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Wed, 30 Sep 2026 04:24:24 +0000 X-Mizu-Trace-ID: e9b7e58d84d31462 X-Migadu-Flow: FLOW_OUT From: Lance Yang To: songmuchun@bytedance.com Cc: maddy@linux.ibm.com, rppt@kernel.org, akpm@linux-foundation.org, david@kernel.org, mpe@ellerman.id.au, npiggin@gmail.com, chleroy@kernel.org, ritesh.list@gmail.com, sshegde@linux.ibm.com, ljs@kernel.org, liam@infradead.org, vbabka@kernel.org, surenb@google.com, mhocko@suse.com, qi.zheng@linux.dev, linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, muchun.song@linux.dev, Lance Yang Subject: Re: [PATCH v3 1/6] mm/sparse-vmemmap: drop VMEMMAP_POPULATE_DAX Date: Wed, 30 Sep 2026 12:24:14 +0800 Message-ID: <20260930042414.97599-1-lance.yang@linux.dev> X-Mailer: git-send-email 2.49.0 In-Reply-To: <20260929053231.66085-2-songmuchun@bytedance.com> References: <20260929053231.66085-2-songmuchun@bytedance.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Stat-Signature: ennggsqeto9xrbfk4qwbbj8e56owoa56 X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: CAC1E180003 X-HE-Tag: 1790742267-134061 X-HE-Meta: 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 8T9hElLP cDnyxk8Bt+e6Nsq+nd50a3Nluy8CxjpX21Gs+KYzesTP+oH3XUKst6oGlXkHAVwk8OVmiYa/alpI4UVI2CzYzmCQZsyD4ApLeRltJ3frw8msR0lyB0+EHQNUcaxsJWOf9L1n5NwFOzzLFTYMAn2a+CH36RtAb2InjvMCbIVVoxawZxULCGYDmIi8i/e2vcf5ggs+iuqiCtsTKV5gb87EHLME51DqD/qMOFY5LRkzYDaKLDA0hVml4sXpdeaL7caf/3+gpkIa1HqU7iIiB+PfLohJkyPpBIc0BffPtCvTK0eh1kGSnA9kkpcO57avthpW5c5GSbYCJ2YbvTB+6D7R5CQL4quGWNg+f3+xtOAsTJ2wLgT5eGtBfpNEC7SO8Wvx67RrL Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Sep 29, 2026 at 01:32:26PM +0800, Muchun Song wrote: >VMEMMAP_POPULATE_DAX currently distinguishes DAX vmemmap population in >two places: it keeps allocations on the normal path and takes a reference >when a backing page is supplied for reuse. > >After Device DAX switched to the common per-zone shared tail page, both >conditions can be determined locally. DAX supplies ptpfn for every shared >tail mapping and requests an allocation only for compound head mappings, >whose PFNs are not optimizable. Therefore, vmemmap_optimizable_pfn() alone >selects the correct allocation path. > >When ptpfn is supplied, the caller is reusing an existing backing page. >Once the slab allocator is available, take a reference for each reused >mapping to balance the release performed by vmemmap_free(). Although the >buddy allocator is available before slab, no vmemmap population occurs in >that interval. Earlier mappings are backed by memblock/reserved memory and >do not need page reference accounting. > >Remove VMEMMAP_POPULATE_DAX and the flags argument from the vmemmap >population helpers. > >Signed-off-by: Muchun Song >Acked-by: Qi Zheng >--- LGTM! Feel free to add: Reviewed-by: Lance Yang