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Thu, 19 Mar 2026 10:38:35 -0700 (PDT) MIME-Version: 1.0 References: <20260319-gfp64-v1-0-2c73b8d42b7f@google.com> <215517e5-a49b-4eb7-824c-8c42e4db046e@kernel.org> In-Reply-To: <215517e5-a49b-4eb7-824c-8c42e4db046e@kernel.org> From: Brendan Jackman Date: Thu, 19 Mar 2026 18:38:23 +0100 X-Gm-Features: AaiRm51ReH28GS8eypWtXXz5qbVr-s5lM__ht0Ottf-Wh5rZqfZBVxcZKaXtLNg Message-ID: Subject: Re: [PATCH 0/5] mm: Switch gfp_t to unsigned long To: "Vlastimil Babka (SUSE)" Cc: Andrew Morton , Michal Hocko , David Rientjes , Shakeel Butt , Suren Baghdasaryan , Johannes Weiner , Zi Yan , Harry Yoo , Hao Li , Christoph Lameter , Roman Gushchin , Uladzislau Rezki , Matthew Wilcox , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Linus Torvalds Content-Type: text/plain; charset="UTF-8" X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 66EF2A000B X-Stat-Signature: 8xozhfxxuxry5w68airunhiqmhtjoxpf X-Rspam-User: X-HE-Tag: 1773941917-614716 X-HE-Meta: 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 ljRmODp8 PC3kqVPRk7/g1tmdNO3yq95xrCoIVhleRh0ZcDE6yzCMJ/gCbOP4jv5yi3kkgEd4cruvjOXNfaGqsbn545ETWtC9tuJc35MLpEmOzkF4vzO14ORMI76o1Mrp8pxXqaKAe+kPjnsvzjqbITjKrclxBp2dEThViTFhVyyie5I3kBTHV0TbyfbPqol9nxFktooyeL7xLjrdGqtABf7TtSpO4XK/lbu3hCFQqORKHnedRv3xJq4RsCAdauySfzyOzit/EB+sAZzyqTsVAQ7SiF7LUCae+RXiUXekKP3wvNg4TMNkJ/3NhQ/JbqzGOWrxbXaLW6ipw+c++CPwIp/5F820ex/ZQRLaRfTLg3wzr Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, 19 Mar 2026 at 18:03, Vlastimil Babka (SUSE) wrote: > > On 3/19/26 17:03, Brendan Jackman wrote: > > As pointed out by Vlastimil in [0], my proposal for __GFP_UNMAPPED is > > probably not needed for 32-bit. This offers a way out of the GFP flag > > scarcity so in preparation for this, flip gfp_t to be 64-bit on 64-bit > > machines, while leaving it 32-bit on 32-bit machines. > > Thanks for tackling this! But now I'm wondering, if we decide to change it, > would it be worth trying to add some type safety too? To help with cases > like the recent kmalloc_objs() footgun discussed in this comment thread > https://lwn.net/Articles/1063356/ Do you mean something similar to pgprot_t? I did that in [0] but I'm rather sheepish about it, I only went for it because I think it's especially needed for the specific "type" due to the migration path creating a high type-unsafety risk. And that was totally local to a few files in mm/. Are there common issues with gfp_t in particular besides the kmalloc_objs() thing? If so then maybe it could make sense. It's not a problem I've ever run into myself though. [0] https://lore.kernel.org/all/20260225-page_alloc-unmapped-v1-8-e8808a03cd66@google.com/