Re: [PATCH] mm, memory_hotplug: teach has_unmovable_pages about of LRU migrateable pages

[Baoquan He <bhe@redhat.com>]

Hi Michal,

On 11/02/18 at 04:55pm, Michal Hocko wrote:
> From: Michal Hocko <mhocko@suse.com>
> 
> Baoquan He has noticed that 15c30bc09085  ("mm, memory_hotplug: make
> has_unmovable_pages more robust") is causing memory offlining failures
> on a movable node. After a further debugging it turned out that
> has_unmovable_pages fails prematurely because it stumbles over off-LRU
> pages. Nevertheless those pages are not on LRU because they are waiting
> on the pcp LRU caches (an example of __dump_page added by a debugging
> patch)
> [  560.923297] page:ffffea043f39fa80 count:1 mapcount:0 mapping:ffff880e5dce1b59 index:0x7f6eec459
> [  560.931967] flags: 0x5fffffc0080024(uptodate|active|swapbacked)
> [  560.937867] raw: 005fffffc0080024 dead000000000100 dead000000000200 ffff880e5dce1b59
> [  560.945606] raw: 00000007f6eec459 0000000000000000 00000001ffffffff ffff880e43ae8000
> [  560.953323] page dumped because: hotplug
> [  560.957238] page->mem_cgroup:ffff880e43ae8000
> [  560.961620] has_unmovable_pages: pfn:0x10fd030d, found:0x1, count:0x0
> [  560.968127] page:ffffea043f40c340 count:2 mapcount:0 mapping:ffff880e2f2d8628 index:0x0
> [  560.976104] flags: 0x5fffffc0000006(referenced|uptodate)
> [  560.981401] raw: 005fffffc0000006 dead000000000100 dead000000000200 ffff880e2f2d8628
> [  560.989119] raw: 0000000000000000 0000000000000000 00000002ffffffff ffff88010a8f5000
> [  560.996833] page dumped because: hotplug

Sorry, last week I didn't test this patch with memory pressure adding.
Today use "stress -m 200 -t 2h" to add pressure, hot removing failed.
Will send you output log. W/o memory pressure, it sometimes succeed. I
saw one failure last night, it still show un-removable as 0 in
hotpluggable node one time, I worried it might be caused by my compiling
mistake, so compile and try again this morning.

Thanks
Baoquan