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From: Catalin Marinas <catalin.marinas@arm.com>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Mark Rutland <mark.rutland@arm.com>,
	Will Deacon <will@kernel.org>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	Android Kernel Team <kernel-team@android.com>,
	Ard Biesheuvel <ardb@kernel.org>,
	Vincent Whitchurch <vincent.whitchurch@axis.com>
Subject: Re: [PATCH] arm64: cache: Lower ARCH_DMA_MINALIGN to 64 (L1_CACHE_BYTES)
Date: Tue, 1 Jun 2021 11:14:08 +0100	[thread overview]
Message-ID: <20210601101408.GA29312@arm.com> (raw)
In-Reply-To: <CAK8P3a286UUquL701GEu4P32yXdKsNccoMCdKdcs=ySSjOFyEg@mail.gmail.com>

On Fri, May 28, 2021 at 11:35:32AM +0200, Arnd Bergmann wrote:
> On Thu, May 27, 2021 at 3:19 PM Mark Rutland <mark.rutland@arm.com> wrote:
> > > More recently, it has been reported that a ARCH_DMA_MINALIGN of 128
> > > bytes wastes considerable memory (~6% immediately after boot on one
> > > system).
> > >
> > > Reduce ARCH_DMA_MINALIGN to 64 bytes and allow the warning/taint to
> > > indicate if there are machines that unknowingly rely on this.
> >
> > The rationale above makes sense to me, so:
> >
> > Acked-by: Mark Rutland <mark.rutland@arm.com>
> 
> I think it would make sense to go even further than this in the
> future, and allow
> setting a smaller minimum alignment depending what hardware is detected
> at boot time.

Yeah, we talked about this in the past. The problem is that very early
the kernel doesn't know whether it'll have devices that require
non-coherent DMA. So we'd probably need to start with a 64 byte
ARCH_DMA_MINALIGN and populate the slab caches slightly later once the
kernel learns more about the system it's running on.

-- 
Catalin

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  reply	other threads:[~2021-06-01 10:15 UTC|newest]

Thread overview: 46+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-27 12:43 [PATCH] arm64: cache: Lower ARCH_DMA_MINALIGN to 64 (L1_CACHE_BYTES) Will Deacon
2021-05-27 13:11 ` Catalin Marinas
2021-05-27 13:19 ` Mark Rutland
2021-05-28  9:35   ` Arnd Bergmann
2021-06-01 10:14     ` Catalin Marinas [this message]
2021-05-31  5:38 ` Ard Biesheuvel
2021-06-01 18:21 ` Will Deacon
     [not found] ` <CGME20210602132541eucas1p17127696041c26c00d1d2f50bef9cfaf0@eucas1p1.samsung.com>
2021-06-02 13:25   ` Marek Szyprowski
2021-06-02 13:51     ` Mark Rutland
2021-06-02 14:09       ` Marek Szyprowski
2021-06-02 14:14         ` Arnd Bergmann
2021-06-02 14:28           ` Marek Szyprowski
2021-06-02 14:52             ` Arnd Bergmann
2021-06-07 12:17               ` Arnd Bergmann
2021-06-04 10:01         ` Mark Rutland
2021-06-07  9:58           ` Marek Szyprowski
2021-06-07 12:01             ` Mark Rutland
2021-06-07 13:08               ` Mark Rutland
2021-06-07 13:39                 ` Will Deacon
2021-06-07 13:56                   ` Mark Rutland
2021-06-07 13:57                   ` Arnd Bergmann
2021-06-07 15:17                     ` Maxime Ripard
2021-06-07 15:50                       ` Arnd Bergmann
2021-06-08  8:57                         ` Mark Rutland
2021-06-07 15:32                     ` Mark Rutland
2021-06-02 14:11       ` Arnd Bergmann
2021-06-02 14:15         ` Marek Szyprowski
     [not found] ` <uHgsRacR8hJ7nW-I-pIcehzg-lNIn7NJvaL7bP9tfAftFsBjsgaY2qTjG9zyBgxHkjNL1WPNrD7YVv2JVD2_Wy-a5VTbcq-1xEi8ZnwrXBo=@protonmail.com>
2021-07-06 10:26   ` Catalin Marinas
2021-07-06 13:29     ` Robin Murphy
2021-07-06 13:33       ` Will Deacon
2021-07-06 13:44         ` Marc Zyngier
2021-07-06 14:21           ` Robin Murphy
2021-07-06 14:30           ` Arnd Bergmann
2021-07-06 14:46             ` Marc Zyngier
2021-07-06 15:43               ` Arnd Bergmann
2021-07-06 17:15                 ` Yassine Oudjana
2021-07-06 20:33                   ` Arnd Bergmann
2021-07-06 22:27                     ` Bjorn Andersson
2021-07-07  9:27                       ` Will Deacon
2021-07-07  8:24                     ` Yassine Oudjana
2021-07-07  9:29                       ` Arnd Bergmann
2021-07-07 14:41                         ` Jeffrey Hugo
2021-07-08 20:59                           ` Jeffrey Hugo
2021-07-09  8:48                             ` Will Deacon
2021-07-09 17:10                               ` Catalin Marinas
2021-07-06 16:20             ` Will Deacon

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