Hi,
The fault accounting of filemap_dopage() is currently unable to account
for readahead pages as major faults.
Which means that getrusage's major fault reporting is pretty useless.
Fix that by using the PageReferenced and PageActive bits: allows
differentiation between newly accessed pages and reaccessed pages.
Follows the output of "/usr/bin/time -v" of an app which reads
10MB through a mapping on cold pagecache.
BEFORE PATCH:
Size: 10MB
Loops: 10
opening ./scan-testfile
reading scan-testfile, length = 10MB
Command being timed: "./scan-shared 10 10"
<snip>
Major (requiring I/O) page faults: 225
Minor (reclaiming a frame) page faults: 2437
AFTER PATCH:
Size: 10MB
Loops: 10
opening ./scan-testfile
reading scan-testfile, length = 10MB
Command being timed: "./scan-shared 10 10"
<>snip>
Major (requiring I/O) page faults: 2562
Minor (reclaiming a frame) page faults: 101
Signed-off-by: Marcelo Tosatti <[email protected]>
diff --git a/mm/filemap.c b/mm/filemap.c
index 5d6e4c2..8655443 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1237,14 +1237,6 @@ retry_find:
if (ra->mmap_miss > ra->mmap_hit + MMAP_LOTSAMISS)
goto no_cached_page;
- /*
- * To keep the pgmajfault counter straight, we need to
- * check did_readaround, as this is an inner loop.
- */
- if (!did_readaround) {
- majmin = VM_FAULT_MAJOR;
- inc_page_state(pgmajfault);
- }
did_readaround = 1;
ra_pages = max_sane_readahead(file->f_ra.ra_pages);
if (ra_pages) {
@@ -1273,6 +1265,15 @@ success:
/*
* Found the page and have a reference on it.
*/
+ if (PageActive(page) && !PageReferenced(page)) {
+ /* only account active pages as major faults, since inactive
+ * pages might have their referenced bit cleaned by
+ * memory scanning.
+ */
+ majmin = VM_FAULT_MAJOR;
+ inc_page_state(pgmajfault);
+ }
+
mark_page_accessed(page);
if (type)
*type = majmin;
@@ -1312,10 +1313,6 @@ no_cached_page:
return NULL;
page_not_uptodate:
- if (!did_readaround) {
- majmin = VM_FAULT_MAJOR;
- inc_page_state(pgmajfault);
- }
lock_page(page);
/* Did it get unhashed while we waited for it? */
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Stuff]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
[Linux Resources]
