Re: [PATCH v1 2/2] mm/page_isolation.c: Convert SKIP_HWPOISON to MEMORY_OFFLINE

[David Hildenbrand]

On 21.10.19 17:02, Michal Hocko wrote:
> On Mon 21-10-19 16:19:26, David Hildenbrand wrote:
> > We have two types of users of page isolation:
> > 1. Memory offlining: Offline memory so it can be unplugged. Memory won't
> > 		     be touched.
> > 2. Memory allocation: Allocate memory (e.g., alloc_contig_range()) to
> > 		      become the owner of the memory and make use of it.
> >
> > For example, in case we want to offline memory, we can ignore (skip over)
> > PageHWPoison() pages, as the memory won't get used. We can allow to
> > offline memory. In contrast, we don't want to allow to allocate such
> > memory.
> >
> > Let's generalize the approach so we can special case other types of
> > pages we want to skip over in case we offline memory. While at it, also
> > pass the same flags to test_pages_isolated().
> >
> > Cc: Michal Hocko <mhocko@xxxxxxxx>
> > Cc: Oscar Salvador <osalvador@xxxxxxx>
> > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> > Cc: Anshuman Khandual <anshuman.khandual@xxxxxxx>
> > Cc: David Hildenbrand <david@xxxxxxxxxx>
> > Cc: Pingfan Liu <kernelfans@xxxxxxxxx>
> > Cc: Qian Cai <cai@xxxxxx>
> > Cc: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx>
> > Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
> > Cc: Vlastimil Babka <vbabka@xxxxxxx>
> > Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
> > Cc: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx>
> > Cc: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx>
> > Suggested-by: Michal Hocko <mhocko@xxxxxxxx>
> > Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
>
> Yes, a highlevel flag makes more sense than requesting specific types of
> pages to skip over.
>
> Acked-by: Michal Hocko <mhocko@xxxxxxxx>
>
> Please make the code easier to follow ...
> > ---
> >   include/linux/page-isolation.h |  4 ++--
> >   mm/memory_hotplug.c            |  8 +++++---
> >   mm/page_alloc.c                |  4 ++--
> >   mm/page_isolation.c            | 12 ++++++------
> >   4 files changed, 15 insertions(+), 13 deletions(-)
> >
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index bf6b21f02154..b44712c7fdd7 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -8270,7 +8270,7 @@ 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 ((flags & SKIP_HWPOISON) && PageHWPoison(page))
> > +		if (flags & MEMORY_OFFLINE && PageHWPoison(page))
> >   			continue;
> >   
> >   		if (__PageMovable(page))
> [...]
> > @@ -257,7 +258,7 @@ void undo_isolate_page_range(unsigned long start_pfn, unsigned long end_pfn,
> >    */
> >   static unsigned long
> >   __test_page_isolated_in_pageblock(unsigned long pfn, unsigned long end_pfn,
> > -				  bool skip_hwpoisoned_pages)
> > +				  int flags)
> >   {
> >   	struct page *page;
> >   
> > @@ -274,7 +275,7 @@ __test_page_isolated_in_pageblock(unsigned long pfn, unsigned long end_pfn,
> >   			 * simple way to verify that as VM_BUG_ON(), though.
> >   			 */
> >   			pfn += 1 << page_order(page);
> > -		else if (skip_hwpoisoned_pages && PageHWPoison(page))
> > +		else if (flags & MEMORY_OFFLINE && PageHWPoison(page))
> >   			/* A HWPoisoned page cannot be also PageBuddy */
> >   			pfn++;
> >   		else
>
> .. and use parentheses for the flag check.

Can do if you prefer :)

Thanks!

I'll resend both patches.

--

Thanks,

David / dhildenb