linux-kernel - Re: [PATCH 4/5] powerpc/memhotplug: Enable MHP_MEMMAP_ON

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Message-ID: <a8fc4fb8-5c88-35a4-4cd7-8cea818acd3a@redhat.com>
Date:   Mon, 11 Jan 2021 17:55:37 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Oscar Salvador <osalvador@...e.de>, akpm@...ux-foundation.org
Cc:     mhocko@...nel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, vbabka@...e.cz, pasha.tatashin@...een.com
Subject: Re: [PATCH 4/5] powerpc/memhotplug: Enable MHP_MEMMAP_ON_MEMORY when
 supported

On 17.12.20 14:07, Oscar Salvador wrote:
> Let the caller check whether it can pass MHP_MEMMAP_ON_MEMORY by
> checking mhp_supports_memmap_on_memory().
> MHP_MEMMAP_ON_MEMORY can only be set in case
> ARCH_MHP_MEMMAP_ON_MEMORY_ENABLE is enabled, the architecture supports
> altmap, and the range to be added spans a single memory block.
> 
> Signed-off-by: Oscar Salvador <osalvador@...e.de>
> ---
>  arch/powerpc/platforms/pseries/hotplug-memory.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/platforms/pseries/hotplug-memory.c b/arch/powerpc/platforms/pseries/hotplug-memory.c
> index 7efe6ec5d14a..a7f68e282ec1 100644
> --- a/arch/powerpc/platforms/pseries/hotplug-memory.c
> +++ b/arch/powerpc/platforms/pseries/hotplug-memory.c
> @@ -610,6 +610,7 @@ static int dlpar_memory_remove_by_ic(u32 lmbs_to_remove, u32 drc_index)
>  
>  static int dlpar_add_lmb(struct drmem_lmb *lmb)
>  {
> +	mhp_t mhp_flags = MHP_NONE;
>  	unsigned long block_sz;
>  	int nid, rc;
>  
> @@ -629,8 +630,10 @@ static int dlpar_add_lmb(struct drmem_lmb *lmb)
>  	if (nid < 0 || !node_possible(nid))
>  		nid = first_online_node;
>  
> +	if (mhp_supports_memmap_on_memory(block_sz))
> +		mhp_flags |= MHP_MEMMAP_ON_MEMORY;
>  	/* Add the memory */
> -	rc = __add_memory(nid, lmb->base_addr, block_sz, MHP_NONE);
> +	rc = __add_memory(nid, lmb->base_addr, block_sz, mhp_flags);
>  	if (rc) {
>  		invalidate_lmb_associativity_index(lmb);
>  		return rc;

With 16MB LMBs it's quite wasteful - you won't even have a huge page
fitting the the remaining part.

I do wonder if we want this on powerpc only with a bigger LMB/memory
block size (e.g., 256 MB, which is AFAIK the maximum usually found).

-- 
Thanks,

David / dhildenb