(2014/10/31 18:46), Tang Chen wrote:
> When we are doing memory hot-add, the following functions are called:
>
> add_memory()
> |--> hotadd_new_pgdat()
> |--> free_area_init_node()
> |--> free_area_init_core()
> |--> zone->present_pages = realsize; /* 1. zone is populated */
> |--> zone_pcp_init()
> |--> zone->pageset = &boot_pageset; /* 2. zone->pageset is set to boot_pageset */
>
> There are two problems here:
> 1. Zones could be populated before any memory is onlined.
> 2. All the zones on a newly added node have the same pageset pointing to boot_pageset.
>
> The above two problems will result in the following problem:
> When we online memory on one node, e.g node2, the following code is executed:
>
> online_pages()
> {
> ......
> if (!populated_zone(zone)) {
> need_zonelists_rebuild = 1;
> build_all_zonelists(NULL, zone);
> }
> ......
> }
>
> Because of problem 1, the zone has been populated, and the build_all_zonelists()
> will never called. zone->pageset won't be updated.
> Because of problem 2, All the zones on a newly added node have the same pageset
> pointing to boot_pageset.
> And as a result, when we online memory on node2, node3's meminfo will corrupt.
> Pages on node2 may be freed to node3.
>
> # for ((i = 2048; i < 2064; i++)); do echo online_movable > /sys/devices/system/node/node2/memory$i/state; done
> # cat /sys/devices/system/node/node2/meminfo
> Node 2 MemTotal: 33554432 kB
> Node 2 MemFree: 33549092 kB
> Node 2 MemUsed: 5340 kB
> ......
> # cat /sys/devices/system/node/node3/meminfo
> Node 3 MemTotal: 0 kB
> Node 3 MemFree: 248 kB /* corrupted */
> Node 3 MemUsed: 0 kB
> ......
>
> We have to populate some zones before onlining memory, otherwise no memory could be onlined.
> So when onlining pages, we should also check if zone->pageset is pointing to boot_pageset.
>
> Signed-off-by: Gu Zheng <guz.fnst@xxxxxxxxxxxxxx>
> Signed-off-by: Tang Chen <tangchen@xxxxxxxxxxxxxx>
> ---
> include/linux/mm.h | 1 +
> mm/memory_hotplug.c | 6 +++++-
> mm/page_alloc.c | 5 +++++
> 3 files changed, 11 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 02d11ee..83e6505 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -1732,6 +1732,7 @@ void warn_alloc_failed(gfp_t gfp_mask, int order, const char *fmt, ...);
>
> extern void setup_per_cpu_pageset(void);
>
> +extern bool zone_pcp_initialized(struct zone *zone);
> extern void zone_pcp_update(struct zone *zone);
> extern void zone_pcp_reset(struct zone *zone);
>
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 3ab01b2..bc0de0f 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1013,9 +1013,13 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages, int online_typ
> * If this zone is not populated, then it is not in zonelist.
> * This means the page allocator ignores this zone.
> * So, zonelist must be updated after online.
> + *
> + * If this zone is populated, zone->pageset could be initialized
> + * to boot_pageset for the first time a node is added. If so,
> + * zone->pageset should be allocated.
> */
> mutex_lock(&zonelists_mutex);
> - if (!populated_zone(zone)) {
> + if (!populated_zone(zone) || !zone_pcp_initialized(zone)) {
> need_zonelists_rebuild = 1;
> build_all_zonelists(NULL, zone);
> }
Why does zone->present_pages of the hot-added memroy have valid value?
In my understading, the present_pages is incremented/decremented by memory
online/offline. So when hot adding memory, the zone->present_pages of the
memory should be 0.
Thanks,
Yasuaki Ishimatsu
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 736d8e1..4ff1540 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -6456,6 +6456,11 @@ void __meminit zone_pcp_update(struct zone *zone)
> }
> #endif
>
> +bool zone_pcp_initialized(struct zone *zone)
> +{
> + return (zone->pageset != &boot_pageset);
> +}
> +
> void zone_pcp_reset(struct zone *zone)
> {
> unsigned long flags;
>
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@xxxxxxxxx. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>