[PATCH 04/14] readahead: thrashing recovery method: check unbalanced aging

[Fengguang Wu <wfg@mail.ustc.edu.cn>]

[-- Attachment #1: readahead-thrashing-recovery-method-check-unbalanced-aging.patch --]
[-- Type: text/plain, Size: 1177 bytes --]

Always check for unbalanced aging in thrashing_recovery_readahead(), and
account RA_EVENT_READAHEAD_MUTILATE/RA_EVENT_READAHEAD_THRASHING events.

Unbalanced zone/node aging can come from abnormal system loads, or
misconfigured NUMA policies.

Thrashings are rare events, hence the cost of probe_page() is not a concern.

Signed-off-by: Fengguang Wu <wfg@mail.ustc.edu.cn>
---
 mm/readahead.c |   11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

--- linux-2.6.21-rc3-mm2.orig/mm/readahead.c
+++ linux-2.6.21-rc3-mm2/mm/readahead.c
@@ -1546,14 +1546,11 @@ thrashing_recovery_readahead(struct addr
 				pgoff_t offset, unsigned long ra_max)
 {
 	unsigned long ra_size;
+	int unbalanced_aging = probe_page(mapping, offset - 1);
 
-#ifdef CONFIG_DEBUG_READAHEAD
-	if (probe_page(mapping, offset - 1))
-		ra_account(ra, RA_EVENT_READAHEAD_MUTILATE,
-						ra->readahead_index - offset);
-	ra_account(ra, RA_EVENT_READAHEAD_THRASHING,
-						ra->readahead_index - offset);
-#endif
+	ra_account(ra, unbalanced_aging ? RA_EVENT_READAHEAD_MUTILATE :
+					  RA_EVENT_READAHEAD_THRASHING,
+					  ra->readahead_index - offset);
 
 	if (offset < ra->ra_index) {
 		/*

--