linux-kernel - [RFC 3/6] mm, thp: try fault allocations only if we expect them to succeed

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Date:	Mon, 23 Feb 2015 13:58:39 +0100
From:	Vlastimil Babka <vbabka@...e.cz>
To:	linux-mm@...ck.org
Cc:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Hugh Dickins <hughd@...gle.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Rik van Riel <riel@...hat.com>, Mel Gorman <mgorman@...e.de>,
	Michal Hocko <mhocko@...e.cz>,
	Ebru Akagunduz <ebru.akagunduz@...il.com>,
	Alex Thorlton <athorlton@....com>,
	David Rientjes <rientjes@...gle.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	Vlastimil Babka <vbabka@...e.cz>
Subject: [RFC 3/6] mm, thp: try fault allocations only if we expect them to succeed

Since we check THP availability for khugepaged THP collapses, we can use it
also for page fault THP allocations. If khugepaged with its sync compaction
is not able to allocate a hugepage, then it's unlikely that the less involved
attempt on page fault would succeed.

Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
---
 mm/huge_memory.c | 39 ++++++++++++++++++++++++++++++---------
 1 file changed, 30 insertions(+), 9 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 55846b8..1eec1a6 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -761,6 +761,32 @@ static inline gfp_t alloc_hugepage_gfpmask(int defrag)
 	return (GFP_TRANSHUGE & ~(defrag ? 0 : __GFP_WAIT));
 }
 
+//TODO: inline? check bloat-o-meter
+static inline struct page *
+fault_alloc_hugepage(struct vm_area_struct *vma, unsigned long haddr)
+{
+	struct page *hpage;
+	gfp_t gfp;
+	int nid;
+
+	nid = numa_node_id();
+	/*
+	 * This check is not exact for interleave policy, but we can leave such
+	 * cases to later scanning.
+	 * TODO: should VM_HUGEPAGE madvised vma's proceed regardless of the check?
+	 */
+	if (!node_isset(nid, thp_avail_nodes))
+		return NULL;
+
+	gfp = alloc_hugepage_gfpmask(transparent_hugepage_defrag(vma));
+	hpage = alloc_hugepage_vma(gfp, vma, haddr, HPAGE_PMD_ORDER);
+
+	if (!hpage)
+		node_clear(nid, thp_avail_nodes);
+
+	return hpage;
+}
+
 /* Caller must hold page table lock. */
 static bool set_huge_zero_page(pgtable_t pgtable, struct mm_struct *mm,
 		struct vm_area_struct *vma, unsigned long haddr, pmd_t *pmd,
@@ -781,7 +807,6 @@ int do_huge_pmd_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma,
 			       unsigned long address, pmd_t *pmd,
 			       unsigned int flags)
 {
-	gfp_t gfp;
 	struct page *page;
 	unsigned long haddr = address & HPAGE_PMD_MASK;
 
@@ -816,8 +841,7 @@ int do_huge_pmd_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma,
 		}
 		return 0;
 	}
-	gfp = alloc_hugepage_gfpmask(transparent_hugepage_defrag(vma));
-	page = alloc_hugepage_vma(gfp, vma, haddr, HPAGE_PMD_ORDER);
+	page = fault_alloc_hugepage(vma, haddr);
 	if (unlikely(!page)) {
 		count_vm_event(THP_FAULT_FALLBACK);
 		return VM_FAULT_FALLBACK;
@@ -1105,12 +1129,9 @@ int do_huge_pmd_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
 	spin_unlock(ptl);
 alloc:
 	if (transparent_hugepage_enabled(vma) &&
-	    !transparent_hugepage_debug_cow()) {
-		gfp_t gfp;
-
-		gfp = alloc_hugepage_gfpmask(transparent_hugepage_defrag(vma));
-		new_page = alloc_hugepage_vma(gfp, vma, haddr, HPAGE_PMD_ORDER);
-	} else
+	    !transparent_hugepage_debug_cow())
+		new_page = fault_alloc_hugepage(vma, haddr);
+	else
 		new_page = NULL;
 
 	if (unlikely(!new_page)) {
-- 
2.1.4

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