From: Christoph Hellwig <hch@infradead.org>
To: Tyrel Datwyler <tyreld@linux.vnet.ibm.com>
Cc: james.bottomley@hansenpartnership.com,
martin.petersen@oracle.com, linux-scsi@vger.kernel.org,
stable@vger.kernel.org, Christoph Hellwig <hch@infradead.org>,
brking@linux.vnet.ibm.com, linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH] ibmvscsi: use GFP_ATOMIC with dma_alloc_coherent in map_sg_data
Date: Fri, 11 Jan 2019 10:27:28 -0800 [thread overview]
Message-ID: <20190111182728.GB5469@infradead.org> (raw)
In-Reply-To: <4c5a470e-fa98-1ffd-7f55-5a4ffb3a692a@linux.vnet.ibm.com>
On Thu, Jan 10, 2019 at 03:15:35PM -0800, Tyrel Datwyler wrote:
> On a secondary note I was unaware of the GFP_ATOMIC limitations. Should this be
> added to the documentation somewhere? I don't see any mention here form
> DMA-API-HOWTO.txt.
The DMA documentation unfortauntely doesn't seem very good. It's been
on my todo list to eventually update it, but I'm still discoverying
various warts.
GFP_ATOMIC allocations generally work fine on DMA coherent
architectures, but tend to cause problems on a lot of non-coherent
ones with the notable exceptions of arm and arm64 that go to great
length to introduce special pools for them. But that code is rarely
exercised, so I found various bugs e.g. in the arm64 iommu code for
this case.
But more importantly there really should be no need for the coherent
allocation from irq context - we only need coherent for descriptors
that don't have clear ownership, and aything allocated in the I/O path
generally has that.
prev parent reply other threads:[~2019-01-11 18:29 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-10 2:58 [PATCH] ibmvscsi: use GFP_ATOMIC with dma_alloc_coherent in map_sg_data Tyrel Datwyler
2019-01-10 14:56 ` Brian King
2019-01-10 15:07 ` Christoph Hellwig
2019-01-10 20:11 ` Tyrel Datwyler
2019-01-11 18:24 ` Christoph Hellwig
2019-01-10 23:15 ` Tyrel Datwyler
2019-01-11 18:27 ` Christoph Hellwig [this message]
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