From: Christoph Hellwig <hch@lst.de>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
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 09:44:51 +0100 [thread overview]
Message-ID: <20221030084451.GA5278@lst.de> (raw)
In-Reply-To: <CAHk-=whyZ8NduHPYUGz6PdpVSo3fPtUB6rPu1-wG3u2G8wvCcQ@mail.gmail.com>
On Wed, Oct 26, 2022 at 10:46:46AM -0700, Linus Torvalds wrote:
> Seriously, non-cache coherent DMA in 2022 is a sign of an incompetent
> platform architect or hardware designer, and at some point I think
> that should just be called out for the incredible garbage it is.
It is garbage, but still incredibly common. And there is a simple
reason for that: it's cheap.
> I think we should just stop bending over backwards over this, and say
> "if your DMA isn't coherent, it's on your driver to mark its
> allocations".
Many of the allocations do not come from the driver. They can be
page cache, anonymous user memory, 17 layers of kernel "subsystems"
above the actual driver. And while the first two usuall won't have
size / alignment problems, the latter is where the real mess is.
next prev parent reply other threads:[~2022-10-30 8:44 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
2022-10-30 8:44 ` Christoph Hellwig [this message]
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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