In current implementation, there are two places to isolate a range of
page: __offline_pages() and alloc_contig_range(). During this procedure,
it will drain pages on pcp list.
Below is a brief call flow:
__offline_pages()/alloc_contig_range()
start_isolate_page_range()
set_migratetype_isolate()
drain_all_pages()
drain_all_pages() <--- A
>From this snippet we can see current logic is isolate and drain pcp list
for each pageblock and drain pcp list again for the whole range.
While the drain at A is not necessary. 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. This means the procedure
to drain pages on pcp list after start_isolate_page_range() will not
drain any page in the target range.
Signed-off-by: Wei Yang <richard.weiyang@xxxxxxxxx>
---
v3:
* it is not proper to rely on caller to drain pages, so keep to drain
pages during iteration and remove the one in callers.
v2: adjust changelog with MIGRATE_ISOLATE effects for the isolated range
---
mm/memory_hotplug.c | 1 -
mm/page_alloc.c | 1 -
2 files changed, 2 deletions(-)
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 6910e0eea074..d2fa6cbbb2db 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1599,7 +1599,6 @@ static int __ref __offline_pages(unsigned long start_pfn,
cond_resched();
lru_add_drain_all();
- drain_all_pages(zone);
pfn = scan_movable_pages(start_pfn, end_pfn);
if (pfn) { /* We have movable pages */
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index f1edd36a1e2b..d9ee4bb3a1a7 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -8041,7 +8041,6 @@ int alloc_contig_range(unsigned long start, unsigned long end,
*/
lru_add_drain_all();
- drain_all_pages(cc.zone);
order = 0;
outer_start = start;
--
2.15.1
