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 22:50:36 +0100
From: Vlastimil Babka <vbabka@...e.cz>
To: Kent Overstreet <kent.overstreet@...ux.dev>
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 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?
> 
> 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.