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s=arc-20220608; d=hostedemail.com; t=1736489505; a=rsa-sha256; cv=none; b=gLUVq2AngZdrVnrMfwKuVZzFM+QtPm3vgLq7St6jDZTIzCCXebAVOQ0Kd/2riyF7nbuPNu Ie8efmS5yTSnvE73iMNZwd+xdBCkyMoptHj1HFHAmcV0805VIAnTxhjNv6FiicQPFogv0P H7F+fBZdK50R332RJwMY7OXdbkrnb/I= ARC-Authentication-Results: i=1; imf20.hostedemail.com; dkim=none; dmarc=pass (policy=none) header.from=arm.com; spf=pass (imf20.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 0EC811477; Thu, 9 Jan 2025 22:12:12 -0800 (PST) Received: from [10.162.42.21] (K4MQJ0H1H2.blr.arm.com [10.162.42.21]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id B85963F673; Thu, 9 Jan 2025 22:11:31 -0800 (PST) Message-ID: <3a1af9a6-451d-46ec-804f-cdb5d3d21f41@arm.com> Date: Fri, 10 Jan 2025 11:41:28 +0530 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC 03/11] khugepaged: Don't allocate khugepaged mm_slot early To: Nico Pache , linux-kernel@vger.kernel.org, linux-mm@kvack.org Cc: ryan.roberts@arm.com, 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, srivatsa@csail.mit.edu, haowenchao22@gmail.com, hughd@google.com, aneesh.kumar@kernel.org, yang@os.amperecomputing.com, peterx@redhat.com, ioworker0@gmail.com, wangkefeng.wang@huawei.com, ziy@nvidia.com, jglisse@google.com, surenb@google.com, vishal.moola@gmail.com, zokeefe@google.com, zhengqi.arch@bytedance.com, jhubbard@nvidia.com, 21cnbao@gmail.com, willy@infradead.org, kirill.shutemov@linux.intel.com, david@redhat.com, aarcange@redhat.com, raquini@redhat.com, sunnanyong@huawei.com, usamaarif642@gmail.com, audra@redhat.com, akpm@linux-foundation.org References: <20250108233128.14484-1-npache@redhat.com> <20250108233128.14484-4-npache@redhat.com> Content-Language: en-US From: Dev Jain In-Reply-To: <20250108233128.14484-4-npache@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: DAD901C0007 X-Rspam-User: X-Rspamd-Server: rspam07 X-Stat-Signature: trgmi7nuzu7rpmq7h9u31peyhyt66w8z X-HE-Tag: 1736489504-551565 X-HE-Meta: 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 9GHLpzFj aThInu0AaguNIq/L6k5H3c3rZv6fol7D8tMiofIzpPxILXx6rg+xlKQcez8luo5dN4Hmdfo6pk1c8FSRr9LwbNzgahhKM6tH6jiVrpyLPRCWNS/6zqYIkg4ax03SsQbFEcIvSo5FiwaL1yHtIqJgSsQOTFut41m/Ru6OMo7hLdEw8vJti7iER7UQmAkH8s7d3uW9FoC4pF0dvsGREFiAuTN+1K1zkwf/vGFXwfygmERpJ0taZ5kOwgZFkMv/T8yvtv0l9B5IqBj0F2r6s4ejVr2DXuo3tqlHUqEna 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 09/01/25 5:01 am, Nico Pache wrote: > We should only "enter"/allocate the khugepaged mm_slot if we succeed at > allocating the PMD sized folio. Move the khugepaged_enter_vma call until > after we know the vma_alloc_folio was successful. Why? We have the appropriate checks from thp_vma_allowable_orders() and friends, so the VMA should be registered with khugepaged irrespective of whether during fault time we are able to allocate a PMD-THP or not. If we fail at fault time, it is the job of khugepaged to try to collapse it later. > > Signed-off-by: Nico Pache > --- > mm/huge_memory.c | 3 +-- > 1 file changed, 1 insertion(+), 2 deletions(-) > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index e53d83b3e5cf..635c65e7ef63 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -1323,7 +1323,6 @@ vm_fault_t do_huge_pmd_anonymous_page(struct vm_fault *vmf) > ret = vmf_anon_prepare(vmf); > if (ret) > return ret; > - khugepaged_enter_vma(vma, vma->vm_flags); > > if (!(vmf->flags & FAULT_FLAG_WRITE) && > !mm_forbids_zeropage(vma->vm_mm) && > @@ -1365,7 +1364,7 @@ vm_fault_t do_huge_pmd_anonymous_page(struct vm_fault *vmf) > } > return ret; > } > - > + khugepaged_enter_vma(vma, vma->vm_flags); > return __do_huge_pmd_anonymous_page(vmf); > } > In any case, you are not achieving what you described in the patch description: you have moved khugepaged_enter_vma() after the read fault logic, what you want to do is to move it after vma_alloc_anon_folio_pmd() in __do_huge_pmd_anonymous_page().