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b=oUy4Hb5+/P8MX/PrlvRLQVq8G2rjpxqY9PXgxaJx8GMWTufvB36jG2M//fkYsl3vw tF2XSVIwtNHSP1rfDrvKvjU8ASrWo9oTvrCOmk69sEm+vSSn9Jfn60GqytYviA3fur E/0/TrwbHZe6gQxqDQWFE99h53YiQYuhap7EQqE+L543eA/Ji9/xC//wZR5heo25Kj HC8J08N1mMcPoiMNpiob9oJXsFSGAiSUJ0byFR+1bZuyUKweQJCl3po0dK12XTfShP 0tQnXYuNv+IqS7zZYSPpAVASYn0HPUClCemJ5HevF29fArmGQvk6qT3eVCWGS2U3qR P7hwWo9eP+NDg== Message-ID: Date: Fri, 20 Mar 2026 11:02:55 +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 , Matthew Wilcox 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 , linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <20260319-gfp64-v1-0-2c73b8d42b7f@google.com> From: "Vlastimil Babka (SUSE)" In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 1F87D140005 X-Stat-Signature: 1dczxwk4g8i9ks4bqxtboxfuam9cdngt X-Rspam-User: X-HE-Tag: 1774000980-345135 X-HE-Meta: U2FsdGVkX19nomTGvQLdK0x2IY/WIHZYn1uGrodRtui9okcd79zN8PgpbdLX0tW3cWI6Ejf9FtNGSzEyFJ0Mo4kLmoe6Ro5rVBL5LuNEmQ7Nxgz0pkGKkm51Lax5Nva7bY27nHXCxECAUBX83aF4X17xOwUsHHN9HxIi7CwuieQBPUtZ+5vbJsjmrOA8V7rWB/H0MZpYuhLCgggWAVu50i0dKrxQNtR9gZ9sqGrE7M4FWmShpu0TA5lCYdpUdRLl9FTcnJntMQxhlT7tl9ZLRZIjyEsO3s6KRk4PUsAQQ4RLXFT65ruEPUWfReEH49E4TEuVKRzKyoEnuSghIU/2q6Y2bDaLFTNxKDMxjuR3YXpWk2YTnOZO51yzfTUoFSJoiymD6D3AiJlLpfru+9meQyE1E5uVXXdg6LEUc1X68fiwMdSH+3l1OQw9hnJf1BoyGVx8qcvX1muLpKYmRFKCe/b0lw75LpP5Oq1VHgOFWR/bHSCCa2JQHLjLdquzJ5vEpTkAS7rCxweUnkih8E8BzUlurOunAF2nimZxnKs84Z8NJXFuoJBfgLlLVby0I0nQJbes0FS600QZgS1QGx3x0zEjwUOBTJMPKBz6stUaB0SBYm9c7Ihxfs75cIWGaMfpsIqj0K8BCtip3B6PxovUkjs6mQE5jH1GGvwneRvwYgl1FJQGBRK9IplZJ3sdicHtLUHFbtFU6bnmQcSxUSWCXqviQxoua1L9pMM8vvur2x6PSkY4Pm0THPtOWr8c1GV8T4cJyccfByVDm509rYvvW//CaWQVoMRefb7C7TCpPctsD0XI9VVycougzds5ERXL+Soz6HGBjoB3pmn5rIOsusYvEBkBJnrStUscZ54VyBr4qXo4/xK28J5wHs721TpI6gzmvi/W6Is7qQjaXuB0u2t+W9SzC5SM76CKoS/7J36cZYQBBuhTFlT1h01oH6mDSLTTgyvvjE8rqOUdu4Q aLtLUggg Qu1Nrr6/8UP4Oow30vxeU8ziefLx5nVcExdXD3nJpTylQtOgJ0JabjmZETGOiRK8ckNYvRCPQeINc7l4ooA3NuuwVF1+waxTpjhNtRmkOmlnBEdtLuOXrMzqBdZmybV62hJ5SOLyBWkTkB0SJZKiyEWoVOQtXvj47qjoE384aP1Z6QCa4b9MTKNOhuLYZa55XupqbxiaO/LCmlp5AsOmv46ncgBwhYNZ3h9pTrSbGpqK0qKYKWSoHFMJ9pwnlpZYmR1s79zNd8JCavPl541iwrCXtD+EHU/HNumJfCJNm6ZQqdydR9oPAzSUYrw== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 3/20/26 10:48, Brendan Jackman wrote: > On Thu Mar 19, 2026 at 9:39 PM UTC, Matthew Wilcox wrote: >> On Thu, Mar 19, 2026 at 06:40:59PM +0000, Brendan Jackman wrote: >>> I will paste the diff at the bottom. I _think_ all the problematic >>> expansions are downstream of struct xarray, but it's quite likely my >>> sense for problematic struct expansions is weak. >> >> Urgh, no, it's not all xarray. There's one in address_space which we're >> trying to shrink, not grow. > > Oh sorry I just assumed that one was xa_flags. > >> There's one in struct sock too. > > Huh, I suspect I am embarassing myself with this question, but why are > we sensitive to the size of struct sock? It's currently 784 bytes in my > build. Are the adjacent fields very hot, and we need to look up the GFP > flags from hot paths? > >> I don't think this idea is worth it. There are other projects of greater >> or lesser churniess which will give us some flags back. For example, >> we could finish the GFP_NOFS and GFP_NOIO removal. We could finish the >> radix_tree -> XArray removal and get back three bits. That's five bits >> without even starting new projects, just finishing old ones. > > Anyway, this also makes sense. But, Vlastimil, I guess you had an > ulterior motive for this suggestion? Partially. After seeing various issues with kmalloc_nolock() relying on lack of __GFP_KSWAPD_RECLAIM to indicate the nolock, it would be great to just add another gfp flag for it, but with only few left, I didn't dare. But I'll admit it wasn't well thought idea out wrt consequences. Sorry that nobody shot it down before you actually tried to implement it.