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Date:   Tue, 18 Feb 2020 18:29:18 -0800 (PST)
From:   David Rientjes <rientjes@google.com>
To:     Andrew Morton <akpm@linux-foundation.org>
cc:     "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Mike Rapoport <rppt@linux.ibm.com>,
        Jeremy Cline <jcline@redhat.com>, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org
Subject: [patch 1/2] mm, shmem: add thp fault alloc and fallback stats
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The thp_fault_alloc and thp_fault_fallback vmstats are incremented when a
hugepage is successfully or unsuccessfully allocated, respectively, during
a page fault for anonymous memory.

Extend this to shmem as well.  Note that care is taken to increment
thp_fault_alloc only when the fault succeeds; this is the same behavior as
anonymous thp.

Signed-off-by: David Rientjes <rientjes@google.com>
---
 mm/shmem.c | 23 ++++++++++++++---------
 1 file changed, 14 insertions(+), 9 deletions(-)

diff --git a/mm/shmem.c b/mm/shmem.c
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1502,9 +1502,8 @@ static struct page *shmem_alloc_page(gfp_t gfp,
 	return page;
 }
 
-static struct page *shmem_alloc_and_acct_page(gfp_t gfp,
-		struct inode *inode,
-		pgoff_t index, bool huge)
+static struct page *shmem_alloc_and_acct_page(gfp_t gfp, struct inode *inode,
+		pgoff_t index, bool fault, bool huge)
 {
 	struct shmem_inode_info *info = SHMEM_I(inode);
 	struct page *page;
@@ -1518,9 +1517,11 @@ static struct page *shmem_alloc_and_acct_page(gfp_t gfp,
 	if (!shmem_inode_acct_block(inode, nr))
 		goto failed;
 
-	if (huge)
+	if (huge) {
 		page = shmem_alloc_hugepage(gfp, info, index);
-	else
+		if (!page && fault)
+			count_vm_event(THP_FAULT_FALLBACK);
+	} else
 		page = shmem_alloc_page(gfp, info, index);
 	if (page) {
 		__SetPageLocked(page);
@@ -1832,11 +1833,10 @@ static int shmem_getpage_gfp(struct inode *inode, pgoff_t index,
 	}
 
 alloc_huge:
-	page = shmem_alloc_and_acct_page(gfp, inode, index, true);
+	page = shmem_alloc_and_acct_page(gfp, inode, index, vmf, true);
 	if (IS_ERR(page)) {
 alloc_nohuge:
-		page = shmem_alloc_and_acct_page(gfp, inode,
-						 index, false);
+		page = shmem_alloc_and_acct_page(gfp, inode, index, vmf, false);
 	}
 	if (IS_ERR(page)) {
 		int retry = 5;
@@ -1871,8 +1871,11 @@ static int shmem_getpage_gfp(struct inode *inode, pgoff_t index,
 
 	error = mem_cgroup_try_charge_delay(page, charge_mm, gfp, &memcg,
 					    PageTransHuge(page));
-	if (error)
+	if (error) {
+		if (vmf && PageTransHuge(page))
+			count_vm_event(THP_FAULT_FALLBACK);
 		goto unacct;
+	}
 	error = shmem_add_to_page_cache(page, mapping, hindex,
 					NULL, gfp & GFP_RECLAIM_MASK);
 	if (error) {
@@ -1883,6 +1886,8 @@ static int shmem_getpage_gfp(struct inode *inode, pgoff_t index,
 	mem_cgroup_commit_charge(page, memcg, false,
 				 PageTransHuge(page));
 	lru_cache_add_anon(page);
+	if (vmf && PageTransHuge(page))
+		count_vm_event(THP_FAULT_ALLOC);
 
 	spin_lock_irq(&info->lock);
 	info->alloced += compound_nr(page);