linux-kernel - [RFC v3 2/3] mm: make optimistic check for swapin readahead

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Message-Id: <1436819284-3964-3-git-send-email-ebru.akagunduz@gmail.com>
Date:	Mon, 13 Jul 2015 23:28:03 +0300
From:	Ebru Akagunduz <ebru.akagunduz@...il.com>
To:	linux-mm@...ck.org
Cc:	akpm@...ux-foundation.org, kirill.shutemov@...ux.intel.com,
	n-horiguchi@...jp.nec.com, aarcange@...hat.com, riel@...hat.com,
	iamjoonsoo.kim@....com, xiexiuqi@...wei.com, gorcunov@...nvz.org,
	linux-kernel@...r.kernel.org, mgorman@...e.de, rientjes@...gle.com,
	vbabka@...e.cz, aneesh.kumar@...ux.vnet.ibm.com, hughd@...gle.com,
	hannes@...xchg.org, mhocko@...e.cz, boaz@...xistor.com,
	raindel@...lanox.com, Ebru Akagunduz <ebru.akagunduz@...il.com>
Subject: [RFC v3 2/3] mm: make optimistic check for swapin readahead

This patch makes optimistic check for swapin readahead
to increase thp collapse rate. Before getting swapped
out pages to memory, checks them and allows up to a
certain number. It also prints out using tracepoints
amount of unmapped ptes.

Signed-off-by: Ebru Akagunduz <ebru.akagunduz@...il.com>
---
Changes in v2:
 - Nothing changed

Changes in v3:
 - Define constant to specify exact tracepoint result (Vlastimil Babka)

 include/linux/mm.h                 |  1 +
 include/trace/events/huge_memory.h | 11 +++++++----
 mm/huge_memory.c                   | 15 ++++++++++++---
 3 files changed, 20 insertions(+), 7 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index bf341c0..eacf348 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -38,6 +38,7 @@
 #define MM_ALLOC_HUGE_PAGE_FAIL	6
 #define MM_CGROUP_CHARGE_FAIL	7
 #define MM_COLLAPSE_ISOLATE_FAIL 5
+#define MM_EXCEED_SWAP_PTE	2
 
 struct mempolicy;
 struct anon_vma;
diff --git a/include/trace/events/huge_memory.h b/include/trace/events/huge_memory.h
index cbc56fc..b6bdcc4 100644
--- a/include/trace/events/huge_memory.h
+++ b/include/trace/events/huge_memory.h
@@ -9,9 +9,9 @@
 TRACE_EVENT(mm_khugepaged_scan_pmd,
 
 	TP_PROTO(struct mm_struct *mm, struct page *page, bool writable,
-		 bool referenced, int none_or_zero, int ret),
+		 bool referenced, int none_or_zero, int ret, int unmapped),
 
-	TP_ARGS(mm, page, writable, referenced, none_or_zero, ret),
+	TP_ARGS(mm, page, writable, referenced, none_or_zero, ret, unmapped),
 
 	TP_STRUCT__entry(
 		__field(struct mm_struct *, mm)
@@ -20,6 +20,7 @@ TRACE_EVENT(mm_khugepaged_scan_pmd,
 		__field(bool, referenced)
 		__field(int, none_or_zero)
 		__field(int, ret)
+		__field(int, unmapped)
 	),
 
 	TP_fast_assign(
@@ -29,15 +30,17 @@ TRACE_EVENT(mm_khugepaged_scan_pmd,
 		__entry->referenced = referenced;
 		__entry->none_or_zero = none_or_zero;
 		__entry->ret = ret;
+		__entry->unmapped = unmapped;
 	),
 
-	TP_printk("mm=%p, page=%p, writable=%d, referenced=%d, none_or_zero=%d, ret=%d",
+	TP_printk("mm=%p, page=%p, writable=%d, referenced=%d, none_or_zero=%d, ret=%d, unmapped=%d",
 		__entry->mm,
 		__entry->page,
 		__entry->writable,
 		__entry->referenced,
 		__entry->none_or_zero,
-		__entry->ret)
+		__entry->ret,
+		__entry->unmapped)
 );
 
 TRACE_EVENT(mm_collapse_huge_page,
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 595edd9..b4cef9d 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -24,6 +24,7 @@
 #include <linux/migrate.h>
 #include <linux/hashtable.h>
 #include <linux/userfaultfd_k.h>
+#include <linux/swapops.h>
 
 #include <asm/tlb.h>
 #include <asm/pgalloc.h>
@@ -2671,11 +2672,11 @@ static int khugepaged_scan_pmd(struct mm_struct *mm,
 {
 	pmd_t *pmd;
 	pte_t *pte, *_pte;
-	int ret = 0, none_or_zero = 0;
+	int ret = 0, none_or_zero = 0, unmapped = 0;
 	struct page *page = NULL;
 	unsigned long _address;
 	spinlock_t *ptl;
-	int node = NUMA_NO_NODE;
+	int node = NUMA_NO_NODE, max_ptes_swap = HPAGE_PMD_NR/8;
 	bool writable = false, referenced = false;
 
 	VM_BUG_ON(address & ~HPAGE_PMD_MASK);
@@ -2691,6 +2692,14 @@ static int khugepaged_scan_pmd(struct mm_struct *mm,
 	for (_address = address, _pte = pte; _pte < pte+HPAGE_PMD_NR;
 	     _pte++, _address += PAGE_SIZE) {
 		pte_t pteval = *_pte;
+		if (is_swap_pte(pteval)) {
+			if (++unmapped <= max_ptes_swap) {
+				continue;
+			} else {
+				ret = MM_EXCEED_SWAP_PTE;
+				goto out_unmap;
+			}
+		}
 		if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
 			if (!userfaultfd_armed(vma) &&
 			    ++none_or_zero <= khugepaged_max_ptes_none) {
@@ -2755,7 +2764,7 @@ out_unmap:
 	}
 out:
 	trace_mm_khugepaged_scan_pmd(mm, page, writable, referenced,
-				     none_or_zero, ret);
+				     none_or_zero, ret, unmapped);
 	return ret;
 }
 
-- 
1.9.1

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