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[2003:cb:c715:6600:a077:c7da:3362:6896]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-432dab80582sm19043785e9.19.2024.11.14.04.32.22 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 14 Nov 2024 04:32:23 -0800 (PST) Message-ID: Date: Thu, 14 Nov 2024 13:32:21 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 14.11.24 10:20, Qi Zheng wrote: > > > On 2024/11/14 16:04, David Hildenbrand wrote: >> >>>   static unsigned long zap_pte_range(struct mmu_gather *tlb, >>>                   struct vm_area_struct *vma, pmd_t *pmd, >>>                   unsigned long addr, unsigned long end, >>> @@ -1682,13 +1704,17 @@ static unsigned long zap_pte_range(struct >>> mmu_gather *tlb, >>>           pte_t ptent = ptep_get(pte); >>>           int max_nr; >>> -        nr = 1; >>> -        if (pte_none(ptent)) >>> -            continue; >>> - >>>           if (need_resched()) >>>               break; >>> +        nr = skip_none_ptes(pte, addr, end); >>> +        if (nr) { >>> +            addr += PAGE_SIZE * nr; >>> +            if (addr == end) >>> +                break; >>> +            pte += nr; >>> +        } >>> + >>>           max_nr = (end - addr) / PAGE_SIZE; >> >> I dislike calculating max_nr twice, once here and once in skip_non_ptes. >> >> Further, you're missing to update ptent here. > > Oh, my bad. However, with [PATCH v3 5/9], there will be no problem, but > there are still two ptep_get() and max_nr calculation. > > If you inline it you can >> avoid another ptep_get(). > > Do you mean to inline the skip_none_ptes() into do_zap_pte_range()? Effectively moving this patch after #5, and have it be something like: diff --git a/mm/memory.c b/mm/memory.c index 1949f5e0fece5..4f5d1e4c6688e 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -1667,8 +1667,21 @@ static inline int do_zap_pte_range(struct mmu_gather *tlb, pte_t ptent = ptep_get(pte); int max_nr = (end - addr) / PAGE_SIZE; - if (pte_none(ptent)) - return 1; + /* Skip all consecutive pte_none(). */ + if (pte_none(ptent)) { + int nr; + + for (nr = 1; nr < max_nr; nr++) { + ptent = ptep_get(pte + nr); + if (!pte_none(ptent)) + break; + } + max_nr -= nr; + if (!max_nr) + return nr; + pte += nr; + addr += nr * PAGE_SIZE; + } if (pte_present(ptent)) return zap_present_ptes(tlb, vma, pte, ptent, max_nr, In the context of this patch this makes most sense. Regarding "count_pte_none" comment, I assume you talk about patch #7. Can't you simply return the number of pte_none that you skipped here using another input variable, if really required? -- Cheers, David / dhildenb