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From: Catalin Marinas <catalin.marinas@arm.com>
To: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Cc: Will Deacon <will@kernel.org>, Marc Zyngier <maz@kernel.org>,
	Arnd Bergmann <arnd@arndb.de>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 08/10] mm/slab: Allow dynamic kmalloc() minimum alignment
Date: Thu, 7 Apr 2022 10:35:04 +0100	[thread overview]
Message-ID: <Yk6wSNz38Bv1lrmB@arm.com> (raw)
In-Reply-To: <Yk6sWNBSwNRbLdfZ@hyeyoo>

On Thu, Apr 07, 2022 at 06:18:16PM +0900, Hyeonggon Yoo wrote:
> On Thu, Apr 07, 2022 at 09:50:23AM +0100, Catalin Marinas wrote:
> > On Thu, Apr 07, 2022 at 03:46:37AM +0000, Hyeonggon Yoo wrote:
> > > On Tue, Apr 05, 2022 at 02:57:56PM +0100, Catalin Marinas wrote:
> > > > --- a/mm/slab_common.c
> > > > +++ b/mm/slab_common.c
> > > > @@ -838,9 +838,18 @@ void __init setup_kmalloc_cache_index_table(void)
> > > >  	}
> > > >  }
> > > >  
> > > > -static void __init
> > > > +unsigned int __weak arch_kmalloc_minalign(void)
> > > > +{
> > > > +	return ARCH_KMALLOC_MINALIGN;
> > > > +}
> > > > +
> > > 
> > > As ARCH_KMALLOC_ALIGN and arch_kmalloc_minalign() may not be same after
> > > patch 10, I think s/ARCH_KMALLOC_ALIGN/arch_kmalloc_minalign/g
> > > for every user of it would be more correct?
> > 
> > Not if the code currently using ARCH_KMALLOC_MINALIGN needs a constant.
> > Yes, there probably are a few places where the code can cope with a
> > dynamic arch_kmalloc_minalign() but there are two other cases where a
> > constant is needed:
> > 
> > 1. As a BUILD_BUG check because the code is storing some flags in the
> >    bottom bits of a pointer. A smaller ARCH_KMALLOC_MINALIGN works just
> >    fine here.
> > 
> > 2. As a static alignment for DMA requirements. That's where the newly
> >    exposed ARCH_DMA_MINALIGN should be used.
> > 
> > Note that this series doesn't make the situation any worse than before
> > since ARCH_DMA_MINALIGN stays at 128 bytes for arm64. Current users can
> > evolve to use a dynamic alignment in future patches. My main aim with
> > this series is to be able to create kmalloc-64 caches on arm64.
> 
> AFAIK there are bunch of drivers that directly calls kmalloc().

Well, lots of drivers call kmalloc() ;).

> It becomes tricky when e.g.) a driver allocates just 32 bytes,
> but architecture requires it to be 128-byte aligned.

That's the current behaviour, a 32 byte allocation would return an
object from kmalloc-128. I want to reduce this to at least kmalloc-64
(or smaller) if the CPU/SoC allows it.

> That's why everything allocated from kmalloc() need to be aligned in
> ARCH_DMA_MINALIGN.

I don't get your conclusion here. Would you mind explaining?

> So I'm yet skeptical on decoupling ARCH_DMA/KMALLOC_MINALIGN. Instead
> of decoupling it, I'm more into dynamically decreasing it.

The reason for decoupling is mostly that there are some static uses of
ARCH_KMALLOC_MINALIGN as per point 1 above. The other is the
__assume_kmalloc_alignment attribute. We shouldn't have such assumed
alignment larger than what a dynamic kmalloc() would return. To me it
makes a lot more sense for ARCH_KMALLOC_MINALIGN to be the minimum
guaranteed in a kernel build but kmalloc() returning a larger alignment
at run-time than the other way around.

Thanks.

-- 
Catalin

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  reply	other threads:[~2022-04-07  9:55 UTC|newest]

