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[2003:d8:2f16:1800:a9b4:1776:c5d9:1d9a]) by smtp.gmail.com with ESMTPSA id h20-20020a05600c351400b003dc1300eab0sm17270274wmq.33.2023.01.30.01.34.04 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 30 Jan 2023 01:34:04 -0800 (PST) Message-ID: Date: Mon, 30 Jan 2023 10:34:03 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.6.0 Subject: Re: [PATCH mm-unstable v2 1/6] mm: Add folio_estimated_mapcount() To: Jane Chu , Vishal Moola Cc: linux-mm@kvack.org, akpm@linux-foundation.org, linux-kernel@vger.kernel.org References: <20230124012210.13963-1-vishal.moola@gmail.com> <20230124012210.13963-2-vishal.moola@gmail.com> <477bbc1e-a60a-cfce-d31e-0b4bdd5f6429@redhat.com> <526e5156-6c4b-9f2c-1637-2f83c1dfea1e@redhat.com> <53d86764-d155-8d97-1a4d-7e701848c950@redhat.com> <52af321f-175b-9fa9-10f0-ac2bba04c677@redhat.com> <3a6af06a-729d-7659-50b0-8b242b555134@oracle.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: <3a6af06a-729d-7659-50b0-8b242b555134@oracle.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 9CF664000F X-Stat-Signature: rzrg1w86apkheccsmd5363snh6qx7zbh X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1675071248-851039 X-HE-Meta: U2FsdGVkX1/xNgco4RZhlXybrC9ARewq1cwBFvDyfY2iNx7EaOU0oGXmsrJtqbOvPu7zqVBhh7/0p9VJNYRmnZPU83AJ5unpI31tTMRCy43Qy3W/PwjxjDQPpbaP2EmmXG/fhoeuZqIV03puEq0PpdWFH6dCZdufaQvoHaokp2dlyjKE+dEOtoTlhgxG48uEn4KRhGFRmnKYNsxnTjSSBlpkB/r5Xanmxn7pLYf1q02dleiHtiLR42OG9wc6sMGiQ8cXNHPCgMgfVlP4Exy9EDC/7iFIa8qm0U4MrsXETQp8q0MFeZ1BdGgY1RQSPcHI3TMbwMIWKeYGTbFMKnf6kusKvfnK5uCeIuGOTvV35DJWA0c3KdbebhKPPemLr+hrPEZo+yAd0dKXV2xCQcd7Y62Jd4793uNHyA92vRLNsZGKrzccsIpHzoSIRhLhT1hinNslU+a6yIJAgipv/WDx6/z5Di0Zt6BCt2/I6H+fxliGK2+Frk1iS4+fE8JKv95+7cya4/HVH69yET/GFaLFIlJt7rWz7lSe152apDOFn7IIdBGAs+8uapcvFamYoGYqXoJ3H9XTKNWJyImvxq6LGT9sQ/yUAjljEM1QMGo1LFaT03x+/+yizPzNE6GojL1V7OZJHITzq8TlnrNKkA699LysVwSXdySKA/PmRGmdGG3Ib+y/iNk5ySGXxqvviGJeblfWnkM5Iu7xUk+rtFbA6+CGmrXv3q7fvGH+OnZrkSEVeE7GcplMjdt/7bVg6XxbYHHV5YrP5OfkRVdOxbN3prXQSodchzuq//JZAygt2eM3qXu9LFG1zyL5BSKrs1rChYBp1f43ZRK4PKuS+GlEffOqB5NyX/OwsRLHbNXRfGAjvDX+HHFqY2n0RIUbdtdsiR6Ky7FXR+Xxp5dPDLQ9Q+JPaAJGJIExfclwApAcFAmVjeBos9WoMMIKEa8U5/3MI8eVMr3VVegk85Oq5um xktzZb+l 1As+y0/cf/l6pVVaJ0l7q3bugR3dwVNRngFJFj2g6dQMDgfH0rVoQbgVkAy/nhrK4GWT6wWRhjH38HmeLYbyIUhfbVCH7pInrIe3GpYT9A7F0X8lpTeRfR1GFvnxHVOWPdW/nhUyXdnmx4khH9MBhJBocbrBRU5+kUrsy10fyS8XtdQ4i+qFn7sY3YWaT/Qo4QNvpV0YQxtNHSzSREmABTBDr9KtRZRN+AnsRj4owu8DUFapAR6JlpFEu6GQY38B2jzYhpz+1IgdbyrGamRGATxn67t+m0PUSoSLt5bL/SdSBJl8G8G3NSoMDZ/xUj9HNcVjlXoyGEFWAoBPz9egMhFG3MlayD7HtclQ0w2N6WgvbnCJIe/fApGRow8LU7kHyvQ3Z7/itZp8JT9zkpQ8Pq+u2O5e+/anP5zSv4elptaRITtotj2qUuHlmPYPD3FbatTN+lzJX1W7bFqCeLw0JWmues7b+Zx5cFlQp 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: On 28.01.23 01:48, Jane Chu wrote: > On 1/26/2023 12:37 AM, David Hildenbrand wrote: >> On 25.01.23 23:09, Vishal Moola wrote: > [..] >> >> The issue is that we're not estimating the mapcount of the folio, so the >> name is very misleading ... I think you really want to avoid the term >> mapcount completely in that context. We're just using the #mappings of >> the first subpage to determine something differently. >> >> Thinking about it, I guess "folio_estimated_sharers()" might be what we >> actually want to name it. Then you can comment how we estimate sharers >> by looking at into how many page tables the first subpage is currently >> mapped, and assume the same holds true for the other subpages. >> >> It's unreliable because other subpages might behave differently, we >> might not be holding the pagelock to stabilize, and we're not looking at >> indirect mappings via the swapcache. But it's a comapratively good >> estimate for most scenarios I guess. >> > > Hmm, how about simply call it folio_hpage_mapcount(), > folio_firstpage_mapcount(), or, folio_cover_mapcount() ? All not better IMHO. folio_estimated_subpage_mapcount() is a bit too verbose for my taste and ... > > It is used to replace page_mapcount() in that sense - > https://lore.kernel.org/linux-mm/Y9MDJuPWsk9820xD@x1n/T/#me0531cfb9e82ad5ca88804c727d69cc6b9b33ffa > > if (flags & (MPOL_MF_MOVE_ALL) || > (flags & MPOL_MF_MOVE && folio_estimated_mapcount(folio) == 1 && > !hugetlb_pmd_shared(pte))) { > if (isolate_hugetlb(folio, qp->pagelist) && ... what we want to have here is an estimation on the number of sharers. [actually, we would want it precise, but that's hard to achieve ... ] -- Thanks, David / dhildenb