Via https://lkml.org/lkml/2013/4/10/897, we can know that the relative design
idea is to keep
scan_target[anon] : scan_target[file]
== really_scanned_num[anon] : really_scanned_num[file]
But we can find the following snippet in shrink_lruvec():
if (nr_file > nr_anon) {
...
} else {
...
}
However, the above code fragment broke the design idea. We can assume:
nr[LRU_ACTIVE_FILE] = 30
nr[LRU_INACTIVE_FILE] = 30
nr[LRU_ACTIVE_ANON] = 0
nr[LRU_INACTIVE_ANON] = 40
When the value of (nr_reclaimed < nr_to_reclaim) become false, there are
the following results:
nr[LRU_ACTIVE_FILE] = 15
nr[LRU_INACTIVE_FILE] = 15
nr[LRU_ACTIVE_ANON] = 0
nr[LRU_INACTIVE_ANON] = 25
nr_file = 30
nr_anon = 25
file_percent = 30 / 60 = 0.5
anon_percent = 25 / 40 = 0.65
According to the above design idea, we should scan some pages from ANON,
but in fact we execute the an error code path due to "if (nr_file > nr_anon)".
In this way, nr[lru] is likely to be a negative number. Luckily,
"nr[lru] -= min(nr[lru], nr_scanned)" can help us to filter this situation,
but it has rebelled against our design idea.
Signed-off-by: Chen Yucong <sla...@gmail.com>
---
mm/vmscan.c | 39 ++++++++++++++++++---------------------
1 file changed, 18 insertions(+), 21 deletions(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index a8ffe4e..2c35e34 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2057,8 +2057,7 @@ out:
static void shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
{
unsigned long nr[NR_LRU_LISTS];
- unsigned long targets[NR_LRU_LISTS];
- unsigned long nr_to_scan;
+ unsigned long file_target, anon_target;
enum lru_list lru;
unsigned long nr_reclaimed = 0;
unsigned long nr_to_reclaim = sc->nr_to_reclaim;
@@ -2067,8 +2066,8 @@ static void shrink_lruvec(struct lruvec *lruvec, struct
scan_control *sc)
get_scan_count(lruvec, sc, nr);
- /* Record the original scan target for proportional adjustments later */
- memcpy(targets, nr, sizeof(nr));
+ file_target = nr[LRU_INACTIVE_FILE] + nr[LRU_ACTIVE_FILE];
+ anon_target = nr[LRU_INACTIVE_ANON] + nr[LRU_ACTIVE_ANON];
/*
* Global reclaiming within direct reclaim at DEF_PRIORITY is a normal
@@ -2087,8 +2086,8 @@ static void shrink_lruvec(struct lruvec *lruvec, struct
scan_control *sc)
blk_start_plug(&plug);
while (nr[LRU_INACTIVE_ANON] || nr[LRU_ACTIVE_FILE] ||
nr[LRU_INACTIVE_FILE]) {
- unsigned long nr_anon, nr_file, percentage;
- unsigned long nr_scanned;
+ unsigned long nr_anon, nr_file, file_percent, anon_percent;
+ unsigned long nr_to_scan, nr_scanned, percentage;
for_each_evictable_lru(lru) {
if (nr[lru]) {
@@ -2122,16 +2121,19 @@ static void shrink_lruvec(struct lruvec *lruvec, struct
scan_control *sc)
if (!nr_file || !nr_anon)
break;
- if (nr_file > nr_anon) {
- unsigned long scan_target = targets[LRU_INACTIVE_ANON] +
- targets[LRU_ACTIVE_ANON] + 1;
+ file_percent = nr_file * 100 / file_target;
+ anon_percent = nr_anon * 100 / anon_target;
+
+ if (file_percent > anon_percent) {
lru = LRU_BASE;
- percentage = nr_anon * 100 / scan_target;
+ nr_scanned = file_target - nr_file;
+ nr_to_scan = file_target * (100 - anon_percent) / 100;
+ percentage = nr[LRU_FILE] * 100 / nr_file;
} else {
- unsigned long scan_target = targets[LRU_INACTIVE_FILE] +
- targets[LRU_ACTIVE_FILE] + 1;
lru = LRU_FILE;
- percentage = nr_file * 100 / scan_target;
+ nr_scanned = anon_target - nr_anon;
+ nr_to_scan = anon_target * (100 - file_percent) / 100;
+ percentage = nr[LRU_BASE] * 100 / nr_anon;
}
/* Stop scanning the smaller of the LRU */
@@ -2143,14 +2145,9 @@ static void shrink_lruvec(struct lruvec *lruvec, struct
scan_control *sc)
* scan target and the percentage scanning already complete
*/
lru = (lru == LRU_FILE) ? LRU_BASE : LRU_FILE;
- nr_scanned = targets[lru] - nr[lru];
- nr[lru] = targets[lru] * (100 - percentage) / 100;
- nr[lru] -= min(nr[lru], nr_scanned);
-
- lru += LRU_ACTIVE;
- nr_scanned = targets[lru] - nr[lru];
- nr[lru] = targets[lru] * (100 - percentage) / 100;
- nr[lru] -= min(nr[lru], nr_scanned);
+ nr_to_scan -= min(nr_to_scan, nr_scanned);
+ nr[lru] = nr_to_scan * percentage / 100;
+ nr[lru + LRU_ACTIVE] = nr_to_scan - nr[lru];
scan_adjusted = true;
}
--
1.7.10.4
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