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([2620:10d:c090:500::797a]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-2b7a16eab80sm11714614eec.9.2026.01.30.09.10.12 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 30 Jan 2026 09:10:13 -0800 (PST) Message-ID: <00d098da-0d01-43f9-9efb-c18b6e8a771e@gmail.com> Date: Fri, 30 Jan 2026 09:10:11 -0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH] btrfs: defer freeing of subpage private state to free_folio To: Matthew Wilcox , Qu Wenruo Cc: boris@bur.io, clm@fb.com, dsterba@suse.com, linux-btrfs@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@meta.com, "linux-fsdevel@vger.kernel.org" References: <20260129230822.168034-1-inwardvessel@gmail.com> <776e54f6-c9b7-4b22-bde5-561dc65c9be7@gmx.com> Content-Language: en-US From: JP Kobryn In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 1/29/26 9:14 PM, Matthew Wilcox wrote: > On Fri, Jan 30, 2026 at 01:46:59PM +1030, Qu Wenruo wrote: >> Another question is, why only two fses (nfs for dir inode, and orangefs) are >> utilizing the free_folio() callback. > > Alas, secretmem and guest_memfd are also using it. Nevertheless, I'm > not a fan of this interface existing, and would prefer to not introduce > new users. Like launder_folio, which btrfs has also mistakenly used. > The part that felt concerning is how the private state is lost. If release_folio() frees this state but the folio persists in the cache, users of the folio afterward have to recreate the state. Is that the expectation on how filesystems should handle this situation? In the case of the existing btrfs code, when the state is recreated (in subpage mode), the bitmap data and lock states are all zeroed.