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SubjectRe: [PATCH v4 4/5] s390/mm: implement MEM_PREPARE_ONLINE/MEM_FINISH_OFFLINE notifiers
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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@linux.ibm.com>
> Signed-off-by: Sumanth Korikkar <sumanthk@linux.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@redhat.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

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