Thread overview: 140+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-04-05 13:57 [PATCH 00/10] mm, arm64: Reduce ARCH_KMALLOC_MINALIGN below the cache line size Catalin Marinas
2022-04-05 13:57 ` [PATCH 01/10] mm/slab: Decouple ARCH_KMALLOC_MINALIGN from ARCH_DMA_MINALIGN Catalin Marinas
2022-04-05 23:59   ` Hyeonggon Yoo
2022-04-06  7:29     ` Arnd Bergmann
2022-04-06 12:09       ` Hyeonggon Yoo
2022-04-06  8:53     ` Catalin Marinas
2022-04-08  6:42   ` Hyeonggon Yoo
2022-04-08  9:06     ` Hyeonggon Yoo
2022-04-08  9:11     ` Catalin Marinas
2022-04-11 10:37   ` Hyeonggon Yoo
2022-04-11 14:02     ` Catalin Marinas
2022-04-05 13:57 ` [PATCH 02/10] drivers/base: Use ARCH_DMA_MINALIGN instead of ARCH_KMALLOC_MINALIGN Catalin Marinas
2022-04-11 14:57   ` Andy Shevchenko
2022-04-11 17:39     ` Catalin Marinas
2022-04-05 13:57 ` [PATCH 03/10] drivers/gpu: " Catalin Marinas
2022-04-05 13:57 ` [PATCH 04/10] drivers/md: " Catalin Marinas
2022-04-05 13:57 ` [PATCH 05/10] drivers/spi: " Catalin Marinas
2022-04-05 14:05   ` Mark Brown
2022-04-05 13:57 ` [PATCH 06/10] drivers/usb: " Catalin Marinas
2022-04-05 13:57 ` [PATCH 07/10] crypto: " Catalin Marinas
2022-04-05 22:57   ` Herbert Xu
2022-04-06  6:53     ` Ard Biesheuvel
2022-04-06  8:49       ` Catalin Marinas
2022-04-06  9:41         ` Ard Biesheuvel
2022-04-07  4:30         ` Herbert Xu
2022-04-07 11:01           ` Catalin Marinas
2022-04-07 11:40             ` Herbert Xu
2022-04-07 16:28               ` Catalin Marinas
2022-04-08  3:25                 ` Herbert Xu
2022-04-08  9:04                   ` Catalin Marinas
2022-04-08  9:11                     ` Herbert Xu
2022-04-12  9:32                       ` Catalin Marinas
2022-04-12  9:40                         ` Herbert Xu
2022-04-12 10:02                           ` Catalin Marinas
2022-04-12 10:18                             ` Herbert Xu
2022-04-12 12:31                               ` Catalin Marinas
2022-04-12 22:01                                 ` Ard Biesheuvel
2022-04-13  8:47                                   ` Catalin Marinas
2022-04-13 19:53                                     ` Linus Torvalds
2022-04-14  5:38                                       ` Greg Kroah-Hartman
2022-04-14 13:52                                         ` Ard Biesheuvel
2022-04-14 14:27                                           ` Greg Kroah-Hartman
2022-04-14 14:36                                             ` Ard Biesheuvel
2022-04-14 14:52                                               ` Greg Kroah-Hartman
2022-04-14 15:01                                                 ` Ard Biesheuvel
2022-04-14 15:10                                                   ` Ard Biesheuvel
2022-04-14 19:49                                       ` Catalin Marinas
2022-04-14 22:25                                         ` Linus Torvalds
2022-04-15  6:03                                           ` Ard Biesheuvel
2022-04-15 11:09                                           ` Arnd Bergmann
2022-04-16  9:42                                           ` Catalin Marinas
2022-04-20 19:07                                           ` Catalin Marinas
2022-04-20 19:33                                             ` Linus Torvalds
2022-04-14 14:30                                     ` Ard Biesheuvel
2022-04-15  6:51                                     ` Herbert Xu
2022-04-15  7:49                                       ` Ard Biesheuvel
2022-04-15  7:51                                         ` Herbert Xu
2022-04-15  8:05                                           ` Ard Biesheuvel
2022-04-15  8:12                                             ` Herbert Xu
2022-04-15  9:51                                               ` Ard Biesheuvel
2022-04-15 10:04                                                 ` Ard Biesheuvel
2022-04-15 10:12                                                 ` Herbert Xu
2022-04-15 10:22                                                   ` Ard Biesheuvel
2022-04-15 10:45                                                     ` Herbert Xu
2022-04-15 11:38                                                       ` Ard Biesheuvel
2022-04-17  8:08                                                         ` Herbert Xu
2022-04-17  8:31                                                           ` Catalin Marinas
2022-04-17  8:35                                                             ` Herbert Xu
2022-04-17  8:50                                                               ` Catalin Marinas
2022-04-17  8:58                                                                 ` Herbert Xu
2022-04-17 16:30                                                                   ` Catalin Marinas
2022-04-18  8:37                                                                     ` Herbert Xu
2022-04-18  9:19                                                                       ` Catalin Marinas
2022-04-18 16:44                                                                       ` Catalin Marinas
2022-04-19 21:50                                                                         ` Ard Biesheuvel
2022-04-20 10:36                                                                           ` Catalin Marinas
2022-04-20 11:29                                                                           ` Arnd Bergmann
2022-04-21  7:20                                                                             ` Christoph Hellwig
2022-04-21  7:36                                                                               ` Arnd Bergmann
2022-04-21  7:44                                                                                 ` Christoph Hellwig
2022-04-21  8:05                                                                               ` Ard Biesheuvel
