linux-kernel - Re: [PATCH v2] mm: make minimum slab alignment a runtime property

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Message-ID: <CAMn1gO77+Smgezkx0o5t+MnLJK9KUNpEb+xiJ3Pkoj4pFD1JfQ@mail.gmail.com>
Date:   Fri, 22 Apr 2022 13:08:20 -0700
From:   Peter Collingbourne <pcc@...gle.com>
To:     Catalin Marinas <catalin.marinas@....com>
Cc:     Andrey Konovalov <andreyknvl@...il.com>,
        Hyeonggon Yoo <42.hyeyoo@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Pekka Enberg <penberg@...nel.org>, roman.gushchin@...ux.dev,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        David Rientjes <rientjes@...gle.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Andrey Ryabinin <ryabinin.a.a@...il.com>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        kasan-dev <kasan-dev@...glegroups.com>,
        Eric Biederman <ebiederm@...ssion.com>,
        Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH v2] mm: make minimum slab alignment a runtime property

On Fri, Apr 22, 2022 at 11:03 AM Catalin Marinas
<catalin.marinas@....com> wrote:
>
> On Thu, Apr 21, 2022 at 02:15:48PM -0700, Peter Collingbourne wrote:
> > diff --git a/include/linux/slab.h b/include/linux/slab.h
> > index 373b3ef99f4e..80e517593372 100644
> > --- a/include/linux/slab.h
> > +++ b/include/linux/slab.h
> > @@ -201,21 +201,33 @@ void kmem_dump_obj(void *object);
> >  #endif
> >
> >  /*
> > - * Setting ARCH_SLAB_MINALIGN in arch headers allows a different alignment.
> > + * Setting ARCH_SLAB_MIN_MINALIGN in arch headers allows a different alignment.
> >   * Intended for arches that get misalignment faults even for 64 bit integer
> >   * aligned buffers.
> >   */
> > -#ifndef ARCH_SLAB_MINALIGN
> > -#define ARCH_SLAB_MINALIGN __alignof__(unsigned long long)
> > +#ifndef ARCH_SLAB_MIN_MINALIGN
> > +#define ARCH_SLAB_MIN_MINALIGN __alignof__(unsigned long long)
> > +#endif
>
> Sorry, only a drive-by comment, I'll look at the arm64 parts next week.
> I've seen it mentioned in the first version, what's the point of MIN_MIN
> and not just MIN?

I tried to explain it here:
https://lore.kernel.org/all/CAMn1gO5xHZvFSSsW5sTVaUBN_gS-cYYNMG3PnpgCmh7kk_Zx7Q@mail.gmail.com/

In the end I decided to go back to MIN so this is moot.

Peter