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Date: Mon, 14 Oct 2024 17:14:06 -0700
From: Jakub Kicinski <kuba@kernel.org>
To: Yunsheng Lin <linyunsheng@huawei.com>
Cc: <davem@davemloft.net>, <pabeni@redhat.com>, <liuyonglong@huawei.com>,
 <fanghaiqing@huawei.com>, <zhangkun09@huawei.com>, Alexander Lobakin
 <aleksander.lobakin@intel.com>, Robin Murphy <robin.murphy@arm.com>,
 Alexander Duyck <alexander.duyck@gmail.com>, IOMMU <iommu@lists.linux.dev>,
 Alexei Starovoitov <ast@kernel.org>, Daniel Borkmann
 <daniel@iogearbox.net>, Jesper Dangaard Brouer <hawk@kernel.org>, John
 Fastabend <john.fastabend@gmail.com>, Matthias Brugger
 <matthias.bgg@gmail.com>, AngeloGioacchino Del Regno
 <angelogioacchino.delregno@collabora.com>, <netdev@vger.kernel.org>,
 <intel-wired-lan@lists.osuosl.org>, <bpf@vger.kernel.org>,
 <linux-kernel@vger.kernel.org>, <linux-arm-kernel@lists.infradead.org>,
 <linux-mediatek@lists.infradead.org>
Subject: Re: [PATCH net v2 0/2] fix two bugs related to page_pool
Message-ID: <20241014171406.43e730c9@kernel.org>
In-Reply-To: <b1fd5ece-b967-4e56-ad4f-64ec437e2634@huawei.com>
References: <20240925075707.3970187-1-linyunsheng@huawei.com>
	<b1fd5ece-b967-4e56-ad4f-64ec437e2634@huawei.com>
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On Sat, 12 Oct 2024 20:05:31 +0800 Yunsheng Lin wrote:
> 1. Semantics changing of supporting unlimited inflight pages
>    to limited inflight pages that are as large as the pool_size
>    of page_pool.

How can this possibly work?

The main thing stopping me from reposting my fix that it'd be nice to
figure out if a real IOMMU device is bound or not. If we don't have
real per-device mappings we presumably don't have to wait. If we can 
check this condition we are guaranteed not to introduce regressions,
since we would be replacing a crash by a wait, which is strictly better.

If we'd need to fiddle with too many internals to find out if we have
to wait - let's just always wait and see if anyone complains.