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[2003:cb:c708:8a00:362b:7e34:a3bc:9ddf]) by smtp.gmail.com with ESMTPSA id g8-20020a05600c310800b0041488cfd0fesm2696526wmo.28.2024.03.27.10.02.29 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 27 Mar 2024 10:02:30 -0700 (PDT) Message-ID: <6076ac95-b6c6-464c-8af0-6d5ab2d1a331@redhat.com> Date: Wed, 27 Mar 2024 18:02:29 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH v1 1/4] mm: Introduce ptep_get_lockless_norecency() To: Ryan Roberts , Mark Rutland , Catalin Marinas , Will Deacon , Alexander Shishkin , Jiri Olsa , Ian Rogers , Adrian Hunter , Andrew Morton , Muchun Song Cc: linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20240215121756.2734131-1-ryan.roberts@arm.com> <20240215121756.2734131-2-ryan.roberts@arm.com> <7aefa967-43aa-490b-ae0d-7d1455402e89@redhat.com> <5c8dbda1-5b89-4599-9bc2-f840e7bc6a74@arm.com> <6777213f-6273-4942-86be-e712ee5ebd1a@redhat.com> <31b903f8-99dd-4790-8338-f4b9950b1ee6@arm.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 293951C004A X-Rspam-User: X-Rspamd-Server: rspam02 X-Stat-Signature: o4uca8tni1o8tuzino3a6autbkjs71yw X-HE-Tag: 1711558954-196438 X-HE-Meta: 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 9B8voCdW /hD3WI5pWpX7SoJi49/lHWWPbBRnrZ5kFMgfufrUavSWr4ZD4qF5ikbT9CK5UOnn0iMhTgJincrk8pgufxQPUq+Amh4Wixey+C7OiQPwUoK+BnUJ8fRPPnNld0ii1BopkI3JFFcNz2SPVfLwv03hpLLYeP7qLHjGMBrV3geDAsJh2hxa7gh3ZUg6WkwF7jX9erXwozjbaRyf+gSq2RDJu8Ruv5yO4Pzz/vCJQ60AFYdK1YlkO3bBApmXHVDpo/1szkjGN/7lS28ORG1ucUVj9CA91bYuN8pWoxXBcxyWBuuI2DZ9L60iBundcaQu9c+uXVOsXwe/ZSX5d0cJv1g1dwdU1AaMJ7kCdFMG4sovr7cAiuUQS3/EvpX0sb5R/lnqyRZOhZ6hevgb19rLyy8TuPb44gA4C2bPCUaL1FJEFEqcdHI6SCf53FJBOjAbUbktRcoqMh2wuEU80ov/FnLWaRD/Btg== 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: >>>> >>>>> diff --git a/mm/hugetlb.c b/mm/hugetlb.c >>>>> index 68283e54c899..41dc44eb8454 100644 >>>>> --- a/mm/hugetlb.c >>>>> +++ b/mm/hugetlb.c >>>>> @@ -7517,7 +7517,7 @@ pte_t *huge_pte_alloc(struct mm_struct *mm, struct >>>>> vm_area_struct *vma, >>>>>        } >>>>> >>>>>        if (pte) { >>>>> -        pte_t pteval = ptep_get_lockless(pte); >>>>> +        pte_t pteval = ptep_get_lockless_norecency(pte); >>>>> >>>>>            BUG_ON(pte_present(pteval) && !pte_huge(pteval)); >>>>>        } >>>>> diff --git a/mm/khugepaged.c b/mm/khugepaged.c >>>>> index 2771fc043b3b..1a6c9ed8237a 100644 >>>>> --- a/mm/khugepaged.c >>>>> +++ b/mm/khugepaged.c >>>>> @@ -1019,7 +1019,7 @@ static int __collapse_huge_page_swapin(struct mm_struct >>>>> *mm, >>>>>                } >>>>>            } >>>>> >>>>> -        vmf.orig_pte = ptep_get_lockless(pte); >>>>> +        vmf.orig_pte = ptep_get_lockless_norecency(pte); >>>>>            if (!is_swap_pte(vmf.orig_pte)) >>>>>                continue; >>>> >>>> >>>> Hm, I think you mentioned that we want to be careful with vmf.orig_pte. >>> >>> Yeah good point. So I guess this should move to patch 3 (which may be dropped - >>> tbd)? >>> >> >> Yes. Or a separate one where you explain in detail why do_swap_page() can handle >> it just fine. > > Ahh no wait - I remember now; the reason I believe this is a "trivial" case is > because we only leak vmf.orig_pte to the rest of the world if its a swap entry. Ugh, yes! -- Cheers, David / dhildenb