[PATCH 1/1] mm: vmstat: introducing vm counter for slowpath

[Pintu Kumar <pintu.k@samsung.com>]

This patch add new counter slowpath_entered in /proc/vmstat to
track how many times the system entered into slowpath after
first allocation attempt is failed.
This is useful to know the rate of allocation success within
the slowpath.
This patch is tested on ARM with 512MB RAM.
A sample output is shown below after successful boot-up:
shell> cat /proc/vmstat
nr_free_pages 4712
pgalloc_normal 1319432
pgalloc_movable 0
pageoutrun 379
allocstall 0
slowpath_entered 585
compact_stall 0
compact_fail 0
compact_success 0

>From the above output we can see that the system entered
slowpath 585 times.
But the existing counter kswapd(pageoutrun), direct_reclaim(allocstall),
direct_compact(compact_stall) does not tell this value.
>From the above value, it clearly indicates that the system have
entered slowpath 585 times. Out of which 379 times allocation passed
through kswapd, without performing direct reclaim/compaction.
That means the remaining 206 times the allocation would have succeeded
using the alloc_pages_high_priority.

Signed-off-by: Pintu Kumar <pintu.k@samsung.com>
---
 include/linux/vm_event_item.h |    2 +-
 mm/page_alloc.c               |    2 ++
 mm/vmstat.c                   |    2 +-
 3 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/include/linux/vm_event_item.h b/include/linux/vm_event_item.h
index 2b1cef8..9825f294 100644
--- a/include/linux/vm_event_item.h
+++ b/include/linux/vm_event_item.h
@@ -37,7 +37,7 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
 #endif
 		PGINODESTEAL, SLABS_SCANNED, KSWAPD_INODESTEAL,
 		KSWAPD_LOW_WMARK_HIT_QUICKLY, KSWAPD_HIGH_WMARK_HIT_QUICKLY,
-		PAGEOUTRUN, ALLOCSTALL, PGROTATED,
+		PAGEOUTRUN, ALLOCSTALL, SLOWPATH_ENTERED, PGROTATED,
 		DROP_PAGECACHE, DROP_SLAB,
 #ifdef CONFIG_NUMA_BALANCING
 		NUMA_PTE_UPDATES,
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 2024d2e..4a5d487 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3029,6 +3029,8 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
 	if (IS_ENABLED(CONFIG_NUMA) && (gfp_mask & __GFP_THISNODE) && !wait)
 		goto nopage;
 
+	count_vm_event(SLOWPATH_ENTERED);
+
 retry:
 	if (!(gfp_mask & __GFP_NO_KSWAPD))
 		wake_all_kswapds(order, ac);
diff --git a/mm/vmstat.c b/mm/vmstat.c
index 1fd0886..1c54fdf 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -778,7 +778,7 @@ const char * const vmstat_text[] = {
 	"kswapd_high_wmark_hit_quickly",
 	"pageoutrun",
 	"allocstall",
-
+	"slowpath_entered",
 	"pgrotated",
 
 	"drop_pagecache",
-- 
1.7.9.5

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