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SubjectRe: [RFC] memory hotremove patch take 2 [04/10] (isolate all free pages)
On Wed, 9 May 2007, Yasunori Goto wrote:

> Isolate all freed pages (means in buddy_list) in the range.
> See page_buddy() and free_one_page() function if unsure.
>
> Signed-Off-By: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> Signed-off-by: Yasunori Goto <y-goto@jp.fujitsu.com>
>
> include/linux/page_isolation.h | 1
> mm/page_alloc.c | 45 +++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 46 insertions(+)
>
> Index: current_test/mm/page_alloc.c
> ===================================================================
> --- current_test.orig/mm/page_alloc.c 2007-05-08 15:08:04.000000000 +0900
> +++ current_test/mm/page_alloc.c 2007-05-08 15:08:26.000000000 +0900
> @@ -4411,6 +4411,51 @@ free_all_isolated_pages(struct isolation
> }
> }
>
> +/*
> + * Isolate already freed pages.
> + */
> +int
> +capture_isolate_freed_pages(struct isolation_info *info)
> +{
> + struct zone *zone;
> + unsigned long pfn;
> + struct page *page;
> + int order, order_size;
> + int nr_pages = 0;
> + unsigned long last_pfn = info->end_pfn - 1;
> + pfn = info->start_pfn;
> + if (!pfn_valid(pfn))
> + return -EINVAL;

This may lead to boundary cases where pages cannot be captured at the
start and end of non-aligned zones due to memory holes.

> + zone = info->zone;
> + if ((zone != page_zone(pfn_to_page(pfn))) ||
> + (zone != page_zone(pfn_to_page(last_pfn))))
> + return -EINVAL;

Is this check really necessary? Surely a caller to
capture_isolate_freed_pages() will have already made all the necessary
checks when adding the struct insolation_info ?

> + drain_all_pages();
> + spin_lock(&zone->lock);
> + while (pfn < info->end_pfn) {
> + if (!pfn_valid(pfn)) {
> + pfn++;
> + continue;
> + }
> + page = pfn_to_page(pfn);
> + /* See page_is_buddy() */
> + if (page_count(page) == 0 && PageBuddy(page)) {

If PageBuddy is set it's free, you shouldn't have to check the page_count.

> + order = page_order(page);
> + order_size = 1 << order;
> + zone->free_area[order].nr_free--;
> + __mod_zone_page_state(zone, NR_FREE_PAGES, -order_size);
> + list_del(&page->lru);
> + rmv_page_order(page);
> + isolate_page_nolock(info, page, order);
> + nr_pages += order_size;
> + pfn += order_size;
> + } else {
> + pfn++;
> + }
> + }
> + spin_unlock(&zone->lock);
> + return nr_pages;
> +}
> #endif /* CONFIG_PAGE_ISOLATION */
>

This is all similar to move_freepages() other than the locking part. It
would be worth checking if there is code that could be shared or at least
have similar styles.

>
> Index: current_test/include/linux/page_isolation.h
> ===================================================================
> --- current_test.orig/include/linux/page_isolation.h 2007-05-08 15:08:04.000000000 +0900
> +++ current_test/include/linux/page_isolation.h 2007-05-08 15:08:27.000000000 +0900
> @@ -40,6 +40,7 @@ extern void free_isolation_info(struct i
> extern void unuse_all_isolated_pages(struct isolation_info *info);
> extern void free_all_isolated_pages(struct isolation_info *info);
> extern void drain_all_pages(void);
> +extern int capture_isolate_freed_pages(struct isolation_info *info);
>
> #else
>
>
> --
> Yasunori Goto
>
>

--
Mel Gorman
Part-time Phd Student Linux Technology Center
University of Limerick IBM Dublin Software Lab
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