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[100.36.248.188]) by smtp.gmail.com with ESMTPSA id d75a77b69052e-5148e7bf7e4sm94051171cf.17.2026.05.11.09.52.11 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 11 May 2026 09:52:12 -0700 (PDT) Date: Mon, 11 May 2026 12:52:10 -0400 From: Gregory Price To: "Michael S. Tsirkin" Cc: linux-kernel@vger.kernel.org, "David Hildenbrand (Arm)" , Jason Wang , Xuan Zhuo , Eugenio =?iso-8859-1?Q?P=E9rez?= , Muchun Song , Oscar Salvador , Andrew Morton , Lorenzo Stoakes , "Liam R. 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Howlett" , Harry Yoo , Hao Li Subject: Re: [PATCH resend v6 03/30] mm: thread user_addr through page allocator for cache-friendly zeroing Message-ID: References: <9b53972f4854c1064b92cefc464f51949afeb83f.1778489843.git.mst@redhat.com> <20260511114853-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260511114853-mutt-send-email-mst@kernel.org> X-Rspam-User: X-Rspamd-Queue-Id: 2DC36A0010 X-Rspamd-Server: rspam06 X-Stat-Signature: jd8ff5qowseamdeixb5kqsowszpbqtkg X-HE-Tag: 1778518334-811557 X-HE-Meta: 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 /KwGyKsu 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, May 11, 2026 at 11:55:40AM -0400, Michael S. Tsirkin wrote: > On Mon, May 11, 2026 at 11:37:37AM -0400, Gregory Price wrote: > > On Mon, May 11, 2026 at 05:01:55AM -0400, Michael S. Tsirkin wrote: > > > > > +/* > > > + * Sentinel for user_addr: indicates a non-user allocation. > > > + * Cannot use 0 because address 0 is a valid userspace mapping. > > > + */ > > > +#define USER_ADDR_NONE ((unsigned long)-1) > > > > Ehm, hm. Does -1 hold as a non-user address across all architectures? > > > > What about in linear addressing / no VM mode? > > this is used on a fault. I don't think there are any faults then? > But maybe FAULT_ADDR_NONE would be clearer. > Meh, naming here is less relevant than the sentinel correctness. My only concern is really whether -1 could end up being a valid address in some horrid future timeline and this all going belly up. Is why I asked about whether this is correct on all architectures. > > So the trade off is: > > a) churn the current interface for everyone > > b) add a user_ variant and know people will just get it wrong > > I was also explicitly asked not to proliferate too many new APIs. > Yeah simply spelling it out, not asking for a change. Probably no better way to go about it. ~Gregory