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[109.81.16.57]) by smtp.gmail.com with UTF8SMTPSA id ffacd0b85a97d-426e50ef821sm12670523f8f.38.2025.10.14.23.21.22 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 14 Oct 2025 23:21:22 -0700 (PDT) Date: Wed, 15 Oct 2025 08:21:21 +0200 From: Michal Hocko To: Shakeel Butt Cc: Vlastimil Babka , Barry Song <21cnbao@gmail.com>, netdev@vger.kernel.org, linux-mm@kvack.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, Barry Song , Jonathan Corbet , Eric Dumazet , Kuniyuki Iwashima , Paolo Abeni , Willem de Bruijn , "David S. Miller" , Jakub Kicinski , Simon Horman , Suren Baghdasaryan , Brendan Jackman , Johannes Weiner , Zi Yan , Yunsheng Lin , Huacai Zhou , Alexei Starovoitov , Harry Yoo , David Hildenbrand , Matthew Wilcox , Roman Gushchin Subject: Re: [RFC PATCH] mm: net: disable kswapd for high-order network buffer allocation Message-ID: References: <20251013101636.69220-1-21cnbao@gmail.com> <927bcdf7-1283-4ddd-bd5e-d2e399b26f7d@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Stat-Signature: febahd6gkwzro6q1qze8o8eukphco11t X-Rspamd-Queue-Id: 841CB40005 X-Rspamd-Server: rspam09 X-HE-Tag: 1760509284-97039 X-HE-Meta: U2FsdGVkX1+rSdD1di8yCRXKsCGtmRde69yGA3D5BFUemQj+HPNn0eLl1V6msHf0jzKEOWKiGct2ieIhTdpBPGUialSKOKWrXAQkxlFfLmeWV1zxEbqHCzjXfVg/oyI7D4xpNV2FyBO7TP1tirm6a8ZaOdiRcumwr0Bwt/OgnsKjNBKuXaCdFnixEE5lu5p8f4PfyV/R1Shk9NAKdxVsQg/WwsGEr660DFdDA+2Q4flue9Lbo1CCEJfAeEQBfGav4465qoXmdOmO3keZdlzMVvnCQIun/M118KCc6BEJdU7ilVrYypg2GacNPTXIEr7Lt8ia8dYTvJEbpth9ECmaU5sRPR8Zzg3lot2kw5LHjLGNuo0dRUedL3tglpbZMthV0fkXN7GsPqaBsAs8ab7T8N0kxe9jcJslMBlGlBILbLHMn34LvLqkBiSxXx3i9CzE61kMCqHMpPOYPP4Tm5uWhYmZk47jFY6j/Onw9P8WjIgJwY2qB7CY1R+Rh4aEAI0YB8qNV06qS+Bt/x0reK6CtibipOzIHk9LyPAWb6k9Pft1VNFfEa6Ju2QT6kDdgye1wWxyE71mjQS6IkoHUqd3yX91/AIQ+VkIh9c84MfiWeaKKfdxPol4ewL7pTagTMcudkavtekhMvdJdY4oOCuw9wrjG10Uw0vQrgcSOMWMdeskUD21bu8+XJ+yjh/Dc/856PZBlk1Ja/boQhKTpL8HTvkqrBrBGSMPweXEM4oPzg2ru8W4uo3MozHrRteWfvOJ4K7w5x8M99ktOxr3uZjACeEy1xYg/ryYWWk4rnE3WEp93fdq4+TDaAJKU7RhEbZFuowiHTk004IEoTb4DVjkL0+IazmfYmveFz+Unf35q1ssqmH1SJ6MGGVlQHw5//EbX/1ztPKmRLnEzrVY+EFH7dHy7+VRWsj/swwPRELbAnJzLKr0MRO44Xs7OP0IWQLRcoDMYN3g/HRJ/RLN9A/ Lc2gmCXd D+urpm7B7q0TkzKWMg6lWdk6weYUDPul5Sx6mGTCtrfjYno6TZDCVmWtUCP0CiMVpx+U3nGWLUZ2G/W7kAguiklCo41pN05x4Z86vWYt8BUE7OCYSr+HmpP4SsQkmfgPM/P1SWiZAuSu72/9q12aakWseuurERTAzlNlPyMYN+q4FlJBloaoSV0U7VxJ6yCaclgMlwFiWQfLy9CV/QTOsC9av6zgfexwleI9ljfF/ZvlCuMHC41qPYjwoSKogdLA9cZzgZhkvVpW8tjoeVg7fazJtmJ5iHjtqvyzVvTWPspK+IBmY/Jx7+XoDqS0eUZcQKUm0/ZZB9pmNavmgPYh118BmloENkcrRjKE03qURRBFMpREM8RNLISKDHJrMKUYkpxY7VyGQwKt7fBP2lHC4DyRQGBDUpRX4prqA 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 Tue 14-10-25 10:22:03, Shakeel Butt wrote: > On Tue, Oct 14, 2025 at 05:14:47PM +0200, Michal Hocko wrote: > > On Tue 14-10-25 07:27:06, Shakeel Butt wrote: > > > On Tue, Oct 14, 2025 at 09:26:49AM +0200, Michal Hocko wrote: > > > > On Mon 13-10-25 20:30:13, Vlastimil Babka wrote: > > > > > On 10/13/25 12:16, Barry Song wrote: > > > > > > From: Barry Song > > > > [...] > > > > > I wonder if we should either: > > > > > > > > > > 1) sacrifice a new __GFP flag specifically for "!allow_spin" case to > > > > > determine it precisely. > > > > > > > > As said in other reply I do not think this is a good fit for this > > > > specific case as it is all or nothing approach. Soon enough we discover > > > > that "no effort to reclaim/compact" hurts other usecases. So I do not > > > > think we need a dedicated flag for this specific case. We need a way to > > > > tell kswapd/kcompactd how much to try instead. > > > > > > To me this new floag is to decouple two orthogonal requests i.e. no lock > > > semantic and don't wakeup kswapd. At the moment the lack of kswapd gfp > > > flag convey the semantics of no lock. This can lead to unintended usage > > > of no lock semantics by users which for whatever reason don't want to > > > wakeup kswapd. > > > > I would argue that callers should have no business into saying whether > > the MM should wake up kswapd or not. The flag name currently suggests > > that but that is mostly for historic reasons. A random page allocator > > user shouldn't really care about this low level detail, really. > > I agree but unless we somehow enforce/warn for such cases, there will be > users doing this. A simple grep shows kmsan is doing this. I worry there > might be users who are manually setting up gfp flags for their > allocations and not providing kswapd flag explicitly. Finding such cases > with grep is not easy. You are right but this is inherent problem of our gfp interface. It is too late to have a defensive interface I am afraid. -- Michal Hocko SUSE Labs