From: Christoph Hellwig <hch@lst.de>
To: Catalin Marinas <catalin.marinas@arm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Arnd Bergmann <arnd@arndb.de>, Will Deacon <will@kernel.org>,
Marc Zyngier <maz@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Herbert Xu <herbert@gondor.apana.org.au>,
Ard Biesheuvel <ardb@kernel.org>, Christoph Hellwig <hch@lst.de>,
Isaac Manjarres <isaacmanjarres@google.com>,
Saravana Kannan <saravanak@google.com>,
linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v2 2/2] treewide: Add the __GFP_PACKED flag to several non-DMA kmalloc() allocations
Date: Sun, 30 Oct 2022 09:46:02 +0100 [thread overview]
Message-ID: <20221030084602.GB5278@lst.de> (raw)
In-Reply-To: <Y1sGXFfPsRe8zzkB@arm.com>
On Thu, Oct 27, 2022 at 11:29:48PM +0100, Catalin Marinas wrote:
> The driver is not necessarily broken. The same small kmalloc() in a USB
> driver can work fine on a fully coherent platform but if that chip ends
> up on a SoC that doesn't support coherent DMA, it needs bigger kmalloc()
> alignment. The driver could check if it's coherent but that's more of an
> arch detail that the driver shouldn't care about. If we define a new API
> like dma_alloc() and drivers don't use it, that's when we can claim they
> are broken.
>
> A further optimisation would be for dma_alloc() to take a struct device
> pointer and check dev_is_dma_coherent() before deciding to align the
> size, though this doesn't work when the allocation place cannot tell the
> destination device (e.g. alloc_skb(), though these buffers are
> cacheline-aligned already).
The other thing would be to check the dma mask so that we don't end
up bounce buffering again.
next prev parent reply other threads:[~2022-10-30 8:46 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-25 20:52 [PATCH v2 0/2] mm: Allow kmalloc() allocations below ARCH_KMALLOC_MINALIGN Catalin Marinas
2022-10-25 20:52 ` [PATCH v2 1/2] mm: slab: Introduce __GFP_PACKED for smaller kmalloc() alignments Catalin Marinas
2022-10-26 6:39 ` Greg Kroah-Hartman
2022-10-26 8:39 ` Catalin Marinas
2022-10-26 9:49 ` Greg Kroah-Hartman
2022-10-26 9:58 ` Catalin Marinas
2022-10-27 12:11 ` Hyeonggon Yoo
2022-10-28 7:32 ` Catalin Marinas
2022-10-25 20:52 ` [PATCH v2 2/2] treewide: Add the __GFP_PACKED flag to several non-DMA kmalloc() allocations Catalin Marinas
2022-10-26 6:50 ` Greg Kroah-Hartman
2022-10-26 9:48 ` Catalin Marinas
2022-10-26 12:59 ` Greg Kroah-Hartman
2022-10-26 17:09 ` Catalin Marinas
2022-10-26 17:21 ` Greg Kroah-Hartman
2022-10-26 17:46 ` Linus Torvalds
2022-10-27 22:29 ` Catalin Marinas
2022-10-28 9:37 ` Greg Kroah-Hartman
2022-10-28 9:37 ` Greg Kroah-Hartman
2022-10-30 8:47 ` Christoph Hellwig
2022-10-30 9:02 ` Greg Kroah-Hartman
2022-10-30 9:13 ` Christoph Hellwig
2022-10-30 16:43 ` Catalin Marinas
2022-11-01 10:59 ` Christoph Hellwig
2022-11-01 17:19 ` Catalin Marinas
2022-11-01 17:24 ` Christoph Hellwig
2022-11-01 17:32 ` Catalin Marinas
2022-11-01 17:39 ` Christoph Hellwig
2022-11-01 19:10 ` Isaac Manjarres
2022-11-02 11:05 ` Catalin Marinas
2022-11-02 20:50 ` Isaac Manjarres
2022-11-01 18:14 ` Robin Murphy
2022-11-02 13:10 ` Catalin Marinas
2022-10-30 8:46 ` Christoph Hellwig [this message]
2022-10-30 8:44 ` Christoph Hellwig
2022-11-03 16:15 ` Vlastimil Babka
2022-11-03 18:03 ` Catalin Marinas
2022-10-26 6:54 ` [PATCH v2 0/2] mm: Allow kmalloc() allocations below ARCH_KMALLOC_MINALIGN Greg Kroah-Hartman
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