2022-04-21 11:06                                                                               ` Catalin Marinas
2022-04-21 12:28                                                                                 ` Arnd Bergmann
2022-04-21 13:25                                                                                   ` Catalin Marinas
2022-04-21 13:47                                                                                     ` Arnd Bergmann
2022-04-21 14:44                                                                                       ` Catalin Marinas
2022-04-21 14:47                                                                                         ` Arnd Bergmann
2022-05-10 11:03                                                                       ` [RFC PATCH 0/7] crypto: Add helpers for allocating with DMA alignment Herbert Xu
2022-05-10 11:07                                                                         ` [RFC PATCH 1/7] crypto: Prepare to move crypto_tfm_ctx Herbert Xu
2022-05-10 11:07                                                                         ` [RFC PATCH 2/7] crypto: api - Add crypto_tfm_ctx_dma Herbert Xu
2022-05-10 17:10                                                                           ` Catalin Marinas
2022-05-12  3:57                                                                             ` Herbert Xu
2022-05-10 11:07                                                                         ` [RFC PATCH 3/7] crypto: aead - Add ctx helpers with DMA alignment Herbert Xu
2022-05-10 11:07                                                                         ` [RFC PATCH 4/7] crypto: hash " Herbert Xu
2022-05-10 11:07                                                                         ` [RFC PATCH 5/7] crypto: skcipher " Herbert Xu
2022-05-10 11:07                                                                         ` [RFC PATCH 6/7] crypto: api - Increase MAX_ALGAPI_ALIGNMASK to 127 Herbert Xu
2022-05-10 11:07                                                                         ` [RFC PATCH 7/7] crypto: caam - Explicitly request DMA alignment Herbert Xu
2022-04-15 12:18                                             ` [PATCH 07/10] crypto: Use ARCH_DMA_MINALIGN instead of ARCH_KMALLOC_MINALIGN Catalin Marinas
2022-04-15 12:25                                               ` Ard Biesheuvel
2022-04-15  9:51                                           ` Catalin Marinas
2022-04-15 12:31                                             ` Catalin Marinas
2022-04-17  8:11                                               ` Herbert Xu
2022-04-17  8:38                                                 ` Catalin Marinas
2022-04-17  8:43                                                   ` Herbert Xu
2022-04-17 16:29                                                     ` Catalin Marinas
2022-07-15 22:23                                                       ` Isaac Manjarres
2022-07-16  3:25                                                         ` Herbert Xu
2022-07-18 17:53                                                           ` Catalin Marinas
2022-09-21  0:47                                                             ` Isaac Manjarres
2022-09-30 18:32                                                               ` Catalin Marinas
2022-09-30 19:35                                                                 ` Linus Torvalds
2022-10-01 22:29                                                                   ` Catalin Marinas
2022-10-02 17:00                                                                     ` Linus Torvalds
2022-10-02 22:08                                                                       ` Ard Biesheuvel
2022-10-02 22:24                                                                         ` Linus Torvalds
2022-10-03 17:39                                                                           ` Catalin Marinas
2022-10-12 17:45                                                                 ` Isaac Manjarres
2022-10-13 16:57                                                                   ` Catalin Marinas
2022-10-13 18:58                                                                     ` Saravana Kannan
2022-10-14 16:25                                                                       ` Catalin Marinas
2022-10-14 20:23                                                                         ` Saravana Kannan
2022-10-14 20:44                                                                           ` Linus Torvalds
2022-10-16 21:37                                                                             ` Catalin Marinas
2022-04-12 10:20                             ` Catalin Marinas
2022-04-07  6:14   ` Muchun Song
2022-04-07  9:25     ` Catalin Marinas
2022-04-07 10:00       ` Muchun Song
2022-04-07 11:06         ` Catalin Marinas
2022-04-05 13:57 ` [PATCH 08/10] mm/slab: Allow dynamic kmalloc() minimum alignment Catalin Marinas
2022-04-07  3:46   ` Hyeonggon Yoo
2022-04-07  8:50     ` Catalin Marinas
2022-04-07  9:18       ` Hyeonggon Yoo
2022-04-07  9:35         ` Catalin Marinas [this message]
2022-04-07 12:26           ` Hyeonggon Yoo
2022-04-11 11:55   ` Hyeonggon Yoo
2022-04-05 13:57 ` [PATCH 09/10] mm/slab: Simplify create_kmalloc_cache() args and make it static Catalin Marinas
2022-04-05 13:57 ` [PATCH 10/10] arm64: Enable dynamic kmalloc() minimum alignment Catalin Marinas
2022-04-07 14:40 ` [PATCH 00/10] mm, arm64: Reduce ARCH_KMALLOC_MINALIGN below the cache line size Vlastimil Babka
2022-04-07 17:48   ` Catalin Marinas
2022-04-08 14:37     ` Vlastimil Babka

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