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Thu, 12 Mar 2026 01:19:11 -0700 (PDT) Date: Thu, 12 Mar 2026 08:19:10 +0000 From: Wei Yang To: Dev Jain Cc: "Lorenzo Stoakes (Oracle)" , akpm@linux-foundation.org, axelrasmussen@google.com, yuanchu@google.com, david@kernel.org, hughd@google.com, chrisl@kernel.org, kasong@tencent.com, weixugc@google.com, Liam.Howlett@oracle.com, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, riel@surriel.com, harry.yoo@oracle.com, jannh@google.com, pfalcato@suse.de, baolin.wang@linux.alibaba.com, shikemeng@huaweicloud.com, nphamcs@gmail.com, bhe@redhat.com, baohua@kernel.org, youngjun.park@lge.com, ziy@nvidia.com, kas@kernel.org, willy@infradead.org, yuzhao@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, ryan.roberts@arm.com, anshuman.khandual@arm.com Subject: Re: [PATCH 8/9] mm/rmap: introduce folio_try_share_anon_rmap_ptes Message-ID: <20260312081910.ux6p63qtde3r77rv@master> Reply-To: Wei Yang References: <20260310073013.4069309-1-dev.jain@arm.com> <20260310073013.4069309-9-dev.jain@arm.com> <3ff22f08-5617-4c05-8fa0-1d808806e322@lucifer.local> 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 Wed, Mar 11, 2026 at 01:39:25PM +0530, Dev Jain wrote: > [...] >>> diff --git a/include/linux/rmap.h b/include/linux/rmap.h >>> index 1b7720c66ac87..7a67776dca3fe 100644 >>> --- a/include/linux/rmap.h >>> +++ b/include/linux/rmap.h >>> @@ -712,9 +712,13 @@ static __always_inline int __folio_try_share_anon_rmap(struct folio *folio, >>> VM_WARN_ON_FOLIO(!PageAnonExclusive(page), folio); >>> __folio_rmap_sanity_checks(folio, page, nr_pages, level); >>> >>> + /* We only clear anon-exclusive from head page of PMD folio */ >> >> Is this accurate? David? I thought anon exclusive was per-subpage for any large >> folio...? > >The current behaviour is to do this only. I was also surprised with this, >so I had dug in and found out: > >https://lore.kernel.org/all/20220428083441.37290-13-david@redhat.com/ > >where David says: > >"Long story short: once >PTE-mapped, we have to track information about exclusivity per sub-page, >but until then, we can just track it for the compound page in the head >page and not having to update a whole bunch of subpages all of the time >for a simple PMD mapping of a THP." > Thanks for digging. One tiny thing: Now we have a comment in PageAnonExclusive(), which says: /* * HugeTLB stores this information on the head page; THP keeps it per * page */ This may confuse readers? Not your fault, just want to point it out. -- Wei Yang Help you, Help me