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Thu, 16 Jan 2025 08:31:11 +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 XhzwKM/DiGcmHgAAD6G6ig (envelope-from ); Thu, 16 Jan 2025 08:31:11 +0000 Message-ID: <478b027a-ef5b-4ed7-9fe3-ad2b627111ef@suse.cz> Date: Thu, 16 Jan 2025 09:31:10 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH bpf-next v5 2/7] mm, bpf: Introduce free_pages_nolock() To: Alexei Starovoitov Cc: bpf , Andrii Nakryiko , Kumar Kartikeya Dwivedi , Andrew Morton , Peter Zijlstra , Sebastian Sewior , Steven Rostedt , Hou Tao , Johannes Weiner , Shakeel Butt , Michal Hocko , Matthew Wilcox , Thomas Gleixner , Jann Horn , Tejun Heo , linux-mm , Kernel Team References: <20250115021746.34691-1-alexei.starovoitov@gmail.com> <20250115021746.34691-3-alexei.starovoitov@gmail.com> Content-Language: en-US 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-Action: no action X-Rspamd-Queue-Id: 022BBC000E X-Stat-Signature: rrpy46qh4ornpnhtsu5pbbx6qitg9cou X-Rspamd-Server: rspam08 X-Rspam-User: X-HE-Tag: 1737016274-66935 X-HE-Meta: U2FsdGVkX1+95HzukNrmatwyx4eXWebVpptihCWhDFZuT5fLDjC6l9VeIOlYEsrVKEgPT+Q51EBGYNiwA3MvPx3ECXckhj+ImT+TrkOxWSXXOHl+hLgEe4WEq9OUMdVcr2Wv4Yf0Pu92HOlv4qGCnhDeqSDv2I21mdWWoRNo8XhtnJKBn0ngOgLT1+CwGwy/C24xxS/K1fISgjttNBczPg8ChJfgbAiD7rKbrvBfTFx78sBdBqkT/xi+qU6jb/5OzUf1jWijDklHeoWTGHfHlzIOU98CP8h6DyweTAYW5PeIhcf9qrjM0wUiaHxBItjRT4hwLiuJyB//oXSv44fMI8ExE75wcAcJUY93QgLETtEyhPI+npKL5V5o3kij6bHF0JOxZdXGqRv47TXrXgHF3+YbPI6kyriRz4jhgYvqArTZ51z6biziDZktacYiZ/37+BQf+XlPKqQDxFKBrSGMU+7z/XQDO+uEyQO7qbeCNeIdr1cmXmmg3guSgJkVOC7YWiEGZnjwg5MRSG+jelvg1DuJ0xRtoYktSkOZJzTLuyn1witCJiihgME0KzTYH/ee7dbiPQhU49CKrGIyBntHnvXQFDAubVBFQtBd/OPCIUke8mHVBv4eXqt9XRoXa9aaHkYAITA6q6ZsIh0TWcWbAas/cFW79/j4vpjemBQqPInK2OSywVeY/VhEwsXoS0h833+DHOxwTwod01bBo8XVwKTwMXIwzIbP4o2zX4imEK4WaCnswnNeFhRMG2+qjYexj35JT3FoyXedEKckviEIkK3FaXi/45yk3EA1Br/Tib7FZRTvdyQmNmkA74OOSh2kanZWqqVPzPF+4yjijHId3y/tI0LbEOMVg5aKCetLEolg0ejJMUXEeROJQS/V0F7xCQ4mOCxNhP9Io2X1Uc8W+BIFakN40fEJQKtFhO4Mcl+VxJYu9sLYD8yDE0tiNj9ujKwbisBtC54iWyTvg6r gjTPZapo GOwAGUllvnGVj+OjhWDlKpsFgMAlhaYs+2c8ypvT8T9E3/+AMOJO13R3zOWsrc58psx53+HRnNBC6I031AzD5m0gOX5TIvlrzq8RPgnyp383IWYTJ21n9BTnQjna4AxWDHBiJZEmb9ZJhNu+BK8+RAeH4RHJC6hTHGBoVu1D3529l1AFVtvR+GOfRu106Q9FTSL+jlYn4zVrHjKevLz0C9YaqA8j9AWMFd3RQKSDFYIed5PhGY1fP+58u/267aVKNdElnRRo3u2Zh4CI0gC/Osg6nwa9Jc6KvK2yWRN9I1caIzzaLyR4ptkBkRtl4l80LWj2pSP1BAAITfgrAyLAmr23/YTCOSuWrSBhBDw2jK3eans1rO0lIdpbd/D7AZ3cwkB3pBoFKteqJTAn7KdC7+1ygePu11q70PCWNBoerEIYhpNAYKB+dPeGAsJ+uyKC8fhYW6D0uh3N/D5d0j7URQgRqnu3D4jFILIjhUU7Fa0uCX/8= 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 1/16/25 00:15, Alexei Starovoitov wrote: > On Wed, Jan 15, 2025 at 3:47 AM Vlastimil Babka wrote: >> >> On 1/15/25 03:17, Alexei Starovoitov wrote: >> > From: Alexei Starovoitov >> > >> > Introduce free_pages_nolock() that can free pages without taking locks. >> > It relies on trylock and can be called from any context. >> > Since spin_trylock() cannot be used in RT from hard IRQ or NMI >> > it uses lockless link list to stash the pages which will be freed >> > by subsequent free_pages() from good context. >> > >> > Do not use llist unconditionally. BPF maps continuously >> > allocate/free, so we cannot unconditionally delay the freeing to >> > llist. When the memory becomes free make it available to the >> > kernel and BPF users right away if possible, and fallback to >> > llist as the last resort. >> > >> > Signed-off-by: Alexei Starovoitov >> >> Acked-by: Vlastimil Babka >> >> With: >> >> > @@ -4853,6 +4905,17 @@ void __free_pages(struct page *page, unsigned int order) >> > } >> > EXPORT_SYMBOL(__free_pages); >> > >> > +/* >> > + * Can be called while holding raw_spin_lock or from IRQ and NMI, >> > + * but only for pages that came from try_alloc_pages(): >> > + * order <= 3, !folio, etc >> >> I think order > 3 is fine, as !pcp_allowed_order() case is handled too? > > try_alloc_page() has: > if (!pcp_allowed_order(order)) > return NULL; Ah ok I missed that the comment describes what pages try_alloc_pages() produces, not what's accepted here. > to make sure it tries pcp first. > bpf has no use for order > 1. Even 3 is overkill, > but it's kinda free to support order <= 3, so why not. > >> And >> what does "!folio" mean? > > That's what we discussed last year. > __free_pages() has all the extra stuff if (!head) and > support for dropping ref on the middle page. > !folio captures this more broadly. Aha! But in that case I realize we're actually wrong. It needs to be a folio (compound page) if it's order > 0 in order to drop that tricky !head freeing code. It's order > 0 pages that are not compound, that are problematic and should be eventually removed from the kernel. The solution is to add __GFP_COMP in try_alloc_pages_noprof(). This will have no effect on order-0 pages that BPF uses. Instead of "!folio" the comment could then say "compound".