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b=NweolyGXKEajQ0RagK6sfKNXR3ZzC9vSVU2YLniuEU+Glx+awY5/0FLd0SJ4c2fTA ZEawMCjKSwiuOqJZycIboFWAUXIsXCV3AjZmpmSiUxaUzweLj7Xb3OINPKYt2KuZct pps6h9ZusRXlL+CGq/ZIMQh5wOf0Wucq5+apl8w/QFyWX9GYCW0dUl/bCkG/tbUm2L LOOvm+uurETXlZAVKh1uT8YMvaSSxBD4qqvZJ7FqwYsJXg8WqcAInBwV3ljQt/QVJB 4kWeE2s44qxGxrcfoOjgVQp0UjmsVLGZGNOtub+PELBiymmugD3s3Hn2+Rf+jegYJ0 jT12W2JGCFVUw== Date: Wed, 27 May 2026 12:56:35 +0100 From: Lorenzo Stoakes To: tao Cc: catalin.marinas@arm.com, will@kernel.org, tglx@kernel.org, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, akpm@linux-foundation.org, david@kernel.org, willy@infradead.org, sj@kernel.org, kees@kernel.org, luizcap@redhat.com, zhangjiao2@cmss.chinamobile.com, kas@kernel.org, hpa@zytor.com, liam@infradead.org, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, jack@suse.cz, riel@surriel.com, harry@kernel.org, jannh@google.com, jgg@ziepe.ca, jhubbard@nvidia.com, peterx@redhat.com, ziy@nvidia.com, baolin.wang@linux.alibaba.com, npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, lance.yang@linux.dev, xu.xin16@zte.com.cn, chengming.zhou@linux.dev, nao.horiguchi@gmail.com, matthew.brost@intel.com, joshua.hahnjy@gmail.com, rakie.kim@sk.com, byungchul@sk.com, gourry@gourry.net, ying.huang@linux.alibaba.com, apopple@nvidia.com, pfalcato@suse.de, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, damon@lists.linux.dev, shakeel.butt@linux.dev, ryncsn@gmail.com, 21cnbao@gmail.com, jparsana@google.com, dvander@google.com, zhangji1@honor.com, wangzicheng@honor.com Subject: Re: [PATCH 03/15] mm: introduce anon_vma_tree_t for multiple anon_vma topologies Message-ID: References: <20260527110147.17815-1-tao.wangtao@honor.com> <20260527110147.17815-4-tao.wangtao@honor.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260527110147.17815-4-tao.wangtao@honor.com> X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: A72FCC000A X-Stat-Signature: 6t6c4r69icd4tjo75r4osi878m7swop3 X-HE-Tag: 1779883012-142051 X-HE-Meta: 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 +oUyFwUa c2DwHzFY/BEWI6+ks5uHFpH7JDUY4Q+GZVSa9r9HbsptbMeNegz+KiAJWeMDqQvw8SQImfpL8wM0mR3Vj4m13JpeT6NqJaeRPbLhvLPyOJ7N9Ias+jeBL7ixTv/Z6fFhCqqjb3N4TLqJQAQ9owe4sfHMbfNcYTZKc7jAIFU9uKPHhtM13e4w69W8Jx75+Q6i/2tIHKGBJA/Fy+2dWvYgKPIinhcUOC14PS4sYwRtjcvXzcnFma6YbHTftByIJxKz1T9NgaZvo4J6O1B1OSE6UQnYtPyl3pvqU713yX6ihBzvmOG1TKBEW87N3MYA3DsyUGW+XqB2Hv2Fb0N+QC5KTO3ScnZ1XQzAmm6uSBf5WvD/pk7rgCA+dT1vrENdS7ssFTMyaOhrcgb6HF0DeZSnYv3WMKpqAprG+gEaHMuGf3HJGcuffsa9yh1t00NsSZ9FF5hxprb7UBGZXGns= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, May 27, 2026 at 07:01:35PM +0800, tao wrote: > Prepare for upcoming ANON_VMA_LAZY support and RCU-based lockless rmap > traversal by clearly separating anon_vma topology handling from the > anon_rmap semantics. RCU is not 'lockless'... and if you truly get RCU semantics you break a bunch of stuff as I found out. > > Prepare for supporting multiple anon_vma topologies by introducing > lightweight abstractions used by the VMA and rmap code. > > Introduce anon_vma_tree_t as the type stored in vma->anon_vma: > > typedef unsigned long anon_vma_tree_t; > > It represents a tagged pointer encoding a reference to the anon_vma > topology. The low bits are reserved as type tags to distinguish > different implementations (e.g. regular anon_vma