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Received: from willy by casper.infradead.org with local (Exim 4.98.2 #2 (Red Hat Linux)) id 1w7FL4-00000006wOx-3GNU; Mon, 30 Mar 2026 16:19:42 +0000 Date: Mon, 30 Mar 2026 17:19:42 +0100 From: Matthew Wilcox To: WANG Rui Cc: ziy@nvidia.com, ljs@kernel.org, Liam.Howlett@oracle.com, akpm@linux-foundation.org, baohua@kernel.org, baolin.wang@linux.alibaba.com, brauner@kernel.org, clm@fb.com, david@kernel.org, dev.jain@arm.com, dsterba@suse.com, jack@suse.cz, lance.yang@linux.dev, linux-btrfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-mm@kvack.org, mhocko@suse.com, npache@redhat.com, rppt@kernel.org, ryan.roberts@arm.com, shuah@kernel.org, songliubraving@fb.com, surenb@google.com, vbabka@kernel.org, viro@zeniv.linux.org.uk Subject: Re: [PATCH v1 05/10] mm/huge_memory: remove READ_ONLY_THP_FOR_FS from file_thp_enabled() Message-ID: References: <20260330160942.173324-1-r@hev.cc> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260330160942.173324-1-r@hev.cc> X-Rspam-User: X-Stat-Signature: 5dhew1ejxasipwsyz5p7r1zry1qui9g7 X-Rspamd-Queue-Id: 93994140011 X-Rspamd-Server: rspam09 X-HE-Tag: 1774887594-513833 X-HE-Meta: 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 biYb0vZq qHojpujpy5V7i5EA0HOktTIRMqeBDmF2YQXk8D04J/M/y9ASCXndRXBVEEEHi8cIhPAEQVd1nBgK6HcJMGtZK61dcOgKsNQo4CqQ5KjhF15xR4aHu+qraMpmS+sT754fPKfLhquPjwKChlfnfCwvvplV2gH4GXxAhVIBP49W3+/K4uB1SFM/6G+MeYNhRT3sPsWIJbffrBMr6fuX11QcaR+NTjEnBZT9pZhYuEAl5v5GrHCt05fVBH/ug4vTHod7Q4F87iuuqjR3MSI0RwoQ2j3sxiWQSi0TBTEr9QzX6j3nNv1ktou161vjyrPr5Vg9ZgMwQ Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Mar 31, 2026 at 12:09:42AM +0800, WANG Rui wrote: > Given the diversity of filesystems in use, each one requires dedicated > engineering effort to implement and validate large folio support, and > that assumes both sufficient resources and prioritization on the > filesystem side. Even after support lands, coverage across different > base page sizes and configurations may take additional time to mature. > > What I am really concerned about is the transition period: if filesystem > support is not yet broadly ready, while we have already removed the > fallback path, we may end up in a situation where PMD-sized mappings > become effectively unavailable on many systems for some time. > > This is not about the long-term direction, but about the timing and > practical readiness. If we leave this fallback in place, we'll never get filesystems to move forward. It's time to rip off this bandaid; they've got eight months before the next stable kernel. I've talked to them about it for years LSFMM 2022: https://lwn.net/Articles/893512/ LSFMM 2023: https://lwn.net/Articles/931794/ LSFMM 2024: https://lwn.net/Articles/973565/ LSFMM 2025: https://lwn.net/Articles/1015320/ (and earlier, but I think I've made my point)