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Sat, 05 Sep 2026 08:20:25 +0000 X-Mizu-Trace-ID: 1b4d3cf39591adcd X-Migadu-Flow: FLOW_OUT Message-ID: <1143901c-5036-4b79-8135-21ce57075136@linux.dev> Date: Sat, 5 Sep 2026 16:20:16 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 05/11] mm/sparse-vmemmap: set section order for device DAX To: Muchun Song , Andrew Morton , David Hildenbrand , Oscar Salvador , Madhavan Srinivasan , Michael Ellerman , Jonathan Corbet Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-doc@vger.kernel.org, Muchun Song , Lorenzo Stoakes , Mike Rapoport , Nicholas Piggin , Christophe Leroy , Randy Dunlap References: <20260831075342.57563-1-songmuchun@bytedance.com> <20260831075342.57563-6-songmuchun@bytedance.com> From: Qi Zheng In-Reply-To: <20260831075342.57563-6-songmuchun@bytedance.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 7EF4620006 X-Stat-Signature: es5eue5b4asxrqhu5wfojmdydjz744yn X-HE-Tag: 1788596430-837117 X-HE-Meta: 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 frKy3c5U Ab51pNmX1w3OnWJYEsvxc2LzZHq5Zin3FEmkuqgy/3NiwEp87IirAFfqw84zEIP6zXf8tMa4EhJRIYvP1HMvq1xXaDjsS0KW1N0NU/wPrms93fbu/27N26YTUBAyqQvEtO1p5Dw0s1FQ1f9m9Y9U76ToiUyzMVe0gaWXUdrQAhQc16K5GhdSjziSYb+B8OJy0Gt73wnf0jkoTSjcjZQauXLOufJJ8zC7qbtn+f707QAlJLJeNmAY3S156E+FYRCW3lSJe65QP7TW9TWfbz4Es+tLR5tMAEcd8GOI0YZNeQDyuZUU= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hi Muchun, On 8/31/26 3:53 PM, Muchun Song wrote: > Device DAX can use vmemmap optimization only when a full section is > populated with a compound-page geometry. Record that geometry in the > section order before populating the section, so later vmemmap accounting > and population decisions can use the section state directly. > > Clear the section order when the section becomes empty again. Also reject > partial additions to a section that already has optimized vmemmap mappings, > because a section cannot safely mix optimized and ordinary vmemmap layouts. Perhaps we should explain why they cannot be safely mixed. > > Partial additions continue to use ordinary vmemmap population, so they do > not save vmemmap memory. Such additions are uncommon, and the lost saving > is negligible. > > Signed-off-by: Muchun Song > --- > mm/mm_init.c | 13 ++++--------- > mm/sparse-vmemmap.c | 16 ++++++++++++---- > 2 files changed, 16 insertions(+), 13 deletions(-) > Also, the issue sashiko reported looks like it was pre-existing, not introduced by this patch. So: Acked-by: Qi Zheng Thanks, Qi