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Howlett" , Jens Axboe , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org, mcgrof@kernel.org, gost.dev@samsung.com, kernel@pankajraghav.com, tytso@mit.edu Subject: Re: [RFC v2 0/3] Decoupling large folios dependency on THP Message-ID: References: <20251206030858.1418814-1-p.raghav@samsung.com> <64291696-C808-49D0-9F89-6B3B97F58717@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: 3CB81A000D X-Rspam-User: X-Rspamd-Server: rspam12 X-Stat-Signature: kpwh9azqwiyti3ij5tywrt5p6d9ixpwm X-HE-Tag: 1765438693-124797 X-HE-Meta: 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 lQa4RzbL luQpuVDZnfv1zVy+8YcWkKHoV05VoBCTMGPgQhXn2vegX2Ta6/qG7wwJ2C7+HX4GcZnD580BiNaW6cMlXgm0tqBLBa1jQYdkjXVLb9tcxOZd7wVpA5dTb+YVH0FTo53OE94aBhLXGmPbVLCcexLSbzOfY1iDUipMomm2+39hzirpqaX+TBIqt8YgNlt+NVWNUMlarWfEGR7bnEW6eCsr34ccDGEajqiv6B/1Qx2yxSGhXiOy+W9UuR5F0LJtCy8GuMLcO 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 Wed, Dec 10, 2025 at 11:37:51AM -0500, Zi Yan wrote: > On 9 Dec 2025, at 23:27, Matthew Wilcox wrote: > > > On Tue, Dec 09, 2025 at 11:03:23AM -0500, Zi Yan wrote: > >> I wonder if core-mm should move mTHP code out of CONFIG_TRANSPARENT_HUGEPAGE > >> and mTHP might just work. Hmm, folio split might need to be moved out of > >> mm/huge_memory.c in that case. khugepaged should work for mTHP without > >> CONFIG_TRANSPARENT_HUGEPAGE as well. OK, for anon folios, the changes might > >> be more involved. > > > > I think this is the key question to be discussed at LPC. How much of > > I am not going, so would like to get a summary afterwards. :) You can join the fun at meet.lpc.events, or there's apparently a youtube stream. > > the current THP code should we say "OK, this is large folio support > > and everybody needs it" and how much is "This is PMD (or mTHP) support; > > this architecture doesn't have it, we don't need to compile it in". > > I agree with most of it, except mTHP part. mTHP should be part of large > folio, since I see mTHP is anon equivalent to file backed large folio. > Both are a >0 order folio mapped by PTEs (ignoring to-be-implemented > multi-PMD mapped large folios for now). Maybe we disagree about what words mean ;-) When I said "mTHP" what I meant was "support for TLB entries which cover more than one page". I have no objection to supporting large folio allocation for anon memory because I think that's beneficial even if there's no hardware support for TLB entries that cover intermediate sizes between PMD and PTE.