linux-kernel - Re: [PATCH v4 4/5] s390/mm: implement MEM_PREPARE_ONLINE/MEM_FINISH

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Date:   Tue, 28 Nov 2023 12:12:00 +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 v4 4/5] s390/mm: implement
 MEM_PREPARE_ONLINE/MEM_FINISH_OFFLINE notifiers

On 28.11.23 12:03, Sumanth Korikkar wrote:
> MEM_PREPARE_ONLINE memory notifier makes memory block physical
> accessible via sclp assign command. The notifier ensures self-contained
> memory maps are accessible and hence enabling the "memmap on memory" on
> s390.
> 
> MEM_FINISH_OFFLINE memory notifier shifts the memory block to an
> inaccessible state via sclp unassign command.
> 
> 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.
> * 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_PREPARE_ONLINE already executes the sclp assign
>    command.
> * The MEM_CANCEL_ONLINE/MEM_OFFLINE notifier now performs no operation, as
>    MEM_FINISH_OFFLINE already executes the sclp unassign command.
> 
> Reviewed-by: Gerald Schaefer <gerald.schaefer@...ux.ibm.com>
> Signed-off-by: Sumanth Korikkar <sumanthk@...ux.ibm.com>
> ---
>   drivers/s390/char/sclp_cmd.c | 47 +++++++++++++++++++++++++++++++-----
>   1 file changed, 41 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/s390/char/sclp_cmd.c b/drivers/s390/char/sclp_cmd.c
> index 355e63e44e95..c551dc6734fe 100644
> --- a/drivers/s390/char/sclp_cmd.c
> +++ b/drivers/s390/char/sclp_cmd.c
> @@ -18,6 +18,7 @@
>   #include <linux/mm.h>
>   #include <linux/mmzone.h>
>   #include <linux/memory.h>
> +#include <linux/memory_hotplug.h>
>   #include <linux/module.h>
>   #include <asm/ctlreg.h>
>   #include <asm/chpid.h>
> @@ -26,6 +27,7 @@
>   #include <asm/sclp.h>
>   #include <asm/numa.h>
>   #include <asm/facility.h>
> +#include <asm/page-states.h>
>   
>   #include "sclp.h"
>   
> @@ -319,6 +321,7 @@ static bool contains_standby_increment(unsigned long start, unsigned long end)
>   static int sclp_mem_notifier(struct notifier_block *nb,
>   			     unsigned long action, void *data)
>   {
> +	unsigned long altmap_start, altmap_size;
>   	unsigned long start, size;
>   	struct memory_notify *arg;
>   	unsigned char id;
> @@ -340,13 +343,43 @@ static int sclp_mem_notifier(struct notifier_block *nb,
>   		if (contains_standby_increment(start, start + size))
>   			rc = -EPERM;
>   		break;
> -	case MEM_GOING_ONLINE:
> +	case MEM_PREPARE_ONLINE:
> +		/*
> +		 * Access the altmap_start_pfn and altmap_nr_pages fields
> +		 * within the struct memory_notify specifically when dealing
> +		 * with only MEM_PREPARE_ONLINE/MEM_PREPARE_OFFLINE notifiers.
> +		 */
> +		altmap_start = arg->altmap_start_pfn << PAGE_SHIFT;
> +		altmap_size = arg->altmap_nr_pages << PAGE_SHIFT;

PFN_PHYS(), maybe you can directly do:

if (arg->altmap_start_pfn) {
	start = PFN_PHYS(arg->altmap_start_pfn);
	size += PFN_PHYS(arg->altmap_nr_pages);
}

...

and avoid the variables completely.

Reviewed-by: David Hildenbrand <david@...hat.com>

>   	default:
> @@ -397,7 +430,9 @@ static void __init add_memory_merged(u16 rn)
>   	if (!size)
>   		goto skip_add;
>   	for (addr = start; addr < start + size; addr += block_size)
> -		add_memory(0, addr, block_size, MHP_NONE);
> +		add_memory(0, addr, block_size,
> +			   MACHINE_HAS_EDAT1 ?
> +			   MHP_MEMMAP_ON_MEMORY | MHP_OFFLINE_INACCESSIBLE : MHP_NONE);
>   skip_add:
>   	first_rn = rn;
>   	num = 1;

That hunk is likely better moved to the last enabling patch.

-- 
Cheers,

David / dhildenb