Re: [-next] lots of messages due to "mm, memory_hotplug: be more verbose for memory offline failures"

[Michal Hocko]

On Tue 18-12-18 08:55:38, Heiko Carstens wrote:
> On Mon, Dec 17, 2018 at 05:39:49PM +0100, Michal Hocko wrote:
> > On Mon 17-12-18 17:03:50, Michal Hocko wrote:
> > > On Mon 17-12-18 16:59:22, Heiko Carstens wrote:
> > > > Hi Michal,
> > > > 
> > > > with linux-next as of today on s390 I see tons of messages like
> > > > 
> > > > [   20.536664] page dumped because: has_unmovable_pages
> > > > [   20.536792] page:000003d081ff4080 count:1 mapcount:0 mapping:000000008ff88600 index:0x0 compound_mapcount: 0
> > > > [   20.536794] flags: 0x3fffe0000010200(slab|head)
> > > > [   20.536795] raw: 03fffe0000010200 0000000000000100 0000000000000200 000000008ff88600
> > > > [   20.536796] raw: 0000000000000000 0020004100000000 ffffffff00000001 0000000000000000
> > > > [   20.536797] page dumped because: has_unmovable_pages
> > > > [   20.536814] page:000003d0823b0000 count:1 mapcount:0 mapping:0000000000000000 index:0x0
> > > > [   20.536815] flags: 0x7fffe0000000000()
> > > > [   20.536817] raw: 07fffe0000000000 0000000000000100 0000000000000200 0000000000000000
> > > > [   20.536818] raw: 0000000000000000 0000000000000000 ffffffff00000001 0000000000000000
> > > > 
> > > > bisect points to b323c049a999 ("mm, memory_hotplug: be more verbose for memory offline failures")
> > > > which is the first commit with which the messages appear.
> > > 
> > > I would bet this is CMA allocator. How much is tons? Maybe we want a
> > > rate limit or the other user is not really interested in them at all?
> 
> Yes, the system in question has a 4NB CMA area. "tons" translates to several hundred.

OK, I guess these messages on their own without a wider context are not
that helpful. It is still surprising to see slab pages or non-movable
pages in the CMA area. The later might be an CMA allocation I guess but
slab pages shouldn't be there at all AFAIU.
 
> > In other words, this should silence those messages.
> 
> Yes, with the patch below applied the messages don't appear anymore.

OK, I will post an official patch. Even if CMA allocator decides to
report failures it can simply add the flag.

Thanks!

