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Sat, 24 Oct 2026 12:09:00 -0700 (PDT) Received: from localhost ([153.61.198.244]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-3adeba32e38sm3785610a91.2.2026.10.24.12.08.59 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 24 Oct 2026 12:08:59 -0700 (PDT) Content-Type: text/plain; charset=UTF-8 Date: Sat, 24 Oct 2026 19:08:59 +0000 Message-Id: To: "zhen.ni" , , , , , , , , , , , , , , , , , , Cc: , , , Subject: Re: [PATCH v3 0/7] mm/page_owner: add bpf_iter and kfuncs From: "Alexei Starovoitov" In-Reply-To: <06925440-8df8-4f2e-aea0-ede1a98435fa@easystack.cn> References: <20261021112437.1799213-1-zhen.ni@easystack.cn> <06925440-8df8-4f2e-aea0-ede1a98435fa@easystack.cn> X-Mailer: mkdraft (claude review draft; edit before sending) Content-Transfer-Encoding: 8bit X-Archived-By: MIME-Version: 1.0 X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 9623AC0005 X-Spam-Status: No, score=-2.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS autolearn=no autolearn_force=no version=4.0.1 X-Stat-Signature: s7qtampu5rp1guo177bc5ngfe5jc1u8i X-HE-Tag: 1792868941-241604 X-HE-Meta: U2FsdGVkX19l4LkDdeKothqgEjMQOwB1HNeB+w2QLPpWkwUmJCZmrtJPAmQLN4GODGhKX48VD43Ny1I8Hl+avicrZk60jD4qqXcQNzARMjw4VMEj3zv7e7lg+7QbW+HbcVgvvV0du46G+3T8v2Z1CJ8TaFTCTNnsHcjh9vtwHnVjCpZD6HCcPArnpWHhf0JiY0lkDP7P2L2ZJH4pOfvnNlu1PQjgPtaMkZL/MqDKl2gxFl0sEHj8gVS81av/FBlr0FXXkBqidXb+VAUSS/XkoyKFppazgoHKltJUG/XodTZpgZCdWvuphyMxSJpY9Q6T0T9Rk+449C6SB4zRLkcBVdYwYdzkzPlpH4UEumqbSGF5f0+HqYb2Sd7v6Qs4lncxff/lRESehv7751X7b4/KmAcS/agU/GpAoj6mjGwwuo8wM2rDtDDiJ7bTShijRyUK+uZ/itxaa138Uhf6hEPBnOrZvYnUGgiFUKzH55yoCmRnsPrss9np74jYnbA/lwc3UoX3mzJxCjwZav5QsY3eEFwTTrCDveq6EyqZVLlTnKd2J+2jplXxW/hHHLyltQ9BMTq6C8iCfu3KI+4nGJ7pjkPGp+vuKgT1izJ4srj1UfLIIRDsvjA0yocJrYfPF4eiLVL7/VsT2pc8qKHLUraZUzXbifQCHMi8Y1k7ZQwVcXc05m06Gp3/Y5hymsQl8TuxIbAYMsmGk+vMIatqWX/7DoD9uOp2VMBotM31gTrbJC6eyUGULyq97BaqdsVy2b452c/pOnjFuzoX9bCmi/AjPbo7QKQjfX1h3ybgiS5NVJxYTYeNy51vXHvrr7PF9USzfsia6p0ZULbjdTM8TDHKvrEfmnlA1r4YGSP5fhNKXBuZpd9vzQkKby0HHDVTxY4LyAMlHJT3Oqp/KozyXGh0eNwllw60lKvUx1KvLdrC1stE8iGIjK2AlIfIqgw4RP3o/+kv2G6tnEDSLlMJOH0 RLZvY/3v 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On Sat, Oct 24, 2026 at 10:19 AM zhen.ni wrote: > For this one node alone, about 97% of spanned is holes. With > bpf_for(pfn, start, end) plus a bpf_page_owner_read() per iteration, > that is at least 16,712,944 kfunc calls, and bpf_for has no scheduling > point inside, and all of them are wasted work. The gap grows with memory Right. spanned includes the holes. So don't pass them. /sys/devices/system/memory/ has memoryN only for present blocks. /sys/devices/system/node/nodeN/ links to the blocks of that node. /proc/iomem has "System RAM" ranges. 523024 pages in a 32G node looks like 64K pages. Then the whole 256G box is 4M pfns. When a hole is passed anyway the call ends at !online_section() in pfn_to_online_page(). /proc/kpageflags does that plus put_user() for every pfn, holes included. Syscall progs run under migrate_disable() only. > front. The spanned of this node is already 17.23M, so a single bpf_for > cannot cover it; you have to split it into N chunks and poll, with the > chunking state kept in a prog map, i.e. a loop nested in a loop. The loop over chunks is in user space. One bpf_prog_test_run_opts() per range with start and nr in ctx_in. No map, no nested loop. > for 52-bit PA. A 32-bit PFN range will overflow here. The snippet was: bpf_for(i, 0, ctx->nr) { pfn = ctx->start + i; i is an offset within the chunk. start and pfn are 64-bit. > Solving all of this requires yet another, more complex kfunc—and it > looks increasingly like bpf iter. So why not just use the iter? Nothing of the above needs kernel code. v3 is +474 -83 lines on the kernel side. The diff I sent is +55 -1 and it doesn't touch the debugfs path.