On 09/06/2012 04:18 PM, Minchan Kim wrote:
> Hello Lai,
>
> On Thu, Sep 06, 2012 at 04:14:51PM +0800, Lai Jiangshan wrote:
>> 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?
>
> I just copied it from Michal's code but It seem to be not needed.
> I will remove it in next spin.
>
>>
>>> + pfn = page_to_pfn(page);
>>> + if (pfn >= end_pfn)
>>> + return false;
>>> + if (pfn >= start_pfn)
>>> + goto found;
this test is wrong.
if ((pfn <= start_pfn) && (start_pfn < pfn + (1UL << page_order(page))))
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?
>
> by "goto found"
don't goto inner label.
move the found label up:
+
+found:
+ next_pfn = page_to_pfn(page);
+ list_for_each_entry_from(page, &isolated_pages, lru) {
+ if (page_to_pfn(page) != next_pfn)
+ return false;
+ pfn = page_to_pfn(page);
+ next_pfn = pfn + (1UL << page_order(page));
+ if (next_pfn >= end_pfn)
+ return true;
}
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