On 09/06/2012 10:53 AM, Minchan Kim wrote:
> Normally, MIGRATE_ISOLATE type is used for memory-hotplug.
> But it's irony type because the pages isolated would exist
> as free page in free_area->free_list[MIGRATE_ISOLATE] so people
> can think of it as allocatable pages but it is *never* allocatable.
> It ends up confusing NR_FREE_PAGES vmstat so it would be
> totally not accurate so some of place which depend on such vmstat
> could reach wrong decision by the context.
>
> There were already report about it.[1]
> [1] 702d1a6e, memory-hotplug: fix kswapd looping forever problem
>
> Then, there was other report which is other problem.[2]
> [2] http://www.spinics.net/lists/linux-mm/msg41251.html
>
> I believe it can make problems in future, too.
> So I hope removing such irony type by another design.
>
> I hope this patch solves it and let's revert [1] and doesn't need [2].
>
> * Changelog v1
> * Fix from Michal's many suggestion
>
> Cc: Michal Nazarewicz <min...@mina86.com>
> Cc: Mel Gorman <m...@csn.ul.ie>
> Cc: Kamezawa Hiroyuki <kamezawa.hir...@jp.fujitsu.com>
> Cc: Yasuaki Ishimatsu <isimatu.yasu...@jp.fujitsu.com>
> Cc: Wen Congyang <we...@cn.fujitsu.com>
> Cc: Konrad Rzeszutek Wilk <konrad.w...@oracle.com>
> Signed-off-by: Minchan Kim <minc...@kernel.org>
> ---
> @@ -180,30 +287,35 @@ int undo_isolate_page_range(unsigned long start_pfn,
> unsigned long end_pfn,
> * all pages in [start_pfn...end_pfn) must be in the same zone.
> * zone->lock must be held before call this.
> *
> - * Returns 1 if all pages in the range are isolated.
> + * Returns true if all pages in the range are isolated.
> */
> -static int
> -__test_page_isolated_in_pageblock(unsigned long pfn, unsigned long end_pfn)
> +static bool
> +__test_page_isolated_in_pageblock(unsigned long start_pfn, unsigned long
> end_pfn)
> {
> + unsigned long pfn, next_pfn;
> struct page *page;
>
> - while (pfn < end_pfn) {
> - if (!pfn_valid_within(pfn)) {
> - pfn++;
> - continue;
> - }
> - page = pfn_to_page(pfn);
> - if (PageBuddy(page))
> - pfn += 1 << page_order(page);
> - else if (page_count(page) == 0 &&
> - page_private(page) == MIGRATE_ISOLATE)
> - pfn += 1;
> - else
> - break;
> + list_for_each_entry(page, &isolated_pages, lru) {
> + if (&page->lru == &isolated_pages)
> + return false;
what's the mean of this line?
> + pfn = page_to_pfn(page);
> + if (pfn >= end_pfn)
> + return false;
> + if (pfn >= start_pfn)
> + goto found;
> + }
> + return false;
> +
> + list_for_each_entry_continue(page, &isolated_pages, lru) {
> + if (page_to_pfn(page) != next_pfn)
> + return false;
where is next_pfn init-ed?
> +found:
> + pfn = page_to_pfn(page);
> + next_pfn = pfn + (1UL << page_order(page));
> + if (next_pfn >= end_pfn)
> + return true;
> }
> - if (pfn < end_pfn)
> - return 0;
> - return 1;
> + return false;
> }
>
> int test_pages_isolated(unsigned long start_pfn, unsigned long end_pfn)
> @@ -211,7 +323,7 @@ int test_pages_isolated(unsigned long start_pfn, unsigned
> long end_pfn)
> unsigned long pfn, flags;
> struct page *page;
> struct zone *zone;
> - int ret;
> + bool ret;
>
> /*
> * Note: pageblock_nr_page != MAX_ORDER. Then, chunks of free page
> diff --git a/mm/vmstat.c b/mm/vmstat.c
> index df7a674..bb59ff7 100644
> --- a/mm/vmstat.c
> +++ b/mm/vmstat.c
> @@ -616,7 +616,6 @@ static char * const migratetype_names[MIGRATE_TYPES] = {
> #ifdef CONFIG_CMA
> "CMA",
> #endif
> - "Isolate",
> };
>
> static void *frag_start(struct seq_file *m, loff_t *pos)
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