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Date:   Mon, 6 Nov 2023 08:44:48 +0100
From:   Christoph Hellwig <hch@lst.de>
To:     Petr =?utf-8?B?VGVzYcWZw61r?= <petr@tesarici.cz>
Cc:     Niklas Schnelle <schnelle@linux.ibm.com>,
        Christoph Hellwig <hch@lst.de>,
        Bjorn Helgaas <bhelgaas@google.com>,
        Marek Szyprowski <m.szyprowski@samsung.com>,
        Robin Murphy <robin.murphy@arm.com>,
        Petr Tesarik <petr.tesarik1@huawei-partners.com>,
        Ross Lagerwall <ross.lagerwall@citrix.com>,
        linux-pci <linux-pci@vger.kernel.org>,
        linux-kernel@vger.kernel.org, iommu@lists.linux.dev,
        Matthew Rosato <mjrosato@linux.ibm.com>,
        Halil Pasic <pasic@linux.ibm.com>
Subject: Re: Memory corruption with CONFIG_SWIOTLB_DYNAMIC=y
Message-ID: <20231106074448.GB17777@lst.de>
References: <104a8c8fedffd1ff8a2890983e2ec1c26bff6810.camel@linux.ibm.com> <20231103195949.0af884d0@meshulam.tesarici.cz>
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On Fri, Nov 03, 2023 at 07:59:49PM +0100, Petr Tesařík wrote:
> I don't think it's possible to improve the allocation logic without
> modifying the page allocator and/or the DMA atomic pool allocator to
> take additional constraints into account.
> 
> I had a wild idea back in March, but it would require some intrusive
> changes in the mm subsystem. Among other things, it would make memory
> zones obsolete. I mean, people may actually like to get rid of DMA,
> DMA32 and NORMAL, but you see how many nasty bugs were introduced even
> by a relatively small change in SWIOTLB. Replacing memory zones with a
> system based on generic physical allocation constraints would probably
> blow up the universe. ;-)

It would be very nice, at least for DMA32 or the 30/31-bit DMA pools
used on some architectures.  For the x86-style 16MB zone DMA I suspect
just having a small pool on the side that's not even exposed to the
memory allocator would probably work better.

I think a lot of the MM folks would love to be able to kill of the
extra zones.