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Message-ID: <20230720065216.GB4395@lst.de>
Date: Thu, 20 Jul 2023 08:52:16 +0200
From: Christoph Hellwig <hch@....de>
To: Petr Tesarik <petrtesarik@...weicloud.com>
Cc: Stefano Stabellini <sstabellini@...nel.org>,
Russell King <linux@...linux.org.uk>,
Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
Dave Hansen <dave.hansen@...ux.intel.com>,
"maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
"H. Peter Anvin" <hpa@...or.com>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
"Rafael J. Wysocki" <rafael@...nel.org>,
Juergen Gross <jgross@...e.com>,
Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
Christoph Hellwig <hch@....de>,
Marek Szyprowski <m.szyprowski@...sung.com>,
Robin Murphy <robin.murphy@....com>,
Petr Tesarik <petr.tesarik.ext@...wei.com>,
Jonathan Corbet <corbet@....net>,
Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
Hans de Goede <hdegoede@...hat.com>,
James Seo <james@...iv.tech>,
James Clark <james.clark@....com>,
Kees Cook <keescook@...omium.org>,
"moderated list:XEN HYPERVISOR ARM" <xen-devel@...ts.xenproject.org>,
"moderated list:ARM PORT" <linux-arm-kernel@...ts.infradead.org>,
open list <linux-kernel@...r.kernel.org>,
"open list:MIPS" <linux-mips@...r.kernel.org>,
"open list:XEN SWIOTLB SUBSYSTEM" <iommu@...ts.linux.dev>,
Roberto Sassu <roberto.sassu@...weicloud.com>,
Kefeng Wang <wangkefeng.wang@...wei.com>, petr@...arici.cz
Subject: Re: [PATCH v4 0/8] Allow dynamic allocation of software IO TLB
bounce buffers
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.
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