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Wed, 11 Dec 2024 08:38:59 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id cyCWLqNPWWdeOgAAD6G6ig (envelope-from ); Wed, 11 Dec 2024 08:38:59 +0000 Message-ID: Date: Wed, 11 Dec 2024 09:38:59 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH bpf-next v2 1/6] mm, bpf: Introduce __GFP_TRYLOCK for opportunistic page allocation Content-Language: en-US To: Alexei Starovoitov , Sebastian Andrzej Siewior Cc: bpf , Andrii Nakryiko , Kumar Kartikeya Dwivedi , Andrew Morton , Peter Zijlstra , Steven Rostedt , Hou Tao , Johannes Weiner , shakeel.butt@linux.dev, Michal Hocko , Matthew Wilcox , Thomas Gleixner , Tejun Heo , linux-mm , Kernel Team References: <20241210023936.46871-1-alexei.starovoitov@gmail.com> <20241210023936.46871-2-alexei.starovoitov@gmail.com> <20241210090136.DGfYLmeo@linutronix.de> From: Vlastimil Babka Autocrypt: addr=vbabka@suse.cz; keydata= xsFNBFZdmxYBEADsw/SiUSjB0dM+vSh95UkgcHjzEVBlby/Fg+g42O7LAEkCYXi/vvq31JTB KxRWDHX0R2tgpFDXHnzZcQywawu8eSq0LxzxFNYMvtB7sV1pxYwej2qx9B75qW2plBs+7+YB 87tMFA+u+L4Z5xAzIimfLD5EKC56kJ1CsXlM8S/LHcmdD9Ctkn3trYDNnat0eoAcfPIP2OZ+ 9oe9IF/R28zmh0ifLXyJQQz5ofdj4bPf8ecEW0rhcqHfTD8k4yK0xxt3xW+6Exqp9n9bydiy tcSAw/TahjW6yrA+6JhSBv1v2tIm+itQc073zjSX8OFL51qQVzRFr7H2UQG33lw2QrvHRXqD Ot7ViKam7v0Ho9wEWiQOOZlHItOOXFphWb2yq3nzrKe45oWoSgkxKb97MVsQ+q2SYjJRBBH4 8qKhphADYxkIP6yut/eaj9ImvRUZZRi0DTc8xfnvHGTjKbJzC2xpFcY0DQbZzuwsIZ8OPJCc LM4S7mT25NE5kUTG/TKQCk922vRdGVMoLA7dIQrgXnRXtyT61sg8PG4wcfOnuWf8577aXP1x 6mzw3/jh3F+oSBHb/GcLC7mvWreJifUL2gEdssGfXhGWBo6zLS3qhgtwjay0Jl+kza1lo+Cv BB2T79D4WGdDuVa4eOrQ02TxqGN7G0Biz5ZLRSFzQSQwLn8fbwARAQABzSBWbGFzdGltaWwg QmFia2EgPHZiYWJrYUBzdXNlLmN6PsLBlAQTAQoAPgIbAwULCQgHAwUVCgkICwUWAgMBAAIe AQIXgBYhBKlA1DSZLC6OmRA9UCJPp+fMgqZkBQJkBREIBQkRadznAAoJECJPp+fMgqZkNxIQ ALZRqwdUGzqL2aeSavbum/VF/+td+nZfuH0xeWiO2w8mG0+nPd5j9ujYeHcUP1edE7uQrjOC Gs9sm8+W1xYnbClMJTsXiAV88D2btFUdU1mCXURAL9wWZ8Jsmz5ZH2V6AUszvNezsS/VIT87 AmTtj31TLDGwdxaZTSYLwAOOOtyqafOEq+gJB30RxTRE3h3G1zpO7OM9K6ysLdAlwAGYWgJJ V4JqGsQ/lyEtxxFpUCjb5Pztp7cQxhlkil0oBYHkudiG8j1U3DG8iC6rnB4yJaLphKx57NuQ PIY0Bccg+r9gIQ4XeSK2PQhdXdy3UWBr913ZQ9AI2usid3s5vabo4iBvpJNFLgUmxFnr73SJ KsRh/2OBsg1XXF/wRQGBO9vRuJUAbnaIVcmGOUogdBVS9Sun/Sy4GNA++KtFZK95U7J417/J Hub2xV6Ehc7UGW6fIvIQmzJ3zaTEfuriU1P8ayfddrAgZb25JnOW7L1zdYL8rXiezOyYZ8Fm ZyXjzWdO0RpxcUEp6GsJr11Bc4F3aae9OZtwtLL/jxc7y6pUugB00PodgnQ6CMcfR/HjXlae h2VS3zl9+tQWHu6s1R58t5BuMS2FNA58wU/IazImc/ZQA+slDBfhRDGYlExjg19UXWe/gMcl De3P1kxYPgZdGE2eZpRLIbt+rYnqQKy8UxlszsBNBFsZNTUBCACfQfpSsWJZyi+SHoRdVyX5 J6rI7okc4+b571a7RXD5UhS9dlVRVVAtrU9ANSLqPTQKGVxHrqD39XSw8hxK61pw8p90pg4G /N3iuWEvyt+t0SxDDkClnGsDyRhlUyEWYFEoBrrCizbmahOUwqkJbNMfzj5Y7n7OIJOxNRkB IBOjPdF26dMP69BwePQao1M8Acrrex9sAHYjQGyVmReRjVEtv9iG4DoTsnIR3amKVk6si4Ea X/mrapJqSCcBUVYUFH8M7bsm4CSxier5ofy8jTEa/CfvkqpKThTMCQPNZKY7hke5qEq1CBk2 wxhX48ZrJEFf1v3NuV3OimgsF2odzieNABEBAAHCwXwEGAEKACYCGwwWIQSpQNQ0mSwujpkQ PVAiT6fnzIKmZAUCZAUSmwUJDK5EZgAKCRAiT6fnzIKmZOJGEACOKABgo9wJXsbWhGWYO7mD 8R8mUyJHqbvaz+yTLnvRwfe/VwafFfDMx5GYVYzMY9TWpA8psFTKTUIIQmx2scYsRBUwm5VI