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[2003:cb:c721:8100:177e:1983:5478:64ec]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-432dab721d7sm57786805e9.9.2024.11.15.07.00.00 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 15 Nov 2024 07:00:01 -0800 (PST) Message-ID: <4edccc1a-2761-4a5a-89a6-7869c1b6b08a@redhat.com> Date: Fri, 15 Nov 2024 15:59:59 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 4/9] mm: introduce skip_none_ptes() To: Qi Zheng Cc: jannh@google.com, hughd@google.com, willy@infradead.org, muchun.song@linux.dev, vbabka@kernel.org, akpm@linux-foundation.org, peterx@redhat.com, mgorman@suse.de, catalin.marinas@arm.com, will@kernel.org, dave.hansen@linux.intel.com, luto@kernel.org, peterz@infradead.org, x86@kernel.org, lorenzo.stoakes@oracle.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, zokeefe@google.com, rientjes@google.com References: <574bc9b646c87d878a5048edb63698a1f8483e10.1731566457.git.zhengqi.arch@bytedance.com> <617a063e-bd84-4da5-acf4-6ff516512055@bytedance.com> <253e5fd0-7e98-43fd-b0d7-8a5b739ae4aa@bytedance.com> <77b1eddf-7c1b-43e9-9352-229998ce3fc7@redhat.com> <5a3428bd-743a-4d51-8b75-163ab560bca7@bytedance.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: C2EC21A002B X-Stat-Signature: 57q3fk7sm45rymijkabctqygjenouh7w X-HE-Tag: 1731682749-106011 X-HE-Meta: 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 LeumMlf3 K6uCuEH9kiG0m/pxs5/Oc98s/Us6Pw1pSLhRmvn2+o1AbzHu3lG1CPtSg8QKXNYzqVFzr3Z/iyUDxYSoLU8jCR0Ii3bXoaWlc1PKMOpxP7I98AHaFiPDl+satiIAlxZee3Sue4w35D7AtpXdUM5KbYhHVmd9gRUk2LvbC/hmWdahkCahJYkoi+kdJuML7fPinyN5H2InuPY6VytIjodR2MHT5ERTF/bL6Acs2uUtRIfrkKztnjTAi3WlIzqP3322vl3dSAznuPkE7UBXtoIcTakNlUDkHw9BXwKpMdRhEOIXaDMvIyZ3akJy5kC2PY7QtpveXuu9KzNqpHvreCUg4ul+ooiaO65vNx5Z632o5a0RmKTbp/A13qLGyBsaCHWHfiPBJrTDuxm3RqA+Yc45E6FIGa5tIYDfMyc554TRjnLz21TixwOpEFlYIzzQkyVwSi4plN2RzVBp44pbtp0dNGhtbIQ== 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 15.11.24 15:41, Qi Zheng wrote: > > > On 2024/11/15 18:22, David Hildenbrand wrote: >>>>> *nr_skip = nr; >>>>> >>>>> and then: >>>>> >>>>> zap_pte_range >>>>> --> nr = do_zap_pte_range(tlb, vma, pte, addr, end, details, &skip_nr, >>>>>                           rss, &force_flush, &force_break); >>>>>        if (can_reclaim_pt) { >>>>>            none_nr += count_pte_none(pte, nr); >>>>>            none_nr += nr_skip; >>>>>        } >>>>> >>>>> Right? >>>> >>>> Yes. I did not look closely at the patch that adds the counting of >>> >>> Got it. >>> >>>> pte_none though (to digest why it is required :) ). >>> >>> Because 'none_nr == PTRS_PER_PTE' is used in patch #7 to detect >>> empty PTE page. >> >> Okay, so the problem is that "nr" would be "all processed entries" but >> there are cases where we "process an entry but not zap it". >> >> What you really only want to know is "was any entry not zapped", which >> could be a simple input boolean variable passed into do_zap_pte_range? >> >> Because as soon as any entry was processed but  no zapped, you can >> immediately give up on reclaiming that table. > > Yes, we can set can_reclaim_pt to false when a !pte_none() entry is > found in count_pte_none(). I'm not sure if well need cont_pte_none(), but I'll have to take a look at your new patch to see how this fits together with doing the pte_none detection+skipping in do_zap_pte_range(). I was wondering if you cannot simply avoid the additional scanning and simply set "can_reclaim_pt" if you skip a zap. -- Cheers, David / dhildenb