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Date:   Thu, 20 Jul 2023 08:52:16 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Petr Tesarik <petrtesarik@huaweicloud.com>
Cc:     Stefano Stabellini <sstabellini@kernel.org>,
        Russell King <linux@armlinux.org.uk>,
        Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
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        Petr Tesarik <petr.tesarik.ext@huawei.com>,
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        Roberto Sassu <roberto.sassu@huaweicloud.com>,
        Kefeng Wang <wangkefeng.wang@huawei.com>, petr@tesarici.cz
Subject: Re: [PATCH v4 0/8] Allow dynamic allocation of software IO TLB
 bounce buffers
Message-ID: <20230720065216.GB4395@lst.de>
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Just to add a highlevel comment here after I feel like I need a little
more time to review the guts.

I'm still pretty concerned about the extra list that needs to be
consulted in is_swiotlb_buffer, but I can't really think of
anything better.  Maybe an xarray has better cache characteristics,
but that one requires even more allocations in the low-level dma map
path.

One thing I'd like to see for the next version is to make the
new growing code a config option at least for now.  It is a pretty
big change of the existing swiotlb behavior, and I want people to opt
into it conciously.  Maybe we can drop the option again after a few
years once everything has settled.