> > diff --git a/include/linux/page-isolation.h b/include/linux/page-isolation.h
> > index 4ae347cbc36d..4eb26d278046 100644
> > --- a/include/linux/page-isolation.h
> > +++ b/include/linux/page-isolation.h
> > @@ -30,8 +30,11 @@ static inline bool is_migrate_isolate(int migratetype)
> >  }
> >  #endif
> > 
> > +#define SKIP_HWPOISON	0x1
> > +#define REPORT_FAILURE	0x2
> > +
> >  bool has_unmovable_pages(struct zone *zone, struct page *page, int count,
> > -			 int migratetype, bool skip_hwpoisoned_pages);
> > +			 int migratetype, int flags);
> >  void set_pageblock_migratetype(struct page *page, int migratetype);
> >  int move_freepages_block(struct zone *zone, struct page *page,
> >  				int migratetype, int *num_movable);
> > @@ -44,10 +47,14 @@ int move_freepages_block(struct zone *zone, struct page *page,
> >   * For isolating all pages in the range finally, the caller have to
> >   * free all pages in the range. test_page_isolated() can be used for
> >   * test it.
> > + *
> > + * The following flags are allowed (they can be combined in a bit mask)
> > + * SKIP_HWPOISON - ignore hwpoison pages
> > + * REPORT_FAILURE - report details about the failure to isolate the range
> >   */
> >  int
> >  start_isolate_page_range(unsigned long start_pfn, unsigned long end_pfn,
> > -			 unsigned migratetype, bool skip_hwpoisoned_pages);
> > +			 unsigned migratetype, int flags);
> > 
> >  /*
> >   * Changes MIGRATE_ISOLATE to MIGRATE_MOVABLE.
> > diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> > index c82193db4be6..8537429d33a6 100644
> > --- a/mm/memory_hotplug.c
> > +++ b/mm/memory_hotplug.c
> > @@ -1226,7 +1226,7 @@ static bool is_pageblock_removable_nolock(struct page *page)
> >  	if (!zone_spans_pfn(zone, pfn))
> >  		return false;
> > 
> > -	return !has_unmovable_pages(zone, page, 0, MIGRATE_MOVABLE, true);
> > +	return !has_unmovable_pages(zone, page, 0, MIGRATE_MOVABLE, SKIP_HWPOISON);
> >  }
> > 
> >  /* Checks if this range of memory is likely to be hot-removable. */
> > @@ -1577,7 +1577,8 @@ static int __ref __offline_pages(unsigned long start_pfn,
> > 
> >  	/* set above range as isolated */
> >  	ret = start_isolate_page_range(start_pfn, end_pfn,
> > -				       MIGRATE_MOVABLE, true);
> > +				       MIGRATE_MOVABLE,
> > +				       SKIP_HWPOISON | REPORT_FAILURE);
> >  	if (ret) {
> >  		mem_hotplug_done();
> >  		reason = "failure to isolate range";
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index ec2c7916dc2d..ee4043419791 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -7754,8 +7754,7 @@ void *__init alloc_large_system_hash(const char *tablename,
> >   * race condition. So you can't expect this function should be exact.
> >   */
> >  bool has_unmovable_pages(struct zone *zone, struct page *page, int count,
> > -			 int migratetype,
> > -			 bool skip_hwpoisoned_pages)
> > +			 int migratetype, int flags)
> >  {
> >  	unsigned long pfn, iter, found;
> > 
> > @@ -7818,7 +7817,7 @@ bool has_unmovable_pages(struct zone *zone, struct page *page, int count,
> >  		 * The HWPoisoned page may be not in buddy system, and
> >  		 * page_count() is not 0.
> >  		 */
> > -		if (skip_hwpoisoned_pages && PageHWPoison(page))
> > +		if ((flags & SKIP_HWPOISON) && PageHWPoison(page))
> >  			continue;
> > 
> >  		if (__PageMovable(page))
> > @@ -7845,7 +7844,8 @@ bool has_unmovable_pages(struct zone *zone, struct page *page, int count,
> >  	return false;
> >  unmovable:
> >  	WARN_ON_ONCE(zone_idx(zone) == ZONE_MOVABLE);
> > -	dump_page(pfn_to_page(pfn+iter), "unmovable page");
> > +	if (flags & REPORT_FAILURE)
> > +		dump_page(pfn_to_page(pfn+iter), "unmovable page");
> >  	return true;
> >  }
> > 
> > @@ -7972,8 +7972,7 @@ int alloc_contig_range(unsigned long start, unsigned long end,
> >  	 */
> > 
> >  	ret = start_isolate_page_range(pfn_max_align_down(start),
> > -				       pfn_max_align_up(end), migratetype,
> > -				       false);
> > +				       pfn_max_align_up(end), migratetype, 0);
> >  	if (ret)
> >  		return ret;
> > 
> > diff --git a/mm/page_isolation.c b/mm/page_isolation.c
> > index 43e085608846..ce323e56b34d 100644
> > --- a/mm/page_isolation.c
> > +++ b/mm/page_isolation.c
> > @@ -15,8 +15,7 @@
> >  #define CREATE_TRACE_POINTS
> >  #include <trace/events/page_isolation.h>
> > 
> > -static int set_migratetype_isolate(struct page *page, int migratetype,
> > -				bool skip_hwpoisoned_pages)
> > +static int set_migratetype_isolate(struct page *page, int migratetype, int isol_flags)
> >  {
> >  	struct zone *zone;
> >  	unsigned long flags, pfn;
> > @@ -60,8 +59,7 @@ static int set_migratetype_isolate(struct page *page, int migratetype,
> >  	 * FIXME: Now, memory hotplug doesn't call shrink_slab() by itself.
> >  	 * We just check MOVABLE pages.
> >  	 */
> > -	if (!has_unmovable_pages(zone, page, arg.pages_found, migratetype,
> > -				 skip_hwpoisoned_pages))
> > +	if (!has_unmovable_pages(zone, page, arg.pages_found, migratetype, flags))
> >  		ret = 0;
> > 
> >  	/*
> > @@ -185,7 +183,7 @@ __first_valid_page(unsigned long pfn, unsigned long nr_pages)
> >   * prevents two threads from simultaneously working on overlapping ranges.
> >   */
> >  int start_isolate_page_range(unsigned long start_pfn, unsigned long end_pfn,
> > -			     unsigned migratetype, bool skip_hwpoisoned_pages)
> > +			     unsigned migratetype, int flags)
> >  {
> >  	unsigned long pfn;
> >  	unsigned long undo_pfn;
> > @@ -199,7 +197,7 @@ int start_isolate_page_range(unsigned long start_pfn, unsigned long end_pfn,
> >  	     pfn += pageblock_nr_pages) {
> >  		page = __first_valid_page(pfn, pageblock_nr_pages);
> >  		if (page &&
> > -		    set_migratetype_isolate(page, migratetype, skip_hwpoisoned_pages)) {
> > +		    set_migratetype_isolate(page, migratetype, flags)) {
> >  			undo_pfn = pfn;
> >  			goto undo;
> >  		}
> > -- 
> > Michal Hocko
> > SUSE Labs
> > 

-- 
Michal Hocko
SUSE Labs