From: Christoph Hellwig <hch@lst.de>
To: Dave Hansen <dave.hansen@intel.com>
Cc: Georgi Djakov <quic_c_gdjako@quicinc.com>,
catalin.marinas@arm.com, will@kernel.org,
dave.hansen@linux.intel.com, luto@kernel.org,
peterz@infradead.org, tglx@linutronix.de, mingo@redhat.com,
bp@alien8.de, hpa@zytor.com, hch@lst.de,
m.szyprowski@samsung.com, robin.murphy@arm.com,
linux-arm-kernel@lists.infradead.org, iommu@lists.linux.dev,
linux-kernel@vger.kernel.org, djakov@kernel.org
Subject: Re: [RFC] mm: Allow ZONE_DMA32 to be disabled via kernel command line
Date: Fri, 27 Jan 2023 07:35:55 +0100 [thread overview]
Message-ID: <20230127063555.GA3300@lst.de> (raw)
In-Reply-To: <dca84e05-e376-c593-74fa-37c58f30767a@intel.com>
On Thu, Jan 26, 2023 at 10:51:17AM -0800, Dave Hansen wrote:
>
> Also, what are the practical implications here? There are obviously an
> ever decreasing number of 32-bit DMA devices out there. Somebody that
> has one and uses this option might be sad because now they're stuck
> using ZONE_DMA which is quite tiny.
>
> What other ZONE_DMA32 users are left? Will anyone else care? There is
> some DMA32 slab and vmalloc() functionality remaining. Is it impacted?
DMA32 never supported lab. But < 64-bit DMA device are unfortunately
still not uncommon, and configuring out ZONE_DMA32 breaks them pretty
badly as we guarantee that a DMA mask of 32-bit always works.
So I'm not only very much against this patch, but also the currently
existing way to configure out ZONE_DMA32 on arm64, which needs to
go away.
If people want ZONE_DMA32 to go away we need something to replace
it first, like a large enough CMA region in the 32-bit addressable
range.
next prev parent reply other threads:[~2023-01-27 6:36 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-26 16:43 [RFC] mm: Allow ZONE_DMA32 to be disabled via kernel command line Georgi Djakov
2023-01-26 18:51 ` Dave Hansen
2023-01-26 22:56 ` Georgi Djakov
2023-01-27 0:57 ` Randy Dunlap
2023-01-27 6:35 ` Christoph Hellwig [this message]
2023-01-27 6:52 ` H. Peter Anvin
2023-01-27 7:07 ` Christoph Hellwig
2023-01-26 19:15 ` Robin Murphy
2023-01-27 2:20 ` Chris Goldsworthy
[not found] ` <20230127085553.5120-1-hdanton@sina.com>
2023-02-01 4:09 ` Chris Goldsworthy
2023-01-30 5:26 ` kernel test robot
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