linux-kernel - Re: [RFC PATCH v3 4/4] mm,memory_hotplug: Add mhp_memmap_on

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Date:   Wed, 2 Dec 2020 10:42:18 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Oscar Salvador <osalvador@...e.de>
Cc:     mhocko@...nel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, vbabka@...e.cz, pasha.tatashin@...een.com
Subject: Re: [RFC PATCH v3 4/4] mm,memory_hotplug: Add mhp_memmap_on_memory
 boot option

On 01.12.20 12:51, Oscar Salvador wrote:
> Self stored memmap leads to a sparse memory situation which is unsuitable
> for workloads that requires large contiguous memory chunks.
> 
> Make this an opt-in which needs to be explicitly enabled.
> 
> Signed-off-by: Oscar Salvador <osalvador@...e.de>
> ---
>  mm/memory_hotplug.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 4b4708512f82..858d6161e915 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -42,6 +42,8 @@
>  #include "internal.h"
>  #include "shuffle.h"
>  
> +static bool memmap_on_memory_enabled __read_mostly = false;
> +
>  /*
>   * online_page_callback contains pointer to current page onlining function.
>   * Initially it is generic_online_page(). If it is required it could be
> @@ -1034,7 +1036,7 @@ bool __weak arch_support_memmap_on_memory(void)
>  
>  bool mhp_supports_memmap_on_memory(unsigned long size)
>  {
> -	if (!arch_support_memmap_on_memory() ||
> +	if (!memmap_on_memory_enabled || !arch_support_memmap_on_memory() ||
>  	    !IS_ENABLED(CONFIG_SPARSEMEM_VMEMMAP) ||
>  	    size > memory_block_size_bytes())
>  		return false;
> @@ -1422,6 +1424,13 @@ static int __init cmdline_parse_movable_node(char *p)
>  }
>  early_param("movable_node", cmdline_parse_movable_node);
>  
> +static int __init cmdline_parse_memmap_on_memory(char *p)
> +{
> +	memmap_on_memory_enabled = true;
> +	return 0;
> +}
> +early_param("mhp_memmap_on_memory", cmdline_parse_memmap_on_memory);
> +
>  /* check which state of node_states will be changed when offline memory */
>  static void node_states_check_changes_offline(unsigned long nr_pages,
>  		struct zone *zone, struct memory_notify *arg)
> 

I have another memhp tunable in the works. I suggest doing it like
page_shuffling and using, module parameters instead. Makes this
a bit nicer IMHO.


diff --git a/mm/Makefile b/mm/Makefile
index 069f216e109e..ba7714b5eaa1 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -58,9 +58,13 @@ obj-y                        := filemap.o mempool.o oom_kill.o fadvise.o \
 page-alloc-y := page_alloc.o
 page-alloc-$(CONFIG_SHUFFLE_PAGE_ALLOCATOR) += shuffle.o
 
+# Give "memory_hotplug" its own module-parameter namespace
+memory-hotplug-$(CONFIG_MEMORY_HOTPLUG) := memory_hotplug.o
+
 obj-y += page-alloc.o
 obj-y += init-mm.o
 obj-y += memblock.o
+obj-y += $(memory-hotplug-y)
 
 ifdef CONFIG_MMU
        obj-$(CONFIG_ADVISE_SYSCALLS)   += madvise.o
@@ -82,7 +86,6 @@ obj-$(CONFIG_SLAB) += slab.o
 obj-$(CONFIG_SLUB) += slub.o
 obj-$(CONFIG_KASAN)    += kasan/
 obj-$(CONFIG_FAILSLAB) += failslab.o
-obj-$(CONFIG_MEMORY_HOTPLUG) += memory_hotplug.o
 obj-$(CONFIG_MEMTEST)          += memtest.o
 obj-$(CONFIG_MIGRATION) += migrate.o
 obj-$(CONFIG_TRANSPARENT_HUGEPAGE) += huge_memory.o khugepaged.o


The you can just use module_param/MODULE_PARM_DESC and set the parameter via

"memory_hotplug.memmap_on_memory"

-- 
Thanks,

David / dhildenb