RE: [PATCH v2 3/3] mm/slub: correct the default value of slub_min_objects in doc

[Song, Xiongwei]

Hi Hyeonggon,

> -----Original Message-----
> From: Hyeonggon Yoo <42.hyeyoo@xxxxxxxxx>
> Sent: Tuesday, December 5, 2023 8:54 AM
> To: sxwjean@xxxxxx
> Cc: vbabka@xxxxxxx; cl@xxxxxxxxx; linux-mm@xxxxxxxxx; penberg@xxxxxxxxxx;
> rientjes@xxxxxxxxxx; iamjoonsoo.kim@xxxxxxx; roman.gushchin@xxxxxxxxx;
> corbet@xxxxxxx; keescook@xxxxxxxxxxxx; arnd@xxxxxxxx; akpm@xxxxxxxxxxxxxxxxxxxx;
> gregkh@xxxxxxxxxxxxxxxxxxx; linux-doc@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; Song,
> Xiongwei <Xiongwei.Song@xxxxxxxxxxxxx>
> Subject: Re: [PATCH v2 3/3] mm/slub: correct the default value of slub_min_objects in doc
> 
> On Sun, Dec 3, 2023 at 9:16 AM <sxwjean@xxxxxx> wrote:
> >
> > From: Xiongwei Song <xiongwei.song@xxxxxxxxxxxxx>
> >
> > There is no a value assigned to slub_min_objects by default, it always
> > is 0 that is initialized by compiler if no assigned value by command line.
> > min_objects is calculated based on processor numbers in calculate_order().
> > For more details, see commit 9b2cd506e5f2 ("slub: Calculate min_objects
> > based on number of processors.")
> >
> > Signed-off-by: Xiongwei Song <xiongwei.song@xxxxxxxxxxxxx>
> 
> While slub_min_objects equals zero by default, 'min_objects' overrides it to
> 4 * (fls(nr_cpus) + 1) when not set. so when slub_min_objects is not
> set, it would be
> equal to or higher than 4. I'm not sure this level of implementation
> detail is worth documenting.

commit 9b2cd506e5f2 ("slub: Calculate min_objects based on number of processors.")
has already given "processors min_objects" pair, do we really need to document
the specific detail?

> 
> Also, I think patch 2 should update Documentation/mm/slub.rst too.
> (slub_$param -> slab_param)
I think people can know slub_$params are still supported by
Documentation/mm/slub.rst, so we don't need to say the info again in
this file.  Is it better to do so just before removing slub_$params
completely?

Regards,
Xiongwei

> 
> > ---
> >  Documentation/mm/slub.rst | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/Documentation/mm/slub.rst b/Documentation/mm/slub.rst
> > index be75971532f5..1f4399581449 100644
> > --- a/Documentation/mm/slub.rst
> > +++ b/Documentation/mm/slub.rst
> > @@ -150,7 +150,7 @@ list_lock once in a while to deal with partial slabs. That overhead is
> >  governed by the order of the allocation for each slab. The allocations
> >  can be influenced by kernel parameters:
> >
> > -.. slub_min_objects=x          (default 4)
> > +.. slub_min_objects=x          (default 0)
> >  .. slub_min_order=x            (default 0)
> >  .. slub_max_order=x            (default 3 (PAGE_ALLOC_COSTLY_ORDER))
> >
> > --
> > 2.34.1
> >