[patch 109/114] dax: add tracepoints to dax_load_hole()

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From: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
Subject: dax: add tracepoints to dax_load_hole()

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

Link: http://lkml.kernel.org/r/20170221195116.13278-4-ross.zwisler@xxxxxxxxxxxxxxx
Signed-off-by: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
Reviewed-by: Jan Kara <jack@xxxxxxx>
Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Matthew Wilcox <mawilcox@xxxxxxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 fs/dax.c                      |   16 +++++++++++-----
 include/trace/events/fs_dax.h |    1 +
 2 files changed, 12 insertions(+), 5 deletions(-)

diff -puN fs/dax.c~dax-add-tracepoints-to-dax_load_hole fs/dax.c
--- a/fs/dax.c~dax-add-tracepoints-to-dax_load_hole
+++ a/fs/dax.c
@@ -509,21 +509,25 @@ int dax_invalidate_mapping_entry_sync(st
 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;
@@ -531,8 +535,10 @@ static int dax_load_hole(struct address_
 	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 -puN include/trace/events/fs_dax.h~dax-add-tracepoints-to-dax_load_hole include/trace/events/fs_dax.h
--- a/include/trace/events/fs_dax.h~dax-add-tracepoints-to-dax_load_hole
+++ a/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 */
 
_
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