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

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Date:   Fri, 8 Apr 2022 10:11:47 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Hyeonggon Yoo <42.hyeyoo@...il.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:
> > 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
> 
> 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?

One step at a time. The slob approach is a bit different, doesn't
generate kmalloc-* caches, so I did not look at it yet. Also based on
Vlastimil's email, there is some reworking going on in there already.

> current code seem to break with SLOB on machines that has 128 byte cache lines
> because ARCH_KMALLOC_MINALIGN is 64?

Does it? The point of the #undef above was precisely to make sure
ARCH_KMALLOC_MINALIGN stays the same as ARCH_DMA_MINALIGN when
CONFIG_SLOB is enabled.

-- 
Catalin