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 14:10:09 -0800
From: Suren Baghdasaryan <surenb@...gle.com>
To: Vlastimil Babka <vbabka@...e.cz>
Cc: Kent Overstreet <kent.overstreet@...ux.dev>, akpm@...ux-foundation.org, mhocko@...e.com, 
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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 1:50 PM Vlastimil Babka <vbabka@...e.cz> wrote:
>
> On 2/15/24 22:37, Kent Overstreet wrote:
> > 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?

Indeed. I somehow missed it. Thanks for noticing, will fix this in the
next version.

> >
> > What's up with the order of flags in that file? They don't seem to
> > follow any particular ordering.
>
> Seems mostly in increasing order, except commit 4fd0b46e89879 broke it for
> SLAB_RECLAIM_ACCOUNT?
>
> > Seems like some cleanup is in order, but any history/context we should
> > know first?
>
> Yeah noted, but no need to sidetrack you.