Re: [PATCH 06/12] mm, slub: don't create kmalloc-rcl caches with CONFIG_SLUB_TINY

[Vlastimil Babka <vbabka@suse.cz>]

On 11/21/22 18:11, Vlastimil Babka wrote:
> Distinguishing kmalloc(__GFP_RECLAIMABLE) can help against fragmentation
> by grouping pages by mobility, but on tiny systems the extra memory
> overhead of separate set of kmalloc-rcl caches will probably be worse,
> and mobility grouping likely disabled anyway.
> 
> Thus with CONFIG_SLUB_TINY, don't create kmalloc-rcl caches and use the
> regular ones.
> 
> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>

Fixed up in response to lkp report for a MEMCG_KMEM+SLUB_TINY combo:
---8<---
From c1ec0b924850a2863d061f316615d596176f15bb Mon Sep 17 00:00:00 2001
From: Vlastimil Babka <vbabka@suse.cz>
Date: Tue, 15 Nov 2022 18:19:28 +0100
Subject: [PATCH 06/12] mm, slub: don't create kmalloc-rcl caches with
 CONFIG_SLUB_TINY

Distinguishing kmalloc(__GFP_RECLAIMABLE) can help against fragmentation
by grouping pages by mobility, but on tiny systems the extra memory
overhead of separate set of kmalloc-rcl caches will probably be worse,
and mobility grouping likely disabled anyway.

Thus with CONFIG_SLUB_TINY, don't create kmalloc-rcl caches and use the
regular ones.

Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
---
 include/linux/slab.h |  9 +++++++--
 mm/slab_common.c     | 10 ++++++++--
 2 files changed, 15 insertions(+), 4 deletions(-)

diff --git a/include/linux/slab.h b/include/linux/slab.h
index 45efc6c553b8..ae2d19ec8467 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -336,12 +336,17 @@ enum kmalloc_cache_type {
 #endif
 #ifndef CONFIG_MEMCG_KMEM
 	KMALLOC_CGROUP = KMALLOC_NORMAL,
-#else
-	KMALLOC_CGROUP,
 #endif
+#ifdef CONFIG_SLUB_TINY
+	KMALLOC_RECLAIM = KMALLOC_NORMAL,
+#else
 	KMALLOC_RECLAIM,
+#endif
 #ifdef CONFIG_ZONE_DMA
 	KMALLOC_DMA,
+#endif
+#ifdef CONFIG_MEMCG_KMEM
+	KMALLOC_CGROUP,
 #endif
 	NR_KMALLOC_TYPES
 };
diff --git a/mm/slab_common.c b/mm/slab_common.c
index a8cb5de255fc..907d52963806 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -770,10 +770,16 @@ EXPORT_SYMBOL(kmalloc_size_roundup);
 #define KMALLOC_CGROUP_NAME(sz)
 #endif
 
+#ifndef CONFIG_SLUB_TINY
+#define KMALLOC_RCL_NAME(sz)	.name[KMALLOC_RECLAIM] = "kmalloc-rcl-" #sz,
+#else
+#define KMALLOC_RCL_NAME(sz)
+#endif
+
 #define INIT_KMALLOC_INFO(__size, __short_size)			\
 {								\
 	.name[KMALLOC_NORMAL]  = "kmalloc-" #__short_size,	\
-	.name[KMALLOC_RECLAIM] = "kmalloc-rcl-" #__short_size,	\
+	KMALLOC_RCL_NAME(__short_size)				\
 	KMALLOC_CGROUP_NAME(__short_size)			\
 	KMALLOC_DMA_NAME(__short_size)				\
 	.size = __size,						\
@@ -859,7 +865,7 @@ void __init setup_kmalloc_cache_index_table(void)
 static void __init
 new_kmalloc_cache(int idx, enum kmalloc_cache_type type, slab_flags_t flags)
 {
-	if (type == KMALLOC_RECLAIM) {
+	if ((KMALLOC_RECLAIM != KMALLOC_NORMAL) && (type == KMALLOC_RECLAIM)) {
 		flags |= SLAB_RECLAIM_ACCOUNT;
 	} else if (IS_ENABLED(CONFIG_MEMCG_KMEM) && (type == KMALLOC_CGROUP)) {
 		if (mem_cgroup_kmem_disabled()) {
-- 
2.38.1