linux-kernel - Re: [PATCH 01/10] mm/slab: Decouple ARCH_KMALLOC_MINALIGN from ARCH_DMA

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Message-ID: <Yk/7MrhcdR5PaKHd@hyeyoo>
Date:   Fri, 8 Apr 2022 18:06:58 +0900
From:   Hyeonggon Yoo <42.hyeyoo@...il.com>
To:     Catalin Marinas <catalin.marinas@....com>
Cc:     Will Deacon <will@...nel.org>, Marc Zyngier <maz@...nel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-mm@...ck.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 01/10] mm/slab: Decouple ARCH_KMALLOC_MINALIGN from
 ARCH_DMA_MINALIGN

On Fri, Apr 08, 2022 at 03:42:13PM +0900, Hyeonggon Yoo wrote:
> On Tue, Apr 05, 2022 at 02:57:49PM +0100, Catalin Marinas wrote:
> > In preparation for supporting a dynamic kmalloc() minimum alignment,
> > allow architectures to define ARCH_KMALLOC_MINALIGN independently of
> > ARCH_DMA_MINALIGN. In addition, always define ARCH_DMA_MINALIGN even if
> > an architecture does not override it.
> > 
> > After this patch, ARCH_DMA_MINALIGN is expected to be used in static
> > alignment annotations and defined by an architecture to be the maximum
> > alignment for all supported configurations/SoCs in a single Image.
> > ARCH_KMALLOC_MINALIGN, if different, is the minimum alignment guaranteed
> > by kmalloc().
> > 
> > Signed-off-by: Catalin Marinas <catalin.marinas@....com>
> > Cc: Andrew Morton <akpm@...ux-foundation.org>
> > ---
> >  include/linux/slab.h | 23 ++++++++++++++++++-----
> >  1 file changed, 18 insertions(+), 5 deletions(-)
> > 
> > diff --git a/include/linux/slab.h b/include/linux/slab.h
> > index 373b3ef99f4e..d58211bdeceb 100644
> > --- a/include/linux/slab.h
> > +++ b/include/linux/slab.h
> > @@ -187,17 +187,30 @@ bool kmem_valid_obj(void *object);
> >  void kmem_dump_obj(void *object);
> >  #endif
> >  
> > +/*
> > + * slob does not support independent control of ARCH_KMALLOC_MINALIGN and
> > + * ARCH_DMA_MINALIGN.
> > + */
> > +#ifdef CONFIG_SLOB
> > +#undef ARCH_KMALLOC_MINALIGN
> > +#endif
> 

Sorry for the noise. Yeah, the code above is making
ARCH_KMALLOC_MINALIGN = ARCH_DMA_MINALIGN.

I was confused :(

> I think you should replace ARCH_KMALLOC_MINALIGN with ARCH_DMA_MINALIGN
> in mm/slob.c too? Or detect minimum kmalloc alignment in runtime like SLAB/SLUB?
> 
> current code seem to break with SLOB on machines that has 128 byte cache lines
> because ARCH_KMALLOC_MINALIGN is 64?
> 

> > +
> >  /*
> >   * Some archs want to perform DMA into kmalloc caches and need a guaranteed
> >   * alignment larger than the alignment of a 64-bit integer.
> > - * Setting ARCH_KMALLOC_MINALIGN in arch headers allows that.
> > + * Setting ARCH_DMA_MINALIGN in arch headers allows that.
> >   */
> > -#if defined(ARCH_DMA_MINALIGN) && ARCH_DMA_MINALIGN > 8
> > +#ifndef ARCH_DMA_MINALIGN
> > +#define ARCH_DMA_MINALIGN __alignof__(unsigned long long)
> > +#elif ARCH_DMA_MINALIGN > 8 && !defined(ARCH_KMALLOC_MINALIGN)
> >  #define ARCH_KMALLOC_MINALIGN ARCH_DMA_MINALIGN
> > -#define KMALLOC_MIN_SIZE ARCH_DMA_MINALIGN
> > -#define KMALLOC_SHIFT_LOW ilog2(ARCH_DMA_MINALIGN)
> > -#else
> > +#endif
> > +
> > +#ifndef ARCH_KMALLOC_MINALIGN
> >  #define ARCH_KMALLOC_MINALIGN __alignof__(unsigned long long)
> > +#else
> > +#define KMALLOC_MIN_SIZE ARCH_KMALLOC_MINALIGN
> > +#define KMALLOC_SHIFT_LOW ilog2(KMALLOC_MIN_SIZE)
> >  #endif
> >  
> >  /*
> > 
> 
> -- 
> Thanks,
> Hyeonggon

-- 
Thanks,
Hyeonggon