EurRWKqENcDRjyo+ol59j0FViYysjQQeobXBDDE31t5SBg++veI6tXfpco/UiKEsDswL1WAr tEAZaruo7254TyH+gydURl2wJuzo/aZ7Y7PpqaODbYv727Dvm5eX64HCyyAH0s6sOCyGF5/p eIhrOn24oBf67KtdAN3H9JoFNUVTYJc1VJU3R1JtVdgwEdr+NEciEfYl0O19VpLE/PZxP4wX PWnhf5WjdoNI1Xec+RcJ5p/pSel0jnvBX8L2cmniYnmI883NhtGZsEWj++wyKiS4NranDFlA HdDM3b4lUth1pTtABKQ1YuTvehj7EfoWD3bv9kuGZGPrAeFNiHPdOT7DaXKeHpW9homgtBxj 8aX/UkSvEGJKUEbFL9cVa5tzyialGkSiZJNkWgeHe+jEcfRT6pJZOJidSCdzvJpbdJmm+eED w9XOLH1IIWh7RURU7G1iOfEfmImFeC3cbbS73LQEFGe1urxvIH5K/7vX+FkNcr9ujwWuPE9b 1C2o4i/yZPLXIVy387EjA6GZMqvQUFuSTs/GeBcv0NjIQi8867H3uLjz+mQy63fAitsDwLmR EP+ylKVEKb0Q2A== In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 7CBF22000E X-Stat-Signature: stzxeo78pw1q4sth3jc1pess4eroh9nb X-Rspam-User: X-Rspamd-Server: rspam11 X-HE-Tag: 1733906331-501485 X-HE-Meta: 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 6484IQyN 13X1hUQIeoSxTct7AmNP283oAPJv8gHHlyyN90WSDoEv/f/OaW5lgMiVQUdHszfjhTH7jeRHUjUbDtdjuTGk1iNu+r2v6LHUT3HuvV1iNrAHE5eqgOHJNPr/LY9AFmJHiDiNJ1Df1fedrxUH+Yu1cBKPIHc5bCIyqM24zk/A44qcmAUjQY4FKLNA18IUpwuewvZS7XyQC1UDQnafH38TzBVd0lVxlouVUKg0gZ8+h8/KNqQ+33eT0zkSEpi4entfM06q3ihIAr3n1Ehg+tZDeF0UVRtsW1XYYGqq7Kcp1lAjkCiFOWbm0Nz1BrKO2sivmWe9WxZK9CsmmqTgaVe1d8TXnGCYSc/CbbVOsa0Wslsx7+BZIFN9x7UYO2yFZKc3vnXXa+hQ90LiUCG4WMdwARty4CcoeHCgqDGvb/pxK6Ycelv8g38H0Q8GzgH8gM+yei/ks58n1fmVZ7sI= 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 12/10/24 22:53, Alexei Starovoitov wrote: > On Tue, Dec 10, 2024 at 1:01 AM Sebastian Andrzej Siewior > wrote: >> >> On 2024-12-09 18:39:31 [-0800], Alexei Starovoitov wrote: >> > From: Alexei Starovoitov >> > >> > Tracing BPF programs execute from tracepoints and kprobes where running >> > context is unknown, but they need to request additional memory. >> > The prior workarounds were using pre-allocated memory and BPF specific >> > freelists to satisfy such allocation requests. Instead, introduce >> > __GFP_TRYLOCK flag that makes page allocator accessible from any context. >> > It relies on percpu free list of pages that rmqueue_pcplist() should be >> > able to pop the page from. If it fails (due to IRQ re-entrancy or list >> > being empty) then try_alloc_pages() attempts to spin_trylock zone->lock >> > and refill percpu freelist as normal. >> > BPF program may execute with IRQs disabled and zone->lock is sleeping in RT, >> > so trylock is the only option. >> >> The __GFP_TRYLOCK flag looks reasonable given the challenges for BPF >> where it is not known how much memory will be needed and what the >> calling context is. > > Exactly. > >> I hope it does not spread across the kernel where >> people do ATOMIC in preempt/ IRQ-off on PREEMPT_RT and then once they >> learn that this does not work, add this flag to the mix to make it work >> without spending some time on reworking it. > > We can call it __GFP_BPF to discourage any other usage, > but that seems like an odd "solution" to code review problem. Could we perhaps not expose the flag to public headers at all, and keep it only as an internal detail of try_alloc_pages_noprof()?