linux-kernel - Re: [PATCH v3 07/35] mm/slab: introduce SLAB_NO_OBJ_EXT to avoid obj

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Date: Thu, 15 Feb 2024 16:37:09 -0500
From: Kent Overstreet <kent.overstreet@...ux.dev>
To: Vlastimil Babka <vbabka@...e.cz>
Cc: Suren Baghdasaryan <surenb@...gle.com>, akpm@...ux-foundation.org, 
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Subject: Re: [PATCH v3 07/35] mm/slab: introduce SLAB_NO_OBJ_EXT to avoid
 obj_ext creation

On Thu, Feb 15, 2024 at 10:31:06PM +0100, Vlastimil Babka wrote:
> On 2/12/24 22:38, Suren Baghdasaryan wrote:
> > Slab extension objects can't be allocated before slab infrastructure is
> > initialized. Some caches, like kmem_cache and kmem_cache_node, are created
> > before slab infrastructure is initialized. Objects from these caches can't
> > have extension objects. Introduce SLAB_NO_OBJ_EXT slab flag to mark these
> > caches and avoid creating extensions for objects allocated from these
> > slabs.
> > 
> > Signed-off-by: Suren Baghdasaryan <surenb@...gle.com>
> > ---
> >  include/linux/slab.h | 7 +++++++
> >  mm/slub.c            | 5 +++--
> >  2 files changed, 10 insertions(+), 2 deletions(-)
> > 
> > diff --git a/include/linux/slab.h b/include/linux/slab.h
> > index b5f5ee8308d0..3ac2fc830f0f 100644
> > --- a/include/linux/slab.h
> > +++ b/include/linux/slab.h
> > @@ -164,6 +164,13 @@
> >  #endif
> >  #define SLAB_TEMPORARY		SLAB_RECLAIM_ACCOUNT	/* Objects are short-lived */
> >  
> > +#ifdef CONFIG_SLAB_OBJ_EXT
> > +/* Slab created using create_boot_cache */
> > +#define SLAB_NO_OBJ_EXT         ((slab_flags_t __force)0x20000000U)
> 
> There's
>    #define SLAB_SKIP_KFENCE        ((slab_flags_t __force)0x20000000U)
> already, so need some other one?

What's up with the order of flags in that file? They don't seem to
follow any particular ordering.

Seems like some cleanup is in order, but any history/context we should
know first?