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Date: Tue, 2 May 2023 19:33:09 -0700
From: Jakub Kicinski <kuba@kernel.org>
To: Jesper Dangaard Brouer <brouer@redhat.com>
Cc: Ilias Apalodimas <ilias.apalodimas@linaro.org>, netdev@vger.kernel.org,
 Eric Dumazet <eric.dumazet@gmail.com>, linux-mm@kvack.org, Mel Gorman
 <mgorman@techsingularity.net>, lorenzo@kernel.org, Toke =?UTF-8?B?SMO4?=
 =?UTF-8?B?aWxhbmQtSsO4cmdlbnNlbg==?= <toke@redhat.com>,
 linyunsheng@huawei.com, bpf@vger.kernel.org, "David S. Miller"
 <davem@davemloft.net>, Paolo Abeni <pabeni@redhat.com>, Andrew Morton
 <akpm@linux-foundation.org>, willy@infradead.org
Subject: Re: [PATCH RFC net-next/mm V3 1/2] page_pool: Remove workqueue in
 new shutdown scheme
Message-ID: <20230502193309.382af41e@kernel.org>
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	<168269857929.2191653.13267688321246766547.stgit@firesoul>
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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?

> Performance is very important for PP, as the fast path is used for
> XDP_DROP use-cases where NIC drivers recycle PP pages directly into PP
> alloc cache.
> 
> This patch (since V3) shows zero impact on this fast path. Micro
> benchmarked with [1] on Intel CPU E5-1650 @3.60GHz. The slight code
> reorg of likely() are deliberate.