[PATCH 3/6] dax: add tracepoints to dax_load_hole()

[Ross Zwisler]

Add tracepoints to dax_load_hole(), following the same logging conventions
as the rest of DAX.

Here is the logging generated by a PTE read from a hole:

read-1075  [002] ....    62.362108: dax_pte_fault: dev 259:0 ino 0x1003
shared ALLOW_RETRY|KILLABLE|USER address 0x10480000 pgoff 0x280

read-1075  [002] ....    62.362140: dax_load_hole: dev 259:0 ino 0x1003
shared ALLOW_RETRY|KILLABLE|USER address 0x10480000 pgoff 0x280 NOPAGE

read-1075  [002] ....    62.362141: dax_pte_fault_done: dev 259:0 ino
0x1003 shared ALLOW_RETRY|KILLABLE|USER address 0x10480000 pgoff 0x280
NOPAGE

Signed-off-by: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
---
 fs/dax.c                      | 16 +++++++++++-----
 include/trace/events/fs_dax.h |  1 +
 2 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/fs/dax.c b/fs/dax.c
index b52732fb..bcfa11a 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -545,21 +545,25 @@ int dax_invalidate_mapping_entry_sync(struct address_space *mapping,
 static int dax_load_hole(struct address_space *mapping, void **entry,
 			 struct vm_fault *vmf)
 {
+	struct inode *inode = mapping->host;
 	struct page *page;
 	int ret;
 
 	/* Hole page already exists? Return it...  */
 	if (!radix_tree_exceptional_entry(*entry)) {
 		page = *entry;
-		goto out;
+		goto finish_fault;
 	}
 
 	/* This will replace locked radix tree entry with a hole page */
 	page = find_or_create_page(mapping, vmf->pgoff,
 				   vmf->gfp_mask | __GFP_ZERO);
-	if (!page)
-		return VM_FAULT_OOM;
- out:
+	if (!page) {
+		ret = VM_FAULT_OOM;
+		goto out;
+	}
+
+finish_fault:
 	vmf->page = page;
 	ret = finish_fault(vmf);
 	vmf->page = NULL;
@@ -567,8 +571,10 @@ static int dax_load_hole(struct address_space *mapping, void **entry,
 	if (!ret) {
 		/* Grab reference for PTE that is now referencing the page */
 		get_page(page);
-		return VM_FAULT_NOPAGE;
+		ret = VM_FAULT_NOPAGE;
 	}
+out:
+	trace_dax_load_hole(inode, vmf, ret);
 	return ret;
 }
 
diff --git a/include/trace/events/fs_dax.h b/include/trace/events/fs_dax.h
index b5a5209..2f15dfe 100644
--- a/include/trace/events/fs_dax.h
+++ b/include/trace/events/fs_dax.h
@@ -192,6 +192,7 @@ DEFINE_PTE_FAULT_EVENT(dax_pte_fault);
 DEFINE_PTE_FAULT_EVENT(dax_pte_fault_done);
 DEFINE_PTE_FAULT_EVENT(dax_pfn_mkwrite_no_entry);
 DEFINE_PTE_FAULT_EVENT(dax_pfn_mkwrite);
+DEFINE_PTE_FAULT_EVENT(dax_load_hole);
 
 #endif /* _TRACE_FS_DAX_H */
 
-- 
2.9.3