mm: remove per-zone hashtable of bitlock waitqueues

The per-zone waitqueues exist because of a scalability issue with the
page waitqueues on some NUMA machines, but it turns out that they hurt
normal loads, and now with the vmalloced stacks they also end up
breaking gfs2 that uses a bit_wait on a stack object:

     wait_on_bit(&gh->gh_iflags, HIF_WAIT, TASK_UNINTERRUPTIBLE)

where 'gh' can be a reference to the local variable 'mount_gh' on the
stack of fill_super().

The reason the per-zone hash table breaks for this case is that there is
no "zone" for virtual allocations, and trying to look up the physical
page to get at it will fail (with a BUG_ON()).

It turns out that I actually complained to the mm people about the
per-zone hash table for another reason just a month ago: the zone lookup
also hurts the regular use of "unlock_page()" a lot, because the zone
lookup ends up forcing several unnecessary cache misses and generates
horrible code.

As part of that earlier discussion, we had a much better solution for
the NUMA scalability issue - by just making the page lock have a
separate contention bit, the waitqueue doesn't even have to be looked at
for the normal case.

Peter Zijlstra already has a patch for that, but let's see if anybody
even notices.  In the meantime, let's fix the actual gfs2 breakage by
simplifying the bitlock waitqueues and removing the per-zone issue.

Reported-by: Andreas Gruenbacher <agruenba@redhat.com>
Tested-by: Bob Peterson <rpeterso@redhat.com>
Acked-by: Mel Gorman <mgorman@techsingularity.net>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Steven Whitehouse <swhiteho@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 0 insertions, 28 deletions

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 962927309b6e..b18dab401be6 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -268,7 +268,6 @@ void __init register_page_bootmem_info_node(struct pglist_data *pgdat)
 	unsigned long i, pfn, end_pfn, nr_pages;
 	int node = pgdat->node_id;
 	struct page *page;
-	struct zone *zone;
 
 	nr_pages = PAGE_ALIGN(sizeof(struct pglist_data)) >> PAGE_SHIFT;
 	page = virt_to_page(pgdat);
@@ -276,19 +275,6 @@ void __init register_page_bootmem_info_node(struct pglist_data *pgdat)
 	for (i = 0; i < nr_pages; i++, page++)
 		get_page_bootmem(node, page, NODE_INFO);
 
-	zone = &pgdat->node_zones[0];
-	for (; zone < pgdat->node_zones + MAX_NR_ZONES - 1; zone++) {
-		if (zone_is_initialized(zone)) {
-			nr_pages = zone->wait_table_hash_nr_entries
-				* sizeof(wait_queue_head_t);
-			nr_pages = PAGE_ALIGN(nr_pages) >> PAGE_SHIFT;
-			page = virt_to_page(zone->wait_table);
-
-			for (i = 0; i < nr_pages; i++, page++)
-				get_page_bootmem(node, page, NODE_INFO);
-		}
-	}
-
 	pfn = pgdat->node_start_pfn;
 	end_pfn = pgdat_end_pfn(pgdat);
 
@@ -2158,20 +2144,6 @@ void try_offline_node(int nid)
 	 */
 	node_set_offline(nid);
 	unregister_one_node(nid);
-
-	/* free waittable in each zone */
-	for (i = 0; i < MAX_NR_ZONES; i++) {
-		struct zone *zone = pgdat->node_zones + i;
-
-		/*
-		 * wait_table may be allocated from boot memory,
-		 * here only free if it's allocated by vmalloc.
-		 */
-		if (is_vmalloc_addr(zone->wait_table)) {
-			vfree(zone->wait_table);
-			zone->wait_table = NULL;
-		}
-	}
 }
 EXPORT_SYMBOL(try_offline_node);