and lazy anon_vma). > This keeps the VMA representation compact while allowing the topology > to evolve without changing the VMA layout. > > Signed-off-by: tao The commit message is at least better on this one, but this approach is again, predicated on extending a broken abstraction. You could have saved time and effort by coming forward with this earlier to the community. You're also adding a bunch more messy code on top of anon_vma. It's just the wrong direction. > --- > include/linux/mm_types.h | 3 +++ > mm/internal.h | 54 ++++++++++++++++++++++++++++++++++++++++ > 2 files changed, 57 insertions(+) > > diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h > index a308e2c23b82..5f4961ea1572 100644 > --- a/include/linux/mm_types.h > +++ b/include/linux/mm_types.h > @@ -917,6 +917,9 @@ struct vm_area_desc { > struct mmap_action action; > }; > > +/* Tagged pointer stored in vma->anon_vma. Low bits encode anon_vma type. */ > +typedef unsigned long anon_vma_tree_t; > + > /* > * This struct describes a virtual memory area. There is one of these > * per VM-area/task. A VM area is any part of the process virtual memory > diff --git a/mm/internal.h b/mm/internal.h > index 5a2ddcf68e0b..76544ad44ff0 100644 > --- a/mm/internal.h > +++ b/mm/internal.h > @@ -246,6 +246,60 @@ static inline void anon_vma_unlock_read(struct anon_vma *anon_vma) > up_read(&anon_vma->root->rwsem); > } > > +/* anon_vma_tree_t APIs */ > + > +static inline anon_vma_tree_t make_anon_vma_tree(struct anon_vma *anon_vma) > +{ > + return (anon_vma_tree_t)anon_vma; > +} You're literally returning an unsigned long of an anon_vma here? Why is the anon_rmap_t a wrapped struct and this an unsigned long? > + > +static inline struct anon_vma *anon_vma_tree_anon_vma(anon_vma_tree_t anon_tree) > +{ > + return (struct anon_vma *)anon_tree; > +} The anon_tree is an anon_vma? What? And it's a tagged pointer but we don't bother clearing any bits right?...! > + > +static inline void anon_vma_tree_lock_write(anon_vma_tree_t anon_tree) > +{ > + struct anon_vma *anon_vma = anon_vma_tree_anon_vma(anon_tree); > + > + anon_vma_lock_write(anon_vma); > +} > + > +static inline int anon_vma_tree_trylock_write(anon_vma_tree_t anon_tree) > +{ > + struct anon_vma *anon_vma = anon_vma_tree_anon_vma(anon_tree); > + > + return anon_vma_trylock_write(anon_vma); > +} > + > +static inline void anon_vma_tree_unlock_write(anon_vma_tree_t anon_tree) > +{ > + struct anon_vma *anon_vma = anon_vma_tree_anon_vma(anon_tree); > + > + anon_vma_unlock_write(anon_vma); > +} > + > +static inline void anon_vma_tree_lock_read(anon_vma_tree_t anon_tree) > +{ > + struct anon_vma *anon_vma = anon_vma_tree_anon_vma(anon_tree); > + > + anon_vma_lock_read(anon_vma); > +} > + > +static inline int anon_vma_tree_trylock_read(anon_vma_tree_t anon_tree) > +{ > + struct anon_vma *anon_vma = anon_vma_tree_anon_vma(anon_tree); > + > + return anon_vma_trylock_read(anon_vma); > +} > + > +static inline void anon_vma_tree_unlock_read(anon_vma_tree_t anon_tree) > +{ > + struct anon_vma *anon_vma = anon_vma_tree_anon_vma(anon_tree); > + > + anon_vma_unlock_read(anon_vma); > +} > + You keep adding more and more code on top of the existing mess. This is NOT what we want. > struct anon_vma *folio_get_anon_vma(const struct folio *folio); > > /* Operations which modify VMAs. */ > -- > 2.17.1 >