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Mon, 23 Feb 2026 03:59:49 -0800 (PST) Date: Mon, 23 Feb 2026 11:59:48 +0000 From: Wei Yang To: "David Hildenbrand (Arm)" Cc: Zi Yan , Wei Yang , Linux MM Subject: Re: A potential refcount issue during __folio_split Message-ID: <20260223115948.sbylmtqhznmabcth@master> Reply-To: Wei Yang References: <20260222010425.gbsjzhrew3pg4qrw@master> <20260222010708.uohpmddmzaa4i4ic@master> <6346656B-7518-4A55-8DEF-C2E975714C8B@nvidia.com> <3e22afe6-ecf7-4180-9287-c48fea7b8be1@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <3e22afe6-ecf7-4180-9287-c48fea7b8be1@kernel.org> User-Agent: NeoMutt/20170113 (1.7.2) X-Stat-Signature: p64oodhf1nsqf5t6boxsuf576nruftuw X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 6ADC240002 X-HE-Tag: 1771847991-107278 X-HE-Meta: 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 8dBwVwtQ 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Feb 23, 2026 at 10:23:11AM +0100, David Hildenbrand (Arm) wrote: >> BTW, in the folio world, I do not think it is possible to perform the aforementioned >> split_huge_page_to_list_to_order() pattern any more, since you always work on folio, >> the head. Unless there is a need of getting hold of a tail after-split folio after >> a folio split, the pattern would be: >> >> tail_page = folio_page(folio, N); >> >> folio_get(folio); >> folio_lock(folio); >> folio_split(folio, ..., /* new parameter: lock_at = */ tail_page, ...); >> tail_folio = page_folio(tail_page); >> folio_unlock(tail_folio); >> folio_put(tail_folio); > Missed this. Agree. >Agreed. Maybe it would be even nicer if the split function could return the >new folio directly. > >folio_get(folio); >folio_lock(folio); >split_folio = folio_split_XXX(folio, ..., tail_page, ...); >if (IS_ERR_VALUE(split_folio)) { > ... >} >folio_unlock(split_folio); >folio_put(split__folio); > I am afraid it would be complicated? Well, we don't have this usecase now, could decide it when we do need it. >-- >Cheers, > >David -- Wei Yang Help you, Help me