linux-kernel - Re: [PATCH 6/8] s390/mm: implement MEM_PHYS_ONLINE MEM_PHYS

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Date:   Tue, 14 Nov 2023 19:39:40 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Sumanth Korikkar <sumanthk@...ux.ibm.com>,
        linux-mm <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Oscar Salvador <osalvador@...e.de>, Michal Hocko <mhocko@...e.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Gerald Schaefer <gerald.schaefer@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        linux-s390 <linux-s390@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 6/8] s390/mm: implement MEM_PHYS_ONLINE MEM_PHYS_OFFLINE
 memory notifiers

On 14.11.23 19:02, Sumanth Korikkar wrote:
> Implement MEM_PHYS_ONLINE and MEM_PHYS_OFFLINE memory notifiers on s390
> 
> Implementation of MEM_PHYS_ONLINE Memory Notifier:
> * Transition the memory block to an accessible/online state using the
>    sclp assign command.
> * Execute __add_pages() for the memory block, enabling a self-contained
>    memory map range. For boot-time memory, vmemmap mapping is carried out
>    through sparse_init().
> 
> Implementation of MEM_PHYS_OFFLINE Memory Notifier:
> * Execute __remove_pages() exclusively for the memory block (applicable
>    where a self-contained memory map was possible before).
> * Shift the memory block to an inaccessible/offline state using the sclp
>    unassign command.
> 
> Additional Implementation Considerations:
> * When MHP_MEMMAP_ON_MEMORY is disabled, the system retains the old
>    behavior. This means the memory map is allocated from default memory,
>    and struct vmemmap pages are populated during the standby memory
>    detection phase.
> * With MHP_MEMMAP_ON_MEMORY enabled (allowing self-contained memory
>    map), the memory map is allocated using the self-contained memory map
>    range. Struct vmemmap pages are populated during the memory hotplug
>    phase.
> * If MACHINE_HAS_EDAT1 is unavailable, MHP_MEMMAP_ON_MEMORY is
>    automatically disabled. This ensures that vmemmap pagetables do not
>    consume additional memory from the default memory allocator.
> * The MEM_GOING_ONLINE notifier has been modified to perform no
>    operation, as MEM_PHYS_ONLINE already executes the sclp assign
>    command.
> * The MEM_CANCEL_ONLINE notifier now performs no operation, as
>    MEM_PHYS_OFFLINE already executes the sclp unassign command.
> * The call to __add_pages() in arch_add_memory() with altmap support is
>    skipped. This operation is deferred and will be performed later in the
>    MEM_PHYS_ONLINE notifier.
> 
> Reviewed-by: Gerald Schaefer <gerald.schaefer@...ux.ibm.com>
> Signed-off-by: Sumanth Korikkar <sumanthk@...ux.ibm.com>
> ---
>   arch/s390/mm/init.c          | 16 +++++++++++++++-
>   drivers/s390/char/sclp_cmd.c | 33 ++++++++++++++++++++++++++++++---
>   2 files changed, 45 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/s390/mm/init.c b/arch/s390/mm/init.c
> index 8d9a60ccb777..db505ed590b2 100644
> --- a/arch/s390/mm/init.c
> +++ b/arch/s390/mm/init.c
> @@ -288,6 +288,12 @@ int arch_add_memory(int nid, u64 start, u64 size,
>   	rc = vmem_add_mapping(start, size);
>   	if (rc)
>   		return rc;
> +	/*
> +	 * If MHP_MEMMAP_ON_MEMORY is enabled, perform __add_pages() during memory
> +	 * onlining phase
> +	 */
> +	if (params->altmap)
> +		return 0;


So we'd have added memory blocks without a memmap? Sorry, but this seems 
to further hack into the s390x direction.

Maybe s390x should just provide a dedicate interface to add these memory 
blocks instead of adding them during boot and then relying on the old 
way of using online/offline set them online/offline.

-- 
Cheers,

David / dhildenb