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b=m8IjRoXAb3Zn/Q67ROj1HfcvutqDAL5M5RN5U9jIQ+MDQtwlLUhEPBHAM0gg0+vj9 bRhMmk2R0w2Ss7XmKPV75OZiSRABwamNdgK+i03w9BnRUcRL3LCL1GmYUC8HUaPbBx 714XFx4wuYbiYxYvymJiZ/pvn7ebpp77eClZHB4OTicuQh5dnxYWf7MM3aw4ABy+8+ 4jqy5YMbhMooeiEtIzOtsjS5NFA0qeEHUfuYJSBl2KV54Nqc64SzKPBwRx/PWyIYQr 0PgZMICX0rP0hpEsD3wqrCOGaxgXneNtmubvl0+jiBUZUGTnmhTPT7ULd+qB9BhQMw UlXfQKFEJVS9w== Message-ID: <6ff14b27-a494-4faa-94ed-ebbf63116125@kernel.org> Date: Thu, 19 Mar 2026 20:58:34 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 0/5] mm: Switch gfp_t to unsigned long Content-Language: en-US To: Brendan Jackman 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 References: <20260319-gfp64-v1-0-2c73b8d42b7f@google.com> <215517e5-a49b-4eb7-824c-8c42e4db046e@kernel.org> From: "Vlastimil Babka (SUSE)" In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 4B61CA0013 X-Stat-Signature: xoaknjptr6ufujkj7d9qqxqeg1rjwwef X-Rspam-User: X-HE-Tag: 1773950321-507824 X-HE-Meta: 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 0Yqmxs2c 1nCQxrx5WlvJj+oPZidKOvg14MJowRTF/uxaZipNARIgtn0RZFhDafJZbhNhFWbPlOW/0BYBJom2u6CJsLmhkz0bahbtMOVv4l8GoOWMTDahcYh/Z3jWWHihXTfZHiFK5H5itnOoqgPYjdoRgkQiAYE8b89hDcELRfqPgtxk6oKsXfA9JmHFXkJIJL3ZCbdJ83sSo5OOPmwLPBPUDoTEBYXtRkwXEPQNsUOMivatYSv+/xOryEatIhYI7XGMFG6hGNZb/IgrHWhnhCXuqZmnKeP2xp3BW3bxXyvy0OHGFZyaxeKifBjUmiyO0+nhRcdY7wU1ITOPvT86vBAhGL7FODZnNnn7rUmh9cgwcPSUVo3XO569/dY0siNCfMA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 3/19/26 18:38, Brendan Jackman wrote: > 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? Yeah, at least I don't know a better way. > I did that in [0] but I'm rather sheepish about it, I only went for it Right. > 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. I think it's a hazard in any case where there are multiple arguments to a function where one is gfp flags and other some integer, and somebody gets the order wrong. But I just verified that at least in the kmalloc_objs() mistake, sparse will flag it, thanks to the __bitwise annotation. Would be better if compiler did, but it makes the case for changing gfp_t smaller if it was too disruptive (it likely would be). > [0] https://lore.kernel.org/all/20260225-page_alloc-unmapped-v1-8-e8808a03cd66@google.com/