linux-kernel - RE: [PATCH v2 3/3] mm/slub: correct the default value of slub_min

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Message-ID: <PH0PR11MB51922EE600CA6EA6660EBE59EC8AA@PH0PR11MB5192.namprd11.prod.outlook.com>
Date:   Fri, 8 Dec 2023 23:17:12 +0000
From:   "Song, Xiongwei" <Xiongwei.Song@...driver.com>
To:     Vlastimil Babka <vbabka@...e.cz>,
        Hyeonggon Yoo <42.hyeyoo@...il.com>,
        "sxwjean@...com" <sxwjean@...com>
CC:     "cl@...ux.com" <cl@...ux.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "penberg@...nel.org" <penberg@...nel.org>,
        "rientjes@...gle.com" <rientjes@...gle.com>,
        "iamjoonsoo.kim@....com" <iamjoonsoo.kim@....com>,
        "roman.gushchin@...ux.dev" <roman.gushchin@...ux.dev>,
        "corbet@....net" <corbet@....net>,
        "keescook@...omium.org" <keescook@...omium.org>,
        "arnd@...db.de" <arnd@...db.de>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v2 3/3] mm/slub: correct the default value of
 slub_min_objects in doc



> -----Original Message-----
> From: Vlastimil Babka <vbabka@...e.cz>
> Sent: Thursday, December 7, 2023 12:34 AM
> To: Hyeonggon Yoo <42.hyeyoo@...il.com>; sxwjean@...com
> Cc: cl@...ux.com; linux-mm@...ck.org; penberg@...nel.org; rientjes@...gle.com;
> iamjoonsoo.kim@....com; roman.gushchin@...ux.dev; corbet@....net;
> keescook@...omium.org; arnd@...db.de; akpm@...ux-foundation.org;
> gregkh@...uxfoundation.org; linux-doc@...r.kernel.org; linux-kernel@...r.kernel.org; Song,
> Xiongwei <Xiongwei.Song@...driver.com>
> Subject: Re: [PATCH v2 3/3] mm/slub: correct the default value of slub_min_objects in doc
> 
> On 12/5/23 01:53, Hyeonggon Yoo wrote:
> > On Sun, Dec 3, 2023 at 9:16 AM <sxwjean@...com> wrote:
> >>
> >> From: Xiongwei Song <xiongwei.song@...driver.com>
> >>
> >> 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@...driver.com>
> >
> > 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.
> 
> We could say e.g. "(default: automaticaly scaled by number of cpus)"

Ah, looks better.

> 
> > Also, I think patch 2 should update Documentation/mm/slub.rst too.
> > (slub_$param -> slab_param)
> 
> I'd do it as separate patch, not part of patch 2.

Will do. 

Thanks

> 
> >> ---
> >>  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
> >>