linux-kernel - Re: [PATCH v1 0/2] swiotlb: Fix a couple of bugs in sizing areas

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Message-ID: <20230626160725.5164ca74@meshulam.tesarici.cz>
Date:   Mon, 26 Jun 2023 16:07:25 +0200
From:   Petr Tesařík <petr@...arici.cz>
To:     Petr Tesarik <petrtesarik@...weicloud.com>
Cc:     Christoph Hellwig <hch@....de>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>,
        iommu@...ts.linux.dev (open list:DMA MAPPING HELPERS),
        linux-kernel@...r.kernel.org (open list),
        Roberto Sassu <roberto.sassu@...weicloud.com>,
        Kefeng Wang <wangkefeng.wang@...wei.com>
Subject: Re: [PATCH v1 0/2] swiotlb: Fix a couple of bugs in sizing areas

On Mon, 26 Jun 2023 15:01:02 +0200
Petr Tesarik <petrtesarik@...weicloud.com> wrote:

> From: Petr Tesarik <petr.tesarik.ext@...wei.com>
> 
> While reworking the dynamic SWIOTLB implementation, I ran into some
> locking issues with the current implementation. I believe the bugs
> are serious enough to be fixed separately.

As an aside (and not directly related to the bugfixes themselves), I
wonder why the area size cannot be always equal to IO_TLB_SEGSIZE. Of
course, we would (usually) end up with more areas, but that should be
a good thing, shouldn't it? The area structure is quite small, so it
cannot be because of memory consumption concerns. The overhead of
taking an uncontended spinlock should also be negligible.

Do I miss something important here?

Petr T