linux-kernel - Re: [PATCH] mm/memory_hotplug: Cache auto_movable stats to optimize online check

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Message-ID: <7cf016ec-70e4-4244-82f6-32718dc38cc6@kernel.org>
Date: Sun, 7 Dec 2025 14:30:00 +0100
From: "David Hildenbrand (Red Hat)" <david@...nel.org>
To: Swaraj Gaikwad <swarajgaikwad1925@...il.com>,
 Oscar Salvador <osalvador@...e.de>, Andrew Morton
 <akpm@...ux-foundation.org>,
 "open list:MEMORY HOT(UN)PLUG" <linux-mm@...ck.org>,
 open list <linux-kernel@...r.kernel.org>
Cc: skhan@...uxfoundation.org, david.hunter.linux@...il.com
Subject: Re: [PATCH] mm/memory_hotplug: Cache auto_movable stats to optimize
 online check

On 12/6/25 22:25, Swaraj Gaikwad wrote:
> The auto_movable_can_online_movable() function currently walks all
> populated zones when nid == NUMA_NO_NODE,
> 
> Since adjust_present_page_count() is called every time memory is
> onlined/offlined and already updates present page counts, we can
> maintain cached global statistics that are updated incrementally. This
> eliminates the need to walk all zones for the NUMA_NO_NODE case.
> 
> This patch introduces a static global_auto_movable_stats structure that
> caches kernel_early_pages and movable_pages counts. The cache is updated
> in adjust_present_page_count() whenever pages are onlined/offlined, and
> is read directly in auto_movable_can_online_movable() when
> nid == NUMA_NO_NODE.
> 
> Testing: Built and booted the kernel successfully. Ran the memory
> management test suite in tools/testing/selftests/mm/ with
> ./run_vmtests.sh - all tests passed.
> 
> Signed-off-by: Swaraj Gaikwad <swarajgaikwad1925@...il.com>
> ---
>   mm/memory_hotplug.c | 15 +++++++++++----
>   1 file changed, 11 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 63b9d500ec6c..ba43edba8c92 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -50,6 +50,8 @@ enum {
>   
>   static int memmap_mode __read_mostly = MEMMAP_ON_MEMORY_DISABLE;
>   
> +static struct auto_movable_stats global_auto_movable_stats;
> +
>   static inline unsigned long memory_block_memmap_size(void)
>   {
>   	return PHYS_PFN(memory_block_size_bytes()) * sizeof(struct page);
> @@ -851,9 +853,7 @@ static bool auto_movable_can_online_movable(int nid, struct memory_group *group,
>   
>   	/* Walk all relevant zones and collect MOVABLE vs. KERNEL stats. */
>   	if (nid == NUMA_NO_NODE) {
> -		/* TODO: cache values */

The TODO was a bit unspecific: should have been "cache values if walking 
all zones becomes a performance problem".

Is there a performance impact, or are you able to show a performance 
difference?

-- 
Cheers

David