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Message-ID: <87ednxbr3c.fsf@toke.dk> Date: Wed, 03 May 2023 13:18:47 +0200 From: Toke Høiland-Jørgensen <toke@...hat.com> To: Jakub Kicinski <kuba@...nel.org>, Jesper Dangaard Brouer <brouer@...hat.com> Cc: Ilias Apalodimas <ilias.apalodimas@...aro.org>, netdev@...r.kernel.org, Eric Dumazet <eric.dumazet@...il.com>, linux-mm@...ck.org, Mel Gorman <mgorman@...hsingularity.net>, lorenzo@...nel.org, linyunsheng@...wei.com, bpf@...r.kernel.org, "David S. Miller" <davem@...emloft.net>, Paolo Abeni <pabeni@...hat.com>, Andrew Morton <akpm@...ux-foundation.org>, willy@...radead.org Subject: Re: [PATCH RFC net-next/mm V3 1/2] page_pool: Remove workqueue in new shutdown scheme Jakub Kicinski <kuba@...nel.org> writes: > On Fri, 28 Apr 2023 18:16:19 +0200 Jesper Dangaard Brouer wrote: >> This removes the workqueue scheme that periodically tests when >> inflight reach zero such that page_pool memory can be freed. >> >> This change adds code to fast-path free checking for a shutdown flags >> bit after returning PP pages. > > We can remove the warning without removing the entire delayed freeing > scheme. I definitely like the SHUTDOWN flag and patch 2 but I'm a bit > less clear on why the complexity of datapath freeing is justified. > Can you explain? You mean just let the workqueue keep rescheduling itself every minute for the (potentially) hours that skbs will stick around? Seems a bit wasteful, doesn't it? :) We did see an issue where creating and tearing down lots of page pools in a short period of time caused significant slowdowns due to the workqueue mechanism. Lots being "thousands per second". This is possible using the live packet mode of bpf_prog_run() for XDP, which will setup and destroy a page pool for each syscall... -Toke
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