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[2003:cb:c735:400:2501:5a2e:13c6:88da]) by smtp.gmail.com with ESMTPSA id 25-20020a05600c025900b003fc00702f65sm8323118wmj.46.2023.07.17.09.48.58 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 17 Jul 2023 09:48:59 -0700 (PDT) Message-ID: <0250a2d7-c79b-0e0f-8161-bf475daf1c82@redhat.com> Date: Mon, 17 Jul 2023 18:48:57 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.12.0 Subject: Re: [PATCH v1 1/3] mm: Allow deferred splitting of arbitrary large anon folios Content-Language: en-US To: Ryan Roberts , Andrew Morton , Matthew Wilcox , Yin Fengwei , Yu Zhao , Yang Shi , "Huang, Ying" , Zi Yan Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <20230717143110.260162-1-ryan.roberts@arm.com> <20230717143110.260162-2-ryan.roberts@arm.com> <90b406af-9db4-b668-a7a0-e574e104c84c@redhat.com> <028c5f5b-b67c-9ccc-bc06-468f47362999@arm.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: <028c5f5b-b67c-9ccc-bc06-468f47362999@arm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 17.07.23 18:01, Ryan Roberts wrote: > On 17/07/2023 16:42, David Hildenbrand wrote: >> On 17.07.23 16:31, Ryan Roberts wrote: >>> In preparation for the introduction of large folios for anonymous >>> memory, we would like to be able to split them when they have unmapped >>> subpages, in order to free those unused pages under memory pressure. So >>> remove the artificial requirement that the large folio needed to be at >>> least PMD-sized. >>> >>> Signed-off-by: Ryan Roberts >>> Reviewed-by: Yu Zhao >>> Reviewed-by: Yin Fengwei >>> --- >>>   mm/rmap.c | 2 +- >>>   1 file changed, 1 insertion(+), 1 deletion(-) >>> >>> diff --git a/mm/rmap.c b/mm/rmap.c >>> index 0c0d8857dfce..2baf57d65c23 100644 >>> --- a/mm/rmap.c >>> +++ b/mm/rmap.c >>> @@ -1430,7 +1430,7 @@ void page_remove_rmap(struct page *page, struct >>> vm_area_struct *vma, >>>            * page of the folio is unmapped and at least one page >>>            * is still mapped. >>>            */ >>> -        if (folio_test_pmd_mappable(folio) && folio_test_anon(folio)) >>> +        if (folio_test_large(folio) && folio_test_anon(folio)) >>>               if (!compound || nr < nr_pmdmapped) >>>                   deferred_split_folio(folio); >> >> !compound will always be true I guess, so nr_pmdmapped == 0 (which will always >> be the case) will be ignored. > > I don't follow why !compound will always be true. This function is > page_remove_rmap() (not folio_remove_rmap_range() which I add in a later patch). > page_remove_rmap() can work on pmd-mapped pages where compound=true is passed in. I was talking about the folio_test_pmd_mappable() -> folio_test_large() change. For folio_test_large() && !folio_test_pmd_mappable() I expect that we'll never pass in "compound=true". -- Cheers, David / dhildenb