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b=Qs5A9MTasyW/MZTWjl781rUA3+rm5IGMl3iJV9wo8sCOgpQQij+pQHJryBa+JNAud D2QW2QYqclrds4uDNw6HIJ2vaB8uXcbPQdaGyVluwUIjyDmWPEEqI9zc6G1LCuNFwY TttGY72hASAoBsL1ohRbrmPa33cscCuXZGpo/RyUv2iB5KXOcAUNLzVaaC2+kNwMyW 9xGSK+px3UXlLb62VshQPhR3lmXnfidxqltYElOpH+j9sHEPmjkMIoJp21+3II0/GM bwYWkRq46ZRwfPt77aWH9b6v8OreD70Rc4+no2li6Ui5xmYUl3sjYF5WhYTFQ+SnV7 s6I5DhLW1VJQg== Message-ID: <5987cdee-9174-44fb-8e2b-41e6ad969612@kernel.org> Date: Fri, 8 May 2026 22:54:58 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 3/4] mm: introduce bpf_mthp_ops struct ops To: Vernon Yang , akpm@linux-foundation.org, ljs@kernel.org, roman.gushchin@linux.dev, inwardvessel@gmail.com, shakeel.butt@linux.dev, ast@kernel.org, daniel@iogearbox.net, surenb@google.com Cc: tz2294@columbia.edu, baohua@kernel.org, lance.yang@linux.dev, dev.jain@arm.com, laoar.shao@gmail.com, gutierrez.asier@huawei-partners.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, bpf@vger.kernel.org, Vernon Yang References: <20260508150055.680136-1-vernon2gm@gmail.com> <20260508150055.680136-4-vernon2gm@gmail.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 3AB2DA0009 X-Rspam-User: X-Stat-Signature: dpqafk6168h3kenughdueqy5caz88hmi X-HE-Tag: 1778273708-874480 X-HE-Meta: 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 ocETQNxF iEwevLfGSIGIGzikIVbQysPOYJh41hW+OsZffkxaZTkgnDMrk/b/H6jZEnJYGpPOFulS1dgSgfuO9Bjygm4PGjVxq658W255W+nZpte4Bugg0E1J6lfW1P8lmpoy8B0WeKbE2Qct/haTJnVmyivxhLfBii/UiBGUOJ3wNyV6JSUSrCr5mNWzDIw2tEaw1qYGlaK4xqSSYiMQwVyur8tmNdCTXNBA9HqDT1+va3Lp0ib4gRBjVgOx238BZqRZ/EUR5y6ZqBaSpfkD/E+/H/8eUm2OcwhmGXnC9QnQhO7Trhvcxb3PiNptU8Bv63zgNgUgsOs8EodQ6vvqE1qzCOXe6JsqKh87uqK/2+t99KkCvhZ+LnUdPQ/CklBJniLFa2dhRIMhkUD5w1wHKIQsRuea1woiczDU7sc9QBV/aEITqd8gQJhCL2qZlwkI33g== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: > > #include /* only for vma_is_dax() */ > #include > @@ -296,6 +297,11 @@ unsigned long thp_vma_allowable_orders(struct vm_area_struct *vma, > enum tva_type type, > unsigned long orders) > { > + /* The eBPF-specified orders overrides which order is selected. */ > + orders &= bpf_mthp_choose(vma->vm_mm, orders); > + if (!orders) > + return 0; > + There was some discussion around this in the past: where should we hook into (e.g., deferred shrinker?), which information should we provide to the hook (e.g., vma properties?). We concluded mostly to "we don't know". I know that Rik van Riel wanted to look into doing this properly, but seems like he got distracted :) I assume there will be a lwn.net article covering the "BPF in MM" session we had at LSF/MM just this week. Conclusion: ABI stability is a headake. The simplistic approach of deciding an order for the whole MM is very likely not what we want. -- Cheers, David