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

From: Song, Xiongwei
Date: Tue Nov 28 2023 - 00:19:56 EST



> -----Original Message-----
> From: Vlastimil Babka <vbabka@xxxxxxx>
> Sent: Monday, November 27, 2023 8:03 PM
> To: Song, Xiongwei <Xiongwei.Song@xxxxxxxxxxxxx>; 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
> Subject: Re: [PATCH v2] Documentation: kernel-parameters: remove slab_max_order and
> noaliencache
>
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> On 11/26/23 08:25, Song, Xiongwei wrote:
> > 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.
>
> I'd hope the result look more like this, so the duplicate names are not
> so prominent.
>
> slab_merge [MM]
> Enable merging of slabs with similar size when the
> kernel is built without CONFIG_SLAB_MERGE_DEFAULT.
> (slub_merge also accepted as an alias)
>
> Note that it's not just a Documentation change anymore, as many of the
> parameters don't have the slab_ variants yet wired up.

Ok, thanks. Will create a patch for it.

Regards,
Xiongwei

>
> >
> > 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