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[2003:cb:c715:6600:a077:c7da:3362:6896]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-432dac0ae3asm32070715e9.27.2024.11.14.13.19.01 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 14 Nov 2024 13:19:02 -0800 (PST) Message-ID: Date: Thu, 14 Nov 2024 22:19:00 +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 13:51, Qi Zheng wrote: > > > On 2024/11/14 20:32, David Hildenbrand wrote: >> 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. > > Yes. > >> >> Can't you simply return the number of pte_none that you skipped here >> using another >> input variable, if really required? > > Suppose we add an input variable nr_skip to do_zap_pte_range(), you mean > to return the above nr to zap_pte_range() through: Maybe "cur_none_nr" or something similar. > > *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 pte_none though (to digest why it is required :) ). -- Cheers, David / dhildenb