On Fri 03-09-10 12:14:52, KAMEZAWA Hiroyuki wrote:
[...]
> ---
> include/linux/memory_hotplug.h | 1
> mm/memory_hotplug.c | 15 --------
> mm/page_alloc.c | 76 ++++++++++++++++++++++++++++++-----------
> 3 files changed, 59 insertions(+), 33 deletions(-)
>
> Index: mmotm-0827/mm/page_alloc.c
> ===================================================================
> --- mmotm-0827.orig/mm/page_alloc.c
> +++ mmotm-0827/mm/page_alloc.c
> @@ -5274,11 +5274,63 @@ void set_pageblock_flags_group(struct pa
> * page allocater never alloc memory from ISOLATE block.
> */
>
> +static int __count_unmovable_pages(struct zone *zone, struct page *page)
> +{
> + unsigned long pfn, iter, found;
> + /*
> + * For avoiding noise data, lru_add_drain_all() should be called.
> + * before this.
> + */
> + if (zone_idx(zone) == ZONE_MOVABLE)
> + return 0;
Cannot ZONE_MOVABLE contain different MIGRATE_types?
> +
> + pfn = page_to_pfn(page);
> + for (found = 0, iter = 0; iter < pageblock_nr_pages; iter++) {
> + unsigned long check = pfn + iter;
> +
> + if (!pfn_valid_within(check)) {
> + iter++;
> + continue;
> + }
> + page = pfn_to_page(check);
> + if (!page_count(page)) {
> + if (PageBuddy(page))
Why do you check page_count as well? PageBuddy has alwyas count==0,
right?
> + iter += (1 << page_order(page)) - 1;
> + continue;
> + }
> + if (!PageLRU(page))
> + found++;
> + /*
> + * If the page is not RAM, page_count()should be 0.
> + * we don't need more check. This is an _used_ not-movable page.
> + *
> + * The problematic thing here is PG_reserved pages. But if
> + * a PG_reserved page is _used_ (at boot), page_count > 1.
> + * But...is there PG_reserved && page_count(page)==0 page ?
Can we have PG_reserved && PG_lru? I also quite don't understand the
comment. At this place we are sure that the page is valid and neither
free nor LRU.
> + */
> + }
> + return found;
> +}
> +
> +bool is_pageblock_removable(struct page *page)
> +{
> + struct zone *zone = page_zone(page);
> + unsigned long flags;
> + int num;
> +
> + spin_lock_irqsave(&zone->lock, flags);
> + num = __count_unmovable_pages(zone, page);
> + spin_unlock_irqrestore(&zone->lock, flags);
Isn't this a problem? The function is triggered from userspace by sysfs
(0444 file) and holds the lock for pageblock_nr_pages. So someone can
simply read the file and block the zone->lock preventing/delaying
allocations for the rest of the system.
I think that the function should rather bail out as soon as possible.
[...]
> /* All pageblocks in the memory block are likely to be hot-removable */
> Index: mmotm-0827/include/linux/memory_hotplug.h
> ===================================================================
> --- mmotm-0827.orig/include/linux/memory_hotplug.h
> +++ mmotm-0827/include/linux/memory_hotplug.h
> @@ -76,6 +76,7 @@ extern int __add_pages(int nid, struct z
> extern int __remove_pages(struct zone *zone, unsigned long start_pfn,
> unsigned long nr_pages);
>
> +extern bool is_pageblock_removable(struct page *page);
> #ifdef CONFIG_NUMA
> extern int memory_add_physaddr_to_nid(u64 start);
> #else
Shouldn't this go rather under CONFIG_MEMORY_HOTREMOVE?
Thanks!
--
Michal Hocko
L3 team
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9
Czech Republic
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