mm: compaction: partially revert capture of suitable high-order page
Eric Wong reported on 3.7 and 3.8-rc2 that ppoll() got stuck when
waiting for POLLIN on a local TCP socket. It was easier to trigger if
there was disk IO and dirty pages at the same time and he bisected it to
commit 1fb3f8ca0e92 ("mm: compaction: capture a suitable high-order page
immediately when it is made available").
The intention of that patch was to improve high-order allocations under
memory pressure after changes made to reclaim in 3.6 drastically hurt
THP allocations but the approach was flawed. For Eric, the problem was
that page->pfmemalloc was not being cleared for captured pages leading
to a poor interaction with swap-over-NFS support causing the packets to
be dropped. However, I identified a few more problems with the patch
including the fact that it can increase contention on zone->lock in some
cases which could result in async direct compaction being aborted early.
In retrospect the capture patch took the wrong approach. What it should
have done is mark the pageblock being migrated as MIGRATE_ISOLATE if it
was allocating for THP and avoided races that way. While the patch was
showing to improve allocation success rates at the time, the benefit is
marginal given the relative complexity and it should be revisited from
scratch in the context of the other reclaim-related changes that have
taken place since the patch was first written and tested. This patch
partially reverts commit 1fb3f8ca0e92 ("mm: compaction: capture a
suitable high-order page immediately when it is made available").
Change-Id: I985725a72aac0fdecbf4310c04d176f39e0386dd
Reported-and-tested-by: Eric Wong <normalperson@yhbt.net>
Tested-by: Eric Dumazet <eric.dumazet@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Mel Gorman <mgorman@suse.de>
Cc: David Miller <davem@davemloft.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Git-commit: 8fb74b9fb2b182d54beee592350d9ea1f325917a
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
Signed-off-by: Laura Abbott <lauraa@codeaurora.org>
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index ca215b3..5148c1a 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1441,14 +1441,8 @@
set_page_refcounted(page + i);
}
-/*
- * Similar to the split_page family of functions except that the page
- * required at the given order and being isolated now to prevent races
- * with parallel allocators
- */
-int capture_free_page(struct page *page, int alloc_order, int migratetype)
+static int __isolate_free_page(struct page *page, unsigned int order)
{
- unsigned int order;
unsigned long watermark;
struct zone *zone;
int mt;
@@ -1456,7 +1450,6 @@
BUG_ON(!PageBuddy(page));
zone = page_zone(page);
- order = page_order(page);
mt = get_pageblock_migratetype(page);
if (mt != MIGRATE_ISOLATE && !is_migrate_cma(mt)) {
@@ -1465,7 +1458,7 @@
if (!zone_watermark_ok(zone, 0, watermark, 0, 0))
return 0;
- __mod_zone_freepage_state(zone, -(1UL << alloc_order), mt);
+ __mod_zone_freepage_state(zone, -(1UL << order), mt);
}
/* Remove page from free list */
@@ -1473,11 +1466,7 @@
zone->free_area[order].nr_free--;
rmv_page_order(page);
- if (alloc_order != order)
- expand(zone, page, alloc_order, order,
- &zone->free_area[order], migratetype);
-
- /* Set the pageblock if the captured page is at least a pageblock */
+ /* Set the pageblock if the isolated page is at least a pageblock */
if (order >= pageblock_order - 1) {
struct page *endpage = page + (1 << order) - 1;
for (; page < endpage; page += pageblock_nr_pages) {
@@ -1506,10 +1495,9 @@
unsigned int order;
int nr_pages;
- BUG_ON(!PageBuddy(page));
order = page_order(page);
- nr_pages = capture_free_page(page, order, 0);
+ nr_pages = __isolate_free_page(page, order);
if (!nr_pages)
return 0;
@@ -2161,8 +2149,6 @@
bool *contended_compaction, bool *deferred_compaction,
unsigned long *did_some_progress)
{
- struct page *page = NULL;
-
if (!order)
return NULL;
@@ -2174,16 +2160,12 @@
current->flags |= PF_MEMALLOC;
*did_some_progress = try_to_compact_pages(zonelist, order, gfp_mask,
nodemask, sync_migration,
- contended_compaction, &page);
+ contended_compaction);
current->flags &= ~PF_MEMALLOC;
- /* If compaction captured a page, prep and use it */
- if (page) {
- prep_new_page(page, order, gfp_mask);
- goto got_page;
- }
-
if (*did_some_progress != COMPACT_SKIPPED) {
+ struct page *page;
+
/* Page migration frees to the PCP lists but we want merging */
drain_pages(get_cpu());
put_cpu();
@@ -2193,7 +2175,6 @@
alloc_flags, preferred_zone,
migratetype);
if (page) {
-got_page:
preferred_zone->compact_blockskip_flush = false;
preferred_zone->compact_considered = 0;
preferred_zone->compact_defer_shift = 0;