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X-Proofpoint-ORIG-GUID: -ZVIab4R7aJt2g47nOTaBmk256hsQy2f X-Proofpoint-GUID: -ZVIab4R7aJt2g47nOTaBmk256hsQy2f X-Rspamd-Queue-Id: 2053C1A000E X-Rspam-User: X-Rspamd-Server: rspam07 X-Stat-Signature: zcg5ewo5pu5cb1dxq1wiukonaegp85yp X-HE-Tag: 1733236277-284046 X-HE-Meta: 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 Tg3UySJT 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 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 03/12/2024 12:06, Michal Hocko wrote: > On Mon 02-12-24 14:50:49, Frank van der Linden wrote: >> On Mon, Dec 2, 2024 at 1:58 PM Mateusz Guzik wrote: >>> Any games with "background zeroing" are notoriously crappy and I would >>> argue one should exhaust other avenues before going there -- at the end >>> of the day the cost of zeroing will have to get paid. >> >> I understand that the concept of background prezeroing has been, and >> will be, met with some resistance. But, do you have any specific >> concerns with the patch I posted? It's pretty well isolated from the >> rest of the code, and optional. > > The biggest concern I have is that the overhead is payed by everybody on > the system - it is considered to be a system overhead regardless only > part of the workload benefits from hugetlb pages. In other words the > workload using those pages is not accounted for the use completely. > > If the startup latency is a real problem is there a way to workaround > that in the userspace by preallocating hugetlb pages ahead of time > before those VMs are launched and hand over already pre-allocated pages? It should be relatively simple to actually do this. Me and Mike had experimented ourselves a couple years back but we never had the chance to send it over. IIRC if we: - add the PageZeroed tracking bit when a page is zeroed - clear it in the write (fixup/non-fixup) fault-path [somewhat similar to this series I suspect] Then what's left is to change the lookup of free hugetlb pages (dequeue_hugetlb_folio_node_exact() I think) to search first for non-zeroed pages. Provided we don't track its 'cleared' state, there's no UAPI change in behaviour. A daemon can just allocate/mmap+touch/etc them with read-only and free them back 'as zeroed' to implement a userspace scrubber. And in principle existing apps should see no difference. The amount of changes is consequently significantly smaller (or it looked as such in a quick PoC years back). Something extra on the top would perhaps be the ability so select a lookup heuristic such that we can pick the search method of non-zero-first/only-nonzero/zeroed pages behind ioctl() (or a better generic UAPI) to allow a scrubber to easily coexist with hugepage user (e.g. a VMM, etc) without too much of a dance. Joao