RE: [PATCH v2] Documentation: kernel-parameters: remove slab_max_order and noaliencache

["Song, Xiongwei" <Xiongwei.Song@windriver.com>]

Hi Vlastimil,

> -----Original Message-----
> From: Vlastimil Babka <vbabka@suse.cz>
> Sent: Friday, November 24, 2023 7:24 PM
> To: sxwjean@me.com; 42.hyeyoo@gmail.com; linux-mm@kvack.org
> Cc: cl@linux.com; penberg@kernel.org; rientjes@google.com; iamjoonsoo.kim@lge.com;
> akpm@linux-foundation.org; roman.gushchin@linux.dev; corbet@lwn.net; linux-
> doc@vger.kernel.org; linux-kernel@vger.kernel.org; Song, Xiongwei
> <Xiongwei.Song@windriver.com>
> Subject: Re: [PATCH v2] Documentation: kernel-parameters: remove slab_max_order and
> noaliencache
> 
> 
> On 11/22/23 15:36, sxwjean@me.com wrote:
> > From: Xiongwei Song <xiongwei.song@windriver.com>
> >
> > Since slab allocator has already been removed. There is no users about
> > slab_max_order and noaliencache, so let's remove them.
> >
> > Signed-off-by: Xiongwei Song <xiongwei.song@windriver.com>
> > ---
> > v2: Hyeonggon Yoo <42.hyeyoo@gmail.com> suggested that noaliencache should be
> > removed too. Here adding this change. The patch is based on [1].
> >
> > [1] https://git.kernel.org/pub/scm/linux/kernel/git/vbabka/linux.git/log/?h=slab-remove-
> slab-v2r1
> >
> > v1: https://lore.kernel.org/linux-mm/20231120091214.150502-1-
> sxwjean@me.com/T/#m55ebb45851bc86d650baf65dfe8296d33c5b1126
> > ---
> >  Documentation/admin-guide/kernel-parameters.txt | 10 ----------
> >  1 file changed, 10 deletions(-)
> >
> > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-
> guide/kernel-parameters.txt
> > index 65731b060e3f..d56a5beefe24 100644
> > --- a/Documentation/admin-guide/kernel-parameters.txt
> > +++ b/Documentation/admin-guide/kernel-parameters.txt
> > @@ -3740,10 +3740,6 @@
> >       no5lvl          [X86-64,RISCV] Disable 5-level paging mode. Forces
> >                       kernel to use 4-level paging instead.
> >
> > -     noaliencache    [MM, NUMA, SLAB] Disables the allocation of alien
> > -                     caches in the slab allocator.  Saves per-node memory,
> > -                     but will impact performance.
> 
> No question about this one, can be deleted.
> 
> > -
> >       noalign         [KNL,ARM]
> >
> >       noaltinstr      [S390] Disables alternative instructions patching
> > @@ -5887,12 +5883,6 @@
> >                       own.
> >                       For more information see Documentation/mm/slub.rst.
> >
> > -     slab_max_order= [MM, SLAB]
> > -                     Determines the maximum allowed order for slabs.
> > -                     A high setting may cause OOMs due to memory
> > -                     fragmentation.  Defaults to 1 for systems with
> > -                     more than 32MB of RAM, 0 otherwise.
> 
> I think here we should consider the long-term plan first. It's a bit
> unfortunate (in hindsight) SLUB brought its own prefix of parameters, even
> if some became interchangeable aliases later (slab/slub_nomerge), some not.
> I think it would be best to unify them, and consider the string "slub" an
> implementation detail of the general "slab allocator" term going forward.
> 
> So what I'd propose is that we change all parameters to accept a
> "slab_$param" as a primary and documented name (and the description can
> contain just [MM] tag, no [SLAB] or [SLUB] needed), with "slub_$param" is
> also accepted as an alias where it exists today, and there's just a note
> that the slub_$param name is also accepted in the description of the
> canonical parameter, not in a separate description. Then maybe in a few
> years we can mark the old names as deprecated and start issuing low-key
> warnings (while still accepting them), and in 10 years maybe remove them
> completely. Thoughts?

Sorry, I didn't know the SLUB history, thanks for the comments and proposal. 

Did you mean the rough diff below?

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 65731b060e3f..db6d2ebe7c7d 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -5871,10 +5871,12 @@
         slram=          [HW,MTD]

         slab_merge      [MM]
+       slub_merge      [MM]
                         Enable merging of slabs with similar size when the
                         kernel is built without CONFIG_SLAB_MERGE_DEFAULT.

         slab_nomerge    [MM]
+       slub_nomerge    [MM]
                         Disable merging of slabs with similar size. May be
                         necessary if there is some reason to distinguish
                         allocs to different slabs, especially in hardened
@@ -5887,12 +5889,6 @@
                         own.
                         For more information see Documentation/mm/slub.rst.

-       slab_max_order= [MM, SLAB]
-                       Determines the maximum allowed order for slabs.
-                       A high setting may cause OOMs due to memory
-                       fragmentation.  Defaults to 1 for systems with
-                       more than 32MB of RAM, 0 otherwise.
-
         slub_debug[=options[,slabs][;[options[,slabs]]...]      [MM, SLUB]
                         Enabling slub_debug allows one to determine the
                         culprit if slab objects become corrupted. Enabling
@@ -5901,13 +5897,15 @@
                         last alloc / free. For more information see
                         Documentation/mm/slub.rst.

-       slub_max_order= [MM, SLUB]
+       slab_max_order= [MM]
+       slub_max_order= [MM]
                         Determines the maximum allowed order for slabs.
                         A high setting may cause OOMs due to memory
                         fragmentation. For more information see
                         Documentation/mm/slub.rst.

-       slub_min_objects=       [MM, SLUB]
+       slab_min_objects=       [MM]
+       slub_min_objects=       [MM]
                         The minimum number of objects per slab. SLUB will
                         increase the slab order up to slub_max_order to
                         generate a sufficiently large slab able to contain
@@ -5916,18 +5914,12 @@
                         and the less frequently locks need to be acquired.
                         For more information see Documentation/mm/slub.rst.

-       slub_min_order= [MM, SLUB]
+       slub_min_order= [MM]
+       slab_min_order= [MM]
                         Determines the minimum page order for slabs.
Must be
                         lower than slub_max_order.
                         For more information see Documentation/mm/slub.rst.

-       slub_merge      [MM, SLUB]
-                       Same with slab_merge.
-
-       slub_nomerge    [MM, SLUB]
-                       Same with slab_nomerge. This is supported for
legacy.
-                       See slab_nomerge for more information.
-
         smart2=         [HW]
                         Format: <io1>[,<io2>[,...,<io8>]]

If so I think we should use slab_&param in mm/slub.c. When hitting "slub_$param"
we need to assign the value to "slab_&param" like "slab_nomerge", right?

Regards,
Xiongwei