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[67.164.59.41]) by smtp.gmail.com with ESMTPSA id a92af1059eb24-11b060885c0sm711918c88.3.2025.11.13.11.14.40 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 13 Nov 2025 11:14:40 -0800 (PST) Date: Thu, 13 Nov 2025 11:14:38 -0800 From: "Vishal Moola (Oracle)" To: "Matthew Wilcox (Oracle)" Cc: Andrew Morton , David Hildenbrand , linux-mm@kvack.org, Will Deacon Subject: Re: [PATCH 1/4] mm: Use frozen pages for page tables Message-ID: References: <20251113140448.1814860-1-willy@infradead.org> <20251113140448.1814860-2-willy@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: C69A2A0016 X-Stat-Signature: dfis3er4xx69g6jf7ozdnrn1fbxwuas5 X-Rspam-User: X-HE-Tag: 1763061282-532488 X-HE-Meta: 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 1BGzujvy 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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 Thu, Nov 13, 2025 at 10:24:27AM -0800, Vishal Moola (Oracle) wrote: > On Thu, Nov 13, 2025 at 02:04:43PM +0000, Matthew Wilcox (Oracle) wrote: > > Page tables do not use the reference count. That means we can avoid While looking into the second patch, I came across this one instance in sparc32. Commit 1996d47a0db ("sparc32: mm: Only call ctor()/dtor() functions for first and last user") decided to start using the refcount for something. I'm not certain this code should even be using ptdescs, but theres a page_ptdesc() call in there for now :(. As far as I can tell, this is only a thing for sparc32. Cc-ing Will as the author of those commits. > > two atomic operations (one on alloc, one on free) by allocating frozen > > pages here. This does not interfere with compaction as page tables are > > non-movable allocations. > > > > pagetable_alloc() and pagetable_free() need to move out of line to make > > this work as alloc_frozen_page() and free_frozen_page() are not exported > > Nit: s/page/pages/g > > > outside the mm for now. We'll want them out of line anyway soon. > > > > Signed-off-by: Matthew Wilcox (Oracle) > > LGTM. > Reviewed-by: Vishal Moola (Oracle) So I guess I retract this for now...