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Message-ID: <2f8e8e28-28d4-b0a4-11a8-639f78c319c3@suse.cz>
Date: Mon, 27 Nov 2023 13:02:31 +0100
From: Vlastimil Babka <vbabka@...e.cz>
To: "Song, Xiongwei" <Xiongwei.Song@...driver.com>,
"sxwjean@...com" <sxwjean@...com>,
"42.hyeyoo@...il.com" <42.hyeyoo@...il.com>,
"linux-mm@...ck.org" <linux-mm@...ck.org>
Cc: "cl@...ux.com" <cl@...ux.com>,
"penberg@...nel.org" <penberg@...nel.org>,
"rientjes@...gle.com" <rientjes@...gle.com>,
"iamjoonsoo.kim@....com" <iamjoonsoo.kim@....com>,
"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
"roman.gushchin@...ux.dev" <roman.gushchin@...ux.dev>,
"corbet@....net" <corbet@....net>,
"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] Documentation: kernel-parameters: remove
slab_max_order and noaliencache
On 11/26/23 08:25, Song, Xiongwei wrote:
> Hi Vlastimil,
>
>> -----Original Message-----
>> From: Vlastimil Babka <vbabka@...e.cz>
>> Sent: Friday, November 24, 2023 7:24 PM
>> To: sxwjean@...com; 42.hyeyoo@...il.com; linux-mm@...ck.org
>> Cc: cl@...ux.com; penberg@...nel.org; rientjes@...gle.com; iamjoonsoo.kim@....com;
>> akpm@...ux-foundation.org; roman.gushchin@...ux.dev; corbet@....net; linux-
>> doc@...r.kernel.org; linux-kernel@...r.kernel.org; Song, Xiongwei
>> <Xiongwei.Song@...driver.com>
>> Subject: Re: [PATCH v2] Documentation: kernel-parameters: remove slab_max_order and
>> noaliencache
>>
>>
>> On 11/22/23 15:36, sxwjean@...com wrote:
>> > From: Xiongwei Song <xiongwei.song@...driver.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@...driver.com>
>> > ---
>> > v2: Hyeonggon Yoo <42.hyeyoo@...il.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@...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.
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.
>
> 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_¶m in mm/slub.c. When hitting "slub_$param"
> we need to assign the value to "slab_¶m" like "slab_nomerge", right?
>
> Regards,
> Xiongwei
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