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Tue, 10 Dec 2024 18:39:17 +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 t8dPO9WKWGd7ZQAAD6G6ig (envelope-from ); Tue, 10 Dec 2024 18:39:17 +0000 Message-ID: Date: Tue, 10 Dec 2024 19:39:17 +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 , bpf@vger.kernel.org Cc: andrii@kernel.org, memxor@gmail.com, akpm@linux-foundation.org, peterz@infradead.org, bigeasy@linutronix.de, rostedt@goodmis.org, houtao1@huawei.com, hannes@cmpxchg.org, shakeel.butt@linux.dev, mhocko@suse.com, willy@infradead.org, tglx@linutronix.de, tj@kernel.org, linux-mm@kvack.org, kernel-team@fb.com References: <20241210023936.46871-1-alexei.starovoitov@gmail.com> <20241210023936.46871-2-alexei.starovoitov@gmail.com> 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: <20241210023936.46871-2-alexei.starovoitov@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: A47561C000A X-Stat-Signature: eyzg3tapgag8111rjkotesjc7jo41bh3 X-Rspam-User: X-Rspamd-Server: rspam09 X-HE-Tag: 1733855936-810383 X-HE-Meta: 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 AqKM9OS7 sRSctDpeB1aBKTi4T91OnbG7/GtOiO2cydhGAHNkJck7d/JzH2TCrbl+JeUkBYG61NaSZT/QOWnc/euhGdT9w1QvfKXr5gfmT7DVXNFkpgwKaXv6zJvXnM/kNKrEUk7WKLDnO2em+QdYzT0WpjtAWNDPV+OH1jPJHT7sjxuucR0AZw9PIZIAmtPrNpoJhkWxX3Q9MlU1Yg2fF6GwP7LpF42A/1+NbVVMJMY6Oy7ipjp35np91sZ2rENEhDeNTVZVjXmgcgjSBaqMmmpjKcbDlAQeMeCfJDQQZTWO9kzSeEtiz+qKwif7PMuO9XKzjmDtjMpXmnCVdLcNTiJ4nlQYBqrnE8rG5GP19SXExcgN0JEvFQU4Z+d8TIIXvO/m5Qd0d14YNk4mm7tM9Lw4+2ep1WpnGhaQmzdSBC8RioQcU0svhUp67oNq5qUs02GPr7IAae+O0qNjIhuCu2g6R7819u6zsnk27k7lyx+icvbIcTePNamk= 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 03:39, 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. > In theory we can introduce percpu reentrance counter and increment it > every time spin_lock_irqsave(&zone->lock, flags) is used, > but we cannot rely on it. Even if this cpu is not in page_alloc path > the spin_lock_irqsave() is not safe, since BPF prog might be called > from tracepoint where preemption is disabled. So trylock only. > > Note, free_page and memcg are not taught about __GFP_TRYLOCK yet. > The support comes in the next patches. > > This is a first step towards supporting BPF requirements in SLUB > and getting rid of bpf_mem_alloc. > That goal was discussed at LSFMM: https://lwn.net/Articles/974138/ > > Signed-off-by: Alexei Starovoitov I think there might be more non-try spin_locks reachable from page allocations: - in reserve_highatomic_pageblock() which I think is reachable unless this is limited to order-0 - try_to_accept_memory_one() - as part of post_alloc_hook() in set_page_owner(), stack depot might do raw_spin_lock_irqsave(), is that one ok? hope I didn't miss anything else especially in those other debugging hooks (KASAN etc)