On Tue, Dec 18, 2018 at 10:14:25PM +0100, David Hildenbrand wrote: >On 18.12.18 21:46, Wei Yang wrote: >> Below is a brief call flow for __offline_pages() and >> alloc_contig_range(): >> >> __offline_pages()/alloc_contig_range() >> start_isolate_page_range() >> set_migratetype_isolate() >> drain_all_pages() >> drain_all_pages() >> >> Current logic is: isolate and drain pcp list for each pageblock and >> drain pcp list again. This is not necessary and we could just drain pcp >> list once after isolate this whole range. >> >> The reason is start_isolate_page_range() will set the migrate type of >> a range to MIGRATE_ISOLATE. After doing so, this range will never be >> allocated from Buddy, neither to a real user nor to pcp list. >> >> Since drain_all_pages() is zone based, by reduce times of >> drain_all_pages() also reduce some contention on this particular zone. >> >> Signed-off-by: Wei Yang <richard.weiyang@xxxxxxxxx> > >Yes, as far as I can see, when a MIGRATE_ISOLATE page gets freed, it >will not go onto the pcp list again. > >However, start_isolate_page_range() is also called via >alloc_contig_range(). Are you sure we can effectively drop the >drain_all_pages() for that call path? > alloc_contig_range() does following now: - isolate page range - do reclaim and migration - drain lru - drain pcp list If step 2 fails, it will not drain lru and pcp list. I don't see we have to drain pcp list before step 2. And after this change, it will save some effort if step 2 fails. >> >> --- >> v2: adjust changelog with MIGRATE_ISOLATE effects for the isolated range >> --- >> mm/page_isolation.c | 2 -- >> 1 file changed, 2 deletions(-) >> >> diff --git a/mm/page_isolation.c b/mm/page_isolation.c >> index 43e085608846..f44c0e333bed 100644 >> --- a/mm/page_isolation.c >> +++ b/mm/page_isolation.c >> @@ -83,8 +83,6 @@ static int set_migratetype_isolate(struct page *page, int migratetype, >> } >> >> spin_unlock_irqrestore(&zone->lock, flags); >> - if (!ret) >> - drain_all_pages(zone); >> return ret; >> } >> >> > > >-- > >Thanks, > >David / dhildenb -- Wei Yang Help you, Help me
