Re: [PATCH v3 6/9] mm, memory_hotplug: do not associate hotadded memory to zones until online

From: Vlastimil Babka
Date: Thu Apr 20 2017 - 04:25:40 EST

On 04/10/2017 06:25 PM, Michal Hocko wrote:
> This contains two minor fixes spotted based on testing by Igor Mammedov.
> ---
> From d829579cc7061255f818f9aeaa3aa2cd82fec75a Mon Sep 17 00:00:00 2001
> From: Michal Hocko <mhocko@xxxxxxxx>
> Date: Wed, 29 Mar 2017 16:07:00 +0200
> Subject: [PATCH] mm, memory_hotplug: do not associate hotadded memory to zones
> until online
> MIME-Version: 1.0
> Content-Type: text/plain; charset=UTF-8
> Content-Transfer-Encoding: 8bit
>
> The current memory hotplug implementation relies on having all the
> struct pages associate with a zone/node during the physical hotplug phase
> (arch_add_memory->__add_pages->__add_section->__add_zone). In the vast
> majority of cases this means that they are added to ZONE_NORMAL. This
> has been so since 9d99aaa31f59 ("[PATCH] x86_64: Support memory hotadd
> without sparsemem") and it wasn't a big deal back then because movable
> onlining didn't exist yet.
>
> Much later memory hotplug wanted to (ab)use ZONE_MOVABLE for movable
> onlining 511c2aba8f07 ("mm, memory-hotplug: dynamic configure movable
> memory and portion memory") and then things got more complicated. Rather
> than reconsidering the zone association which was no longer needed
> (because the memory hotplug already depended on SPARSEMEM) a convoluted
> semantic of zone shifting has been developed. Only the currently last
> memblock or the one adjacent to the zone_movable can be onlined movable.
> This essentially means that the online type changes as the new memblocks
> are added.
>
> Let's simulate memory hot online manually
> Normal Movable
>
> /sys/devices/system/memory/memory32/valid_zones:Normal
> /sys/devices/system/memory/memory33/valid_zones:Normal Movable
>
> /sys/devices/system/memory/memory32/valid_zones:Normal
> /sys/devices/system/memory/memory33/valid_zones:Normal
> /sys/devices/system/memory/memory34/valid_zones:Normal Movable
>
> /sys/devices/system/memory/memory32/valid_zones:Normal
> /sys/devices/system/memory/memory33/valid_zones:Normal Movable
> /sys/devices/system/memory/memory34/valid_zones:Movable Normal

Commands seem to be missing above?

> This is an awkward semantic because an udev event is sent as soon as the
> block is onlined and an udev handler might want to online it based on
> some policy (e.g. association with a node) but it will inherently race
> with new blocks showing up.
>
> This patch changes the physical online phase to not associate pages
> with any zone at all. All the pages are just marked reserved and wait
> for the onlining phase to be associated with the zone as per the online
> request. There are only two requirements
> - existing ZONE_NORMAL and ZONE_MOVABLE cannot overlap
> - ZONE_NORMAL precedes ZONE_MOVABLE in physical addresses
> the later on is not an inherent requirement and can be changed in the
> future. It preserves the current behavior and made the code slightly
> simpler. This is subject to change in future.
>
> This means that the same physical online steps as above will lead to the
> following state:
> Normal Movable
>
> /sys/devices/system/memory/memory32/valid_zones:Normal Movable
> /sys/devices/system/memory/memory33/valid_zones:Normal Movable
>
> /sys/devices/system/memory/memory32/valid_zones:Normal Movable
> /sys/devices/system/memory/memory33/valid_zones:Normal Movable
> /sys/devices/system/memory/memory34/valid_zones:Normal Movable
>
> /sys/devices/system/memory/memory32/valid_zones:Normal Movable
> /sys/devices/system/memory/memory33/valid_zones:Normal Movable
> /sys/devices/system/memory/memory34/valid_zones:Movable

Ditto.

> Implementation:
> The current move_pfn_range is reimplemented to check the above
> requirements (allow_online_pfn_range) and then updates the respective
> zone (move_pfn_range_to_zone), the pgdat and links all the pages in the
> pfn range with the zone/node. __add_pages is updated to not require the
> zone and only initializes sections in the range. This allowed to
> simplify the arch_add_memory code (s390 could get rid of quite some
> of code).
>
> devm_memremap_pages is the only user of arch_add_memory which relies
> on the zone association because it only hooks into the memory hotplug
> only half way. It uses it to associate the new memory with ZONE_DEVICE
> but doesn't allow it to be {on,off}lined via sysfs. This means that this
> particular code path has to call move_pfn_range_to_zone explicitly.
>
> The original zone shifting code is kept in place and will be removed in
> the follow up patch for an easier review.
>
> Changes since v1
> - we have to associate the page with the node early (in __add_section),
> because pfn_to_node depends on struct page containing this
> information - based on testing by Reza Arbab
> - resize_{zone,pgdat}_range has to check whether they are popoulated -
> Reza Arbab
> - fix devm_memremap_pages to use pfn rather than physical address -
> Jérôme Glisse
> - move_pfn_range has to check for intersection with zone_movable rather
> than to rely on allow_online_pfn_range(MMOP_ONLINE_MOVABLE) for
> MMOP_ONLINE_KEEP
>
> Changes since v2
> - fix show_valid_zones nr_pages calculation
> - allow_online_pfn_range has to check managed pages rather than present
>
> Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
> Cc: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
> Cc: linux-arch@xxxxxxxxxxxxxxx
> Acked-by: Heiko Carstens <heiko.carstens@xxxxxxxxxx> # For s390 bits
> Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
> ---
> arch/ia64/mm/init.c | 9 +-
> arch/powerpc/mm/mem.c | 10 +-
> arch/s390/mm/init.c | 30 +-----
> arch/sh/mm/init.c | 8 +-
> arch/x86/mm/init_32.c | 5 +-
> arch/x86/mm/init_64.c | 9 +-
> drivers/base/memory.c | 52 ++++++-----
> include/linux/memory_hotplug.h | 13 +--
> include/linux/mmzone.h | 14 +++
> kernel/memremap.c | 4 +
> mm/memory_hotplug.c | 201 +++++++++++++++++++++++++----------------
> mm/sparse.c | 3 +-
> 12 files changed, 186 insertions(+), 172 deletions(-)

...

> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -533,6 +533,20 @@ static inline bool zone_is_empty(struct zone *zone)
> }
>
> /*
> + * Return true if [start_pfn, start_pfn + nr_pages) range has a non-mpty


non-empty

> + * intersection with the given zone
> + */
> +static inline bool zone_intersects(struct zone *zone,
> + unsigned long start_pfn, unsigned long nr_pages)
> +{

I'm looking at your current mmotm tree branch, which looks like this:

+ * Return true if [start_pfn, start_pfn + nr_pages) range has a non-mpty
+ * intersection with the given zone
+ */
+static inline bool zone_intersects(struct zone *zone,
+ unsigned long start_pfn, unsigned long nr_pages)
+{
+ if (zone_is_empty(zone))
+ return false;
+ if (zone->zone_start_pfn <= start_pfn && start_pfn < zone_end_pfn(zone))
+ return true;
+ if (start_pfn + nr_pages > zone->zone_start_pfn)
+ return true;

A false positive is possible here, when start_pfn >= zone_end_pfn(zone)?

+ return false;
+}
+
+/*

...

> @@ -1029,39 +1018,114 @@ static void node_states_set_node(int node, struct memory_notify *arg)
> node_set_state(node, N_MEMORY);
> }
>
> -bool zone_can_shift(unsigned long pfn, unsigned long nr_pages,
> - enum zone_type target, int *zone_shift)
> +bool allow_online_pfn_range(int nid, unsigned long pfn, unsigned long nr_pages, int online_type)
> {
> - struct zone *zone = page_zone(pfn_to_page(pfn));
> - enum zone_type idx = zone_idx(zone);
> - int i;
> + struct pglist_data *pgdat = NODE_DATA(nid);
> + struct zone *movable_zone = &pgdat->node_zones[ZONE_MOVABLE];
> + struct zone *normal_zone = &pgdat->node_zones[ZONE_NORMAL];
>
> - *zone_shift = 0;
> + /*
> + * TODO there shouldn't be any inherent reason to have ZONE_NORMAL
> + * physically before ZONE_MOVABLE. All we need is they do not
> + * overlap. Historically we didn't allow ZONE_NORMAL after ZONE_MOVABLE
> + * though so let's stick with it for simplicity for now.
> + * TODO make sure we do not overlap with ZONE_DEVICE

Is this last TODO a blocker, unlike the others?

...

@ -1074,29 +1138,16 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages, int online_typ
> int nid;
> int ret;
> struct memory_notify arg;
> - int zone_shift = 0;
>
> - /*
> - * This doesn't need a lock to do pfn_to_page().
> - * The section can't be removed here because of the
> - * memory_block->state_mutex.
> - */
> - zone = page_zone(pfn_to_page(pfn));
> -
> - if ((zone_idx(zone) > ZONE_NORMAL ||
> - online_type == MMOP_ONLINE_MOVABLE) &&
> - !can_online_high_movable(pfn_to_nid(pfn)))
> + nid = pfn_to_nid(pfn);
> + if (!allow_online_pfn_range(nid, pfn, nr_pages, online_type))
> return -EINVAL;
>
> - if (online_type == MMOP_ONLINE_KERNEL) {
> - if (!zone_can_shift(pfn, nr_pages, ZONE_NORMAL, &zone_shift))
> - return -EINVAL;
> - } else if (online_type == MMOP_ONLINE_MOVABLE) {
> - if (!zone_can_shift(pfn, nr_pages, ZONE_MOVABLE, &zone_shift))
> - return -EINVAL;
> - }
> + if (online_type == MMOP_ONLINE_MOVABLE && !can_online_high_movable(nid))
> + return -EINVAL;
>
> - zone = move_pfn_range(zone_shift, pfn, pfn + nr_pages);
> + /* associate pfn range with the zone */
> + zone = move_pfn_range(online_type, nid, pfn, nr_pages);
> if (!zone)
> return -EINVAL;

Nit: This !zone currently cannot happen.

>
> @@ -1104,8 +1155,6 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages, int online_typ
> arg.nr_pages = nr_pages;
> node_states_check_changes_online(nr_pages, zone, &arg);
>
> - nid = zone_to_nid(zone);
> -
> ret = memory_notify(MEM_GOING_ONLINE, &arg);
> ret = notifier_to_errno(ret);
> if (ret)
> diff --git a/mm/sparse.c b/mm/sparse.c
> index 6903c8fc3085..d75407882598 100644
> --- a/mm/sparse.c
> +++ b/mm/sparse.c
> @@ -686,10 +686,9 @@ static void free_map_bootmem(struct page *memmap)
> * set. If this is <=0, then that means that the passed-in
> * map was not consumed and must be freed.
> */
> -int __meminit sparse_add_one_section(struct zone *zone, unsigned long start_pfn)
> +int __meminit sparse_add_one_section(struct pglist_data *pgdat, unsigned long start_pfn)
> {
> unsigned long section_nr = pfn_to_section_nr(start_pfn);
> - struct pglist_data *pgdat = zone->zone_pgdat;
> struct mem_section *ms;
> struct page *memmap;
> unsigned long *usemap;
>