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Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Lance Yang , Chris Li , Kairui Song , Kemeng Shi , Nhat Pham , Baoquan He , Youngjun Park Subject: Re: [PATCH] mm/huge_memory: Fix outdated comment about freeing subpages in __folio_split Message-Id: <20260428060115.84c55bcf72315c01b86e0c90@linux-foundation.org> In-Reply-To: References: <20260423034917.8234-1-baohua@kernel.org> <17a3bc38-0d97-4316-b2fb-02a91202c504@kernel.org> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: A5A0510000C X-Stat-Signature: mo8iakoxha4wcz45jqaskz34cjzk1o63 X-Rspam-User: X-HE-Tag: 1777381277-465682 X-HE-Meta: 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 PWJsR26o 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, 28 Apr 2026 18:32:40 +0800 Barry Song wrote: > On Tue, Apr 28, 2026 at 6:08 PM David Hildenbrand (Arm) > wrote: > > > > On 4/28/26 12:05, Barry Song wrote: > > > On Mon, Apr 27, 2026 at 3:42 PM David Hildenbrand (Arm) > > > wrote: > > >> > > >> On 4/26/26 22:42, Barry Song wrote: > > >>> On Thu, Apr 23, 2026 at 8:36 PM David Hildenbrand (Arm) > > >>> wrote: > > >>> > > >>> Thanks, david! would it make more sense to add “when > > >>> CONFIG_PAGE_MAPCOUNT is enabled” at the end of the > > >>> sentence? > > >> > > >> Better to phrase it in a way that doesn't even require these details :) > > >> > > >> Do we even need this detail in the patch description? > > > > > > What about: > > > > > > The comment appears to be outdated. add_to_swap() no longer exists, > > > and the explanation of why we need to call put_page() after > > > splitting could be made more general. > > > > Jup :) > > Thanks! > Hi Andrew, would you like to make the change in the > changelog, or would you prefer that I send a new version? This? From: "Barry Song (Xiaomi)" Subject: mm/huge_memory: fix outdated comment about freeing subpages in __folio_split Date: Thu, 23 Apr 2026 11:49:17 +0800 The comment appears to be outdated. add_to_swap() no longer exists, and the explanation of why we need to call put_page() after splitting could be made more general. Link: https://lore.kernel.org/20260423034917.8234-1-baohua@kernel.org Signed-off-by: Barry Song (Xiaomi) Acked-by: David Hildenbrand (Arm) Acked-by: Zi Yan Cc: Lorenzo Stoakes Cc: Baolin Wang Cc: Liam R. Howlett Cc: Nico Pache Cc: Ryan Roberts Cc: Dev Jain Cc: Lance Yang Cc: Chris Li Cc: Kairui Song Cc: Kemeng Shi Cc: Nhat Pham Cc: Baoquan He Cc: Youngjun Park Signed-off-by: Andrew Morton --- mm/huge_memory.c | 9 ++++----- 1 file changed, 4 insertions(+), 5 deletions(-) --- a/mm/huge_memory.c~mm-huge_memory-fix-outdated-comment-about-freeing-subpages-in-__folio_split +++ a/mm/huge_memory.c @@ -4190,11 +4190,10 @@ fail: folio_unlock(new_folio); /* - * Subpages may be freed if there wasn't any mapping - * like if add_to_swap() is running on a lru page that - * had its mapping zapped. And freeing these pages - * requires taking the lru_lock so we do the put_page - * of the tail pages after the split is complete. + * Subpages whose mapping has been zapped may be freed + * earlier, but freeing them requires taking the + * lru_lock, so we defer put_page() on tail pages until + * after the split completes. */ free_folio_and_swap_cache(new_folio); } _