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

From: Song, Xiongwei
Date: Sun Nov 26 2023 - 02:25:59 EST

Hi Vlastimil,

> -----Original Message-----
> From: Vlastimil Babka <vbabka@xxxxxxx>
> Sent: Friday, November 24, 2023 7:24 PM
> To: sxwjean@xxxxxx; 42.hyeyoo@xxxxxxxxx; linux-mm@xxxxxxxxx
> Cc: cl@xxxxxxxxx; penberg@xxxxxxxxxx; rientjes@xxxxxxxxxx; iamjoonsoo.kim@xxxxxxx;
> akpm@xxxxxxxxxxxxxxxxxxxx; roman.gushchin@xxxxxxxxx; corbet@xxxxxxx; linux-
> doc@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; Song, Xiongwei
> <Xiongwei.Song@xxxxxxxxxxxxx>
> Subject: Re: [PATCH v2] Documentation: kernel-parameters: remove slab_max_order and
> noaliencache
>
>
> On 11/22/23 15:36, sxwjean@xxxxxx wrote:
> > From: Xiongwei Song <xiongwei.song@xxxxxxxxxxxxx>
> >
> > 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@xxxxxxxxxxxxx>
> > ---
> > v2: Hyeonggon Yoo <42.hyeyoo@xxxxxxxxx> 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@xxxxxx/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