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gkmwi7dwoat7w1xcrwu4m1k6i4e39on3 X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: A5846140008 X-Rspam-User: X-HE-Tag: 1746860472-349346 X-HE-Meta: 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 lE1QF4/T T55QWygxKXfL92TN74V1CsBBjg1r9jT4NEUvwGzHwC6TP1kph0KyGMm+ihC9gPhPsVS0VJfLtRMPPMuo= 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 Fri, May 09, 2025 at 08:11:55PM -0700, Shakeel Butt wrote: > Hi Andrew, > > On Fri, May 09, 2025 at 06:26:32PM -0700, Andrew Morton wrote: > > On Fri, 9 May 2025 16:28:55 -0700 Shakeel Butt wrote: > > > > > BPF programs can trigger memcg charged kernel allocations in nmi > > > context. However memcg charging infra for kernel memory is not equipped > > > to handle nmi context. This series adds support for kernel memory > > > charging for nmi context. > > > > The patchset adds quite a bit of material to core MM on behalf of a > > single caller. So can we please take a close look at why BPF is doing > > this? > > > > What would be involved in changing BPF to avoid doing this, or of > > changing BPF to handle things locally? What would be the end-user > > impact of such an alteration? IOW, what is the value to our users of > > the present BPF behavior? > > > > Before answering the questions, let me clarify that this series is > continuation of the work which added similar support for page allocator > and related memcg charging and now the work is happening for > kmalloc/slab allocations. Alexei has a proposal on reentrant kmalloc and > here I am providing how memcg charging for that (reentrant kmalloc) > should work. > > Next let me take a stab in answering the questions and BPF folks can > correct me if I am wrong. From what I understand, users can attach BPF > programs at almost any place in kernel and those BPF programs can do > memory allocations. This line of work is to make those allocations work > if the any such BPF attach point is triggered in mni context. > > Before this line of work (reentrant page and slab allocators), I think > BPF had its internal cache but it was very limited and can easily fail > allocation requests (please BPF folks correct me if I am wrong). This > was discussed in LSFMM this year as well. > > Now regarding the impact to the users. First there will not be any > negative impact on the non-users of this feature. For the value this > feature will provide to users, I think this line of work will make BPF > programs of the users more reliable with better allocation behavior. > BPF folks, please add more comments for the value of these features. If kmalloc gains NMI-context support, preallocation would no longer be necessary, eliminating its memory overhead which has been observed to reach up to 1.5GB in Meta's fleet [1]. [1] https://lore.kernel.org/linux-mm/20250327145159.99799-1-alexei.starovoitov@gmail.com -- Cheers, Harry / Hyeonggon