linux-kernel - Re: [RFC PATCH v2 1/4] mm,memory_hotplug: Introduce MHP_MEMMAP_ON

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Message-ID: <20201127145955.GT31550@dhcp22.suse.cz>
Date:   Fri, 27 Nov 2020 15:59:55 +0100
From:   Michal Hocko <mhocko@...e.com>
To:     Oscar Salvador <osalvador@...e.de>
Cc:     david@...hat.com, linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        vbabka@...e.cz, pasha.tatashin@...een.com
Subject: Re: [RFC PATCH v2 1/4] mm,memory_hotplug: Introduce
 MHP_MEMMAP_ON_MEMORY

On Wed 25-11-20 12:20:45, Oscar Salvador wrote:
> MHP_MEMMAP_ON_MEMORY tells the system that we want the memmap
> pagetables to be built from the hot-added range.
> 
> Signed-off-by: Oscar Salvador <osalvador@...e.de>

This should be folded into the patch which uses the flag.

> ---
>  include/linux/memory_hotplug.h | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
> index 551093b74596..5b1ea1f8d1ab 100644
> --- a/include/linux/memory_hotplug.h
> +++ b/include/linux/memory_hotplug.h
> @@ -70,6 +70,14 @@ typedef int __bitwise mhp_t;
>   */
>  #define MEMHP_MERGE_RESOURCE	((__force mhp_t)BIT(0))
>  
> +/*
> + * We want memmap (struct page array) to be self contained.
> + * To do so, we will use the beginning of the hot-added range to build
> + * the page tables for the memmap array that describes the entire range.
> + * Only selected architectures support it with SPARSE_VMEMMAP.
> + */
> +#define MHP_MEMMAP_ON_MEMORY	((__force mhp_t)BIT(1))
> +
>  /*
>   * Extended parameters for memory hotplug:
>   * altmap: alternative allocator for memmap array (optional)
> -- 
> 2.26.2

-- 
Michal Hocko
SUSE Labs