 08:42:00 -0700 (PDT) Message-ID: <98f73b2f-ec1c-4e81-bfb2-6e02ebc4cdae@arm.com> Date: Wed, 4 Sep 2024 21:11:57 +0530 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 0/2] Do not shatter hugezeropage on wp-fault To: Ryan Roberts , akpm@linux-foundation.org, david@redhat.com, willy@infradead.org, kirill.shutemov@linux.intel.com Cc: anshuman.khandual@arm.com, catalin.marinas@arm.com, cl@gentwo.org, vbabka@suse.cz, mhocko@suse.com, apopple@nvidia.com, dave.hansen@linux.intel.com, will@kernel.org, baohua@kernel.org, jack@suse.cz, mark.rutland@arm.com, hughd@google.com, aneesh.kumar@kernel.org, yang@os.amperecomputing.com, peterx@redhat.com, ioworker0@gmail.com, jglisse@google.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <20240904100923.290042-1-dev.jain@arm.com> <2427338d-7be5-4939-8d01-6d99b9167fea@arm.com> Content-Language: en-US From: Dev Jain In-Reply-To: <2427338d-7be5-4939-8d01-6d99b9167fea@arm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 6446880010 X-Stat-Signature: fr89z4scuh3zmdqx5puxwb8jzaozg65h X-Rspam-User: X-HE-Tag: 1725464530-260670 X-HE-Meta: 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 dBdoP9ia wX73xKAUPQIYyNRTcjtk8shLb0pxBlSLt1/CcZoWEOZnlKzkrLlke67PNRHB5VEt2IThXec9AfPY2RH661+I4yktejj8qhIb7MA0W7zv5GRWX6rqDYNKnO+Q5JlrfWu34Ry0lv6+kOe3FBmnDZzPfNGxnOlehIT1owUQPSn7D098IXrQOc0Hlh+x8yc4cAcci7L3Lbz6zyRY76qTwjOtYIRVnQgUugrGL3fJZ 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 9/4/24 17:06, Ryan Roberts wrote: > Hi Dev, > > On 04/09/2024 11:09, Dev Jain wrote: >> It was observed at [1] and [2] that the current kernel behaviour of >> shattering a hugezeropage is inconsistent and suboptimal. For a VMA with >> a THP allowable order, when we write-fault on it, the kernel installs a >> PMD-mapped THP. On the other hand, if we first get a read fault, we get >> a PMD pointing to the hugezeropage; subsequent write will trigger a >> write-protection fault, shattering the hugezeropage into one writable >> page, and all the other PTEs write-protected. The conclusion being, as >> compared to the case of a single write-fault, applications have to suffer >> 512 extra page faults if they were to use the VMA as such, plus we get >> the overhead of khugepaged trying to replace that area with a THP anyway. >> >> Instead, replace the hugezeropage with a THP on wp-fault. >> >> v1->v2: >> - Wrap do_huge_zero_wp_pmd_locked() around lock and unlock >> - Call thp_fault_alloc() before do_huge_zero_wp_pmd_locked() to avoid >> - calling sleeping function from spinlock context >> >> [1]: https://lore.kernel.org/all/3743d7e1-0b79-4eaf-82d5-d1ca29fe347d@arm.com/ >> [2]: https://lore.kernel.org/all/1cfae0c0-96a2-4308-9c62-f7a640520242@arm.com/ >> >> Dev Jain (2): >> mm: Abstract THP allocation >> mm: Allocate THP on hugezeropage wp-fault >> >> include/linux/huge_mm.h | 6 ++ >> mm/huge_memory.c | 171 +++++++++++++++++++++++++++++----------- >> mm/memory.c | 5 +- >> 3 files changed, 136 insertions(+), 46 deletions(-) >> > What is the base for this? It doesn't apply on top of mm-unstable. Sorry, forgot to mention, it applies on v6.11-rc5. > > Thanks, > Ryan >