linux-kernel - Re: [PATCH v3] SLUB: Add support for per object memory policies

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Message-ID: <7914434f-73f8-7527-9b40-5c4557e2ce1e@gentwo.org>
Date: Wed, 2 Oct 2024 10:52:23 -0700 (PDT)
From: "Christoph Lameter (Ampere)" <cl@...two.org>
To: Vlastimil Babka <vbabka@...e.cz>
cc: Pekka Enberg <penberg@...nel.org>, David Rientjes <rientjes@...gle.com>, 
    Joonsoo Kim <iamjoonsoo.kim@....com>, 
    Andrew Morton <akpm@...ux-foundation.org>, 
    Roman Gushchin <roman.gushchin@...ux.dev>, 
    Hyeonggon Yoo <42.hyeyoo@...il.com>, Yang Shi <shy828301@...il.com>, 
    linux-mm@...ck.org, linux-kernel@...r.kernel.org, 
    linux-arm-kernel@...ts.infradead.org, 
    Huang Shijie <shijie@...amperecomputing.com>
Subject: Re: [PATCH v3] SLUB: Add support for per object memory policies

On Wed, 2 Oct 2024, Vlastimil Babka wrote:

> OK, but we should document this parameter in:
> Documentation/admin-guide/kernel-parameters.rst
> Documentation/mm/slab.rst

mm/slab.rst is empty? I used slub.rst instead.

Here is a patch to add documentation:


>From 510a95b00355fcbf3fb9e0325c1a0f0ef80c6278 Mon Sep 17 00:00:00 2001
From: Christoph Lameter <cl@...two.org>
Date: Wed, 2 Oct 2024 10:27:00 -0700
Subject: [PATCH] Add documentation for the new slab_strict_numa kernel command
 line option

Signed-off-by: Christoph Lameter (Ampere) <cl@...ux.com>
---
 Documentation/admin-guide/kernel-parameters.txt | 10 ++++++++++
 Documentation/mm/slub.rst                       |  9 +++++++++
 2 files changed, 19 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 1518343bbe22..89a4c0ec290c 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -6544,6 +6544,16 @@
 	stifb=		[HW]
 			Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]

+	slab_strict_numa	[MM]
+			Support memory policies on a per object level
+			in the slab allocator. The default is for memory
+			policies to be applied at the folio level when
+			a new folio is needed or a partial folio is
+			retrieved from the lists. Increases overhead
+			in the slab fastpaths but gains more accurate
+			NUMA kernel object placement which helps with slow
+			interconnects in NUMA systems.
+
         strict_sas_size=
 			[X86]
 			Format: <bool>
diff --git a/Documentation/mm/slub.rst b/Documentation/mm/slub.rst
index 60d350d08362..84ca1dc94e5e 100644
--- a/Documentation/mm/slub.rst
+++ b/Documentation/mm/slub.rst
@@ -175,6 +175,15 @@ can be influenced by kernel parameters:
 	``slab_max_order`` to 0, what cause minimum possible order of
 	slabs allocation.

+``slab_strict_numa``
+        Enables the application of memory policies on each
+        allocation. This results in more accurate placement of
+        objects which may result in the reduction of accesses
+        to remote nodes. The default is to only apply memory
+        policies at the folio level when a new folio is acquired
+        or a folio is retrieved from the lists. Enabling this
+        option reduces the fastpath performance of the slab allocator.
+
 SLUB Debug output
 =================

-- 
2.39.5