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Thu, 19 Feb 2026 17:14:23 -0500 (EST) Date: Thu, 19 Feb 2026 22:14:17 +0000 From: Kiryl Shutsemau To: Dave Hansen Cc: lsf-pc@lists.linux-foundation.org, linux-mm@kvack.org, x86@kernel.org, linux-kernel@vger.kernel.org, Andrew Morton , David Hildenbrand , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , Lorenzo Stoakes , "Liam R. Howlett" , Mike Rapoport , Matthew Wilcox , Johannes Weiner , Usama Arif Subject: Re: [LSF/MM/BPF TOPIC] 64k (or 16k) base page size on x86 Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 4411B4000B X-Stat-Signature: xszpaue5w5bqszxr7pdoxxiymo5k4q58 X-Rspam-User: X-HE-Tag: 1771539268-983187 X-HE-Meta: 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 5k1LT/kF 20uSDZDUPPxp2Hwd0hWb9puEETP7BTAyxv9FfgH6LIqdZtqkglYUCqXP9HzaB/2ZentLa06oLHj0KcHR91gSjShC0OCNMf4++K3jI3gAJamZkMM4V14BRX7SFsTvxSZxVXt2w69L5R66zROXNx+uqYbsGjxfU1fawj+Pqyf5OkSQqnYDtD9hYyhf5aVtaVI2Hz9+uSZ4BouZEHX20HVDTkJhz4iNy32Fh+22LtKkdfKJkkfWYAoqbU78r7SCTHYV3QF4vTM4ti7sLOjWUeC/DBgb/Tw== 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 Thu, Feb 19, 2026 at 09:30:36AM -0800, Dave Hansen wrote: > On 2/19/26 07:08, Kiryl Shutsemau wrote: > ... > > The patchset is large: > > > > 378 files changed, 3348 insertions(+), 3102 deletions(-) > > A few notes about the diffstats: > > $ git diff v6.17..HEAD arch/x86 | diffstat | tail -1 > 105 files changed, 874 insertions(+), 843 deletions(-) > $ git diff v6.17..HEAD mm | diffstat | tail -1 > 53 files changed, 1136 insertions(+), 1069 deletions(-) > > The vast, vast majority of this seems to be the renames. Stuff like: > > > - new = round_down(new, PAGE_SIZE); > > + new = round_down(new, PTE_SIZE); > > or even less worrying: > > > -int set_direct_map_valid_noflush(struct page *page, unsigned nr, bool valid); > > +int set_direct_map_valid_noflush(struct page *page, unsigned numpages, bool valid); > > That stuff obviously needs to be audited but it's far less concerning > than the logic changes. > > So just for review sanity, if you go forward with this, I'd very much > appreciate a strong separation of the purely mechanical bits from any > logic changes. That's the plan. That's the only way I can keep myself sane :P > > On x86, page tables are allocated from the buddy allocator and if PG_SIZE > > is greater than 4 KB, we need a way to pack multiple page tables into a > > single page. We could use the slab allocator for this, but it would > > require relocating the page-table metadata out of struct page. > > Others mentioned this, but I think this essentially gates what you are > doing behind a full tree conversion over to ptdescs. I have not followed ptdescs closely. Need to catch up. For PoC, I will just waste full order-0 page for page table. Packing is not required for correctness. > The most useful thing we can do with this series is look at it and > decide what _other_ things need to get done before the tree could > possibly go in that direction, like ptdesc or a the disambiguation > between PTE_SIZE and PG_SIZE that you've kicked off here. Right. -- Kiryl Shutsemau / Kirill A. Shutemov