The min wmark should be satisfied with just 1 hugepage. And the other
wmarks should be adjusted accordingly. We need to succeed the low
wmark check if there's some significant amount of 0 order pages, but
we don't need plenty of high order pages because the PF_MEMALLOC paths
don't require those. Creating a ton of high order pages that cannot be
allocated by the high order allocation paths (no PF_MEMALLOC) is quite
wasteful because they can be splitted in lower order pages before
anybody has a chance to allocate them.
Signed-off-by: Andrea Arcangeli <aarcange@xxxxxxxxxx>
---
mm/page_alloc.c | 17 +++++++++++++++++
1 file changed, 17 insertions(+)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 092b30d..4401983 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1643,6 +1643,23 @@ static bool __zone_watermark_ok(struct zone *z, int order, unsigned long mark,
if (free_pages - free_cma <= min + lowmem_reserve)
return false;
+ if (!order)
+ return true;
+
+ /*
+ * Don't require any high order page under the min
+ * wmark. Invoking compaction to create lots of high order
+ * pages below the min wmark is wasteful because those
+ * hugepages cannot be allocated without PF_MEMALLOC and the
+ * PF_MEMALLOC paths must not depend on high order allocations
+ * to succeed.
+ */
+ min = mark - z->watermark[WMARK_MIN];
+ WARN_ON(min < 0);
+ if (alloc_flags & ALLOC_HIGH)
+ min -= min / 2;
+ if (alloc_flags & ALLOC_HARDER)
+ min -= min / 4;
for (o = 0; o < order; o++) {
/* At the next order, this order's pages become unavailable */
free_pages -= z->free_area[o].nr_free << o;
--
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