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Sun, 30 Aug 2026 06:19:41 -0700 (PDT) Received: from KASONG-MC4 ([101.32.222.185]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-398a2f5187fsm3023979a91.1.2026.08.30.06.19.35 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 30 Aug 2026 06:19:40 -0700 (PDT) Date: Sun, 30 Aug 2026 21:19:32 +0800 From: Kairui Song To: "David Hildenbrand (Arm)" Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , Lorenzo Stoakes , Zi Yan , Baolin Wang , "Liam R. Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Lance Yang , Usama Arif , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Chris Li , Kemeng Shi , Nhat Pham , Baoquan He , Barry Song , Youngjun Park , Shivam Kalra Subject: Re: [PATCH v3 15/18] mm/huge_memory: lift order-0 restriction for swapcache split Message-ID: References: <20260821-swap-thp-cleanup-v3-0-9b43f5163238@tencent.com> <20260821-swap-thp-cleanup-v3-15-9b43f5163238@tencent.com> <79aaca61-4e4d-4f1c-9492-41b00bf6ff04@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <79aaca61-4e4d-4f1c-9492-41b00bf6ff04@kernel.org> X-Stat-Signature: cqam1rt3pm74txidmia9sf97ry6wpy9f X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 94D96A0007 X-Rspam-User: X-HE-Tag: 1788095982-726231 X-HE-Meta: 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 Fm+7dv5a 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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 Thu, Aug 27, 2026 at 10:22:56PM +0800, David Hildenbrand (Arm) wrote: > On 8/27/26 19:48, Kairui Song wrote: > > On Fri, Aug 28, 2026 at 12:51 AM David Hildenbrand (Arm) > > wrote: > >> > >> On 8/20/26 20:55, Kairui Song via B4 Relay wrote: > >>> From: Kairui Song > >>> > >>> The restriction that swapcache folios can only be uniformly split to > >>> order 0 dates back to when the swap cache was managed via address_space > >>> mapping (swap_address_space). The old split loop only created order-0 > >>> sub-folios with a fixed stride, so non-uniform split and non-zero order > >>> were rightfully blocked. > >>> > >>> After the swap cache switched to swap table under a cluster lock, > >>> __swap_cache_replace_folio already gained the ability to replace any > >>> number of entries for any sub-folio size in one cluster, and the old > >>> swap_address_space locking and limit was removed. The restriction > >>> became obsolete but persisted through multiple refactorings. > >>> > >>> Drop it now: swapcache folios can be split to any supported order with > >>> either uniform or non-uniform split, except order-1 which is not > >>> supported for anon folios. Mappingless swap cache folios could be either > >>> anon or shmem, so for now we just simply forbid order-1 for all swapcache. > >>> > >>> Acked-by: Zi Yan > >>> Signed-off-by: Kairui Song > >>> --- > >> > >> In contrast to the other cleanup patches, this patch changes behavior. > >> > >> I would suggest to send all cleanups first, and send this out separately, such > >> that it gets proper attention and doesn't get buried in a sequence of > >> harmlessly-looking cleanups :) > > > > No problem, send this later then :) > > On second thought, the > > "mm/huge_memory: allow splitting mappingless swap cache folios" > > is already such a change. And I guess only having both these behavior-changing > things separated from the cleanups might be harder, right? It seems actually not hard to drop these two, and keep mostly of the cleanup, will send a V4 as pure cleanup and tiny fixes. And without these two change it actually looks cleaner, and shorter to review. Swap cache support can done seperately later.