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From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: Catalin Marinas <catalin.marinas@arm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.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 1/2] mm: slab: Introduce __GFP_PACKED for smaller kmalloc() alignments
Date: Wed, 26 Oct 2022 08:39:04 +0200	[thread overview]
Message-ID: <Y1jWCCd2Kkcrk0W/@kroah.com> (raw)
In-Reply-To: <20221025205247.3264568-2-catalin.marinas@arm.com>

On Tue, Oct 25, 2022 at 09:52:46PM +0100, Catalin Marinas wrote:
> By default kmalloc() returns objects aligned to ARCH_KMALLOC_MINALIGN.
> This can be somewhat large on architectures defining ARCH_DMA_MINALIGN
> (e.g. 128 on arm64) and significant memory is wasted through small
> kmalloc() allocations.
> 
> Reduce the minimum alignment for kmalloc() to the default
> KMALLOC_MIN_SIZE (8 for slub, 32 for slab) but align the
> requested size to the bigger ARCH_KMALLOC_MINALIGN unless a newly added
> __GFP_PACKED flag is passed. With this gfp flag, the alignment is
> reduced to KMALLOC_PACKED_ALIGN, at least sizeof(unsigned long long).

Can memory allocated with __GFP_PACKED be sent to DMA controllers?

If not, you should say that somewhere here or I'm going to get a bunch
of patches trying to add this flag to tiny USB urb allocations (where we
allocate 8 or 16 bytes) that is then going to fail on some hardware.

thanks,

greg k-h

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WARNING: multiple messages have this Message-ID (diff)
From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: Catalin Marinas <catalin.marinas@arm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.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 1/2] mm: slab: Introduce __GFP_PACKED for smaller kmalloc() alignments
Date: Wed, 26 Oct 2022 08:39:04 +0200	[thread overview]
Message-ID: <Y1jWCCd2Kkcrk0W/@kroah.com> (raw)
In-Reply-To: <20221025205247.3264568-2-catalin.marinas@arm.com>

On Tue, Oct 25, 2022 at 09:52:46PM +0100, Catalin Marinas wrote:
> By default kmalloc() returns objects aligned to ARCH_KMALLOC_MINALIGN.
> This can be somewhat large on architectures defining ARCH_DMA_MINALIGN
> (e.g. 128 on arm64) and significant memory is wasted through small
> kmalloc() allocations.
> 
> Reduce the minimum alignment for kmalloc() to the default
> KMALLOC_MIN_SIZE (8 for slub, 32 for slab) but align the
> requested size to the bigger ARCH_KMALLOC_MINALIGN unless a newly added
> __GFP_PACKED flag is passed. With this gfp flag, the alignment is
> reduced to KMALLOC_PACKED_ALIGN, at least sizeof(unsigned long long).

Can memory allocated with __GFP_PACKED be sent to DMA controllers?

If not, you should say that somewhere here or I'm going to get a bunch
of patches trying to add this flag to tiny USB urb allocations (where we
allocate 8 or 16 bytes) that is then going to fail on some hardware.

thanks,

greg k-h


  reply	other threads:[~2022-10-26  6:39 UTC|newest]

Thread overview: 74+ 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 ` Catalin Marinas
2022-10-25 20:52 ` [PATCH v2 1/2] mm: slab: Introduce __GFP_PACKED for smaller kmalloc() alignments Catalin Marinas
2022-10-25 20:52   ` Catalin Marinas
2022-10-26  6:39   ` Greg Kroah-Hartman [this message]
2022-10-26  6:39     ` Greg Kroah-Hartman
2022-10-26  8:39     ` Catalin Marinas
2022-10-26  8:39       ` Catalin Marinas
2022-10-26  9:49       ` Greg Kroah-Hartman
2022-10-26  9:49         ` Greg Kroah-Hartman
2022-10-26  9:58         ` Catalin Marinas
2022-10-26  9:58           ` Catalin Marinas
2022-10-27 12:11   ` Hyeonggon Yoo
2022-10-27 12:11     ` Hyeonggon Yoo
2022-10-28  7:32     ` Catalin Marinas
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
2022-10-25 20:52   ` Catalin Marinas
2022-10-26  6:50   ` Greg Kroah-Hartman
2022-10-26  6:50     ` Greg Kroah-Hartman
2022-10-26  9:48     ` Catalin Marinas
2022-10-26  9:48       ` Catalin Marinas
2022-10-26 12:59       ` Greg Kroah-Hartman
2022-10-26 12:59         ` Greg Kroah-Hartman
2022-10-26 17:09         ` Catalin Marinas
2022-10-26 17:09           ` Catalin Marinas
2022-10-26 17:21           ` Greg Kroah-Hartman
2022-10-26 17:21             ` Greg Kroah-Hartman
2022-10-26 17:46       ` Linus Torvalds
2022-10-26 17:46         ` Linus Torvalds
2022-10-27 22:29         ` Catalin Marinas
2022-10-27 22:29           ` Catalin Marinas
2022-10-28  9:37           ` Greg Kroah-Hartman
2022-10-28  9:37             ` Greg Kroah-Hartman
2022-10-28  9:37             ` Greg Kroah-Hartman
2022-10-28  9:37               ` Greg Kroah-Hartman
2022-10-30  8:47               ` Christoph Hellwig
2022-10-30  8:47                 ` Christoph Hellwig
2022-10-30  9:02                 ` Greg Kroah-Hartman
2022-10-30  9:02                   ` Greg Kroah-Hartman
2022-10-30  9:13                   ` Christoph Hellwig
2022-10-30  9:13                     ` Christoph Hellwig
2022-10-30 16:43                     ` Catalin Marinas
2022-10-30 16:43                       ` Catalin Marinas
2022-11-01 10:59                       ` Christoph Hellwig
2022-11-01 10:59                         ` Christoph Hellwig
2022-11-01 17:19                         ` Catalin Marinas
2022-11-01 17:19                           ` Catalin Marinas
2022-11-01 17:24                           ` Christoph Hellwig
2022-11-01 17:24                             ` Christoph Hellwig
2022-11-01 17:32                             ` Catalin Marinas
2022-11-01 17:32                               ` Catalin Marinas
2022-11-01 17:39                               ` Christoph Hellwig
2022-11-01 17:39                                 ` Christoph Hellwig
2022-11-01 19:10                                 ` Isaac Manjarres
2022-11-01 19:10                                   ` Isaac Manjarres
2022-11-02 11:05                                   ` Catalin Marinas
2022-11-02 11:05                                     ` Catalin Marinas
2022-11-02 20:50                                     ` Isaac Manjarres
2022-11-02 20:50                                       ` Isaac Manjarres
2022-11-01 18:14                           ` Robin Murphy
2022-11-01 18:14                             ` Robin Murphy
2022-11-02 13:10                             ` Catalin Marinas
2022-11-02 13:10                               ` Catalin Marinas
2022-10-30  8:46           ` Christoph Hellwig
2022-10-30  8:46             ` Christoph Hellwig
2022-10-30  8:44         ` Christoph Hellwig
2022-10-30  8:44           ` Christoph Hellwig
2022-11-03 16:15       ` Vlastimil Babka
2022-11-03 16:15         ` Vlastimil Babka
2022-11-03 18:03         ` Catalin Marinas
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
2022-10-26  6:54   ` Greg Kroah-Hartman

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