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Howlett" , Lorenzo Stoakes , Vlastimil Babka , Jann Horn Subject: Re: [PATCH v3 20/20] mm: stop maintaining the per-page mapcount of large folios (CONFIG_NO_PAGE_MAPCOUNT) Message-ID: <20251015004543.md5x4cjtkyjzpf4b@master> Reply-To: Wei Yang References: <20250303163014.1128035-1-david@redhat.com> <20250303163014.1128035-21-david@redhat.com> <20251014122335.dpyk5advbkioojnm@master> <71380b43-c23c-42b5-8aab-f158bb37bc75@redhat.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20170113 (1.7.2) On Tue, Oct 14, 2025 at 04:38:38PM +0200, David Hildenbrand wrote: >On 14.10.25 16:32, Matthew Wilcox wrote: >> On Tue, Oct 14, 2025 at 02:59:30PM +0200, David Hildenbrand wrote: >> > > As commit 349994cf61e6 mentioned, we don't support partially mapped PUD-sized >> > > folio yet. >> > >> > We do support partially mapped PUD-sized folios I think, but not anonymous >> > PUD-sized folios. >> >> I don't think so? The only mechanism I know of to allocate PUD-sized >> chunks of memory is hugetlb, and that doesn't permit partial mappings. > >Greetings from the latest DAX rework :) After a re-think, do you think it's better to align the behavior between CONFIG_NO_PAGE_MAPCOUNT and CONFIG_PAGE_MAPCOUNT? It looks we treat a PUD-sized folio partially_mapped if CONFIG_NO_PAGE_MAPCOUNT, but !partially_mapped if CONFIG_PAGE_MAPCOUNT, if my understanding is correct. > >-- >Cheers > >David / dhildenb -- Wei Yang Help you, Help me