f2fs: avoid unnecessary search while finding victim in gc
variable nsearched in get_victim_by_default() indicates the number of
dirty segments we already checked. There are 2 problems about the way
it updates:
1. When p.ofs_unit is greater than 1, the victim we find consists
of multiple segments, possibly more than 1 dirty segment.
But nsearched always increases by 1.
2. If segments have been found but not been chosen, nsearched won't
increase. So even we have checked all dirty segments, nsearched
may still less than p.max_search.
All these problems could cause unnecessary search after all dirty
segments have already been checked.
Signed-off-by: Fan li <fanofcode.li@samsung.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
index d57245d..645273c 100644
--- a/fs/f2fs/gc.c
+++ b/fs/f2fs/gc.c
@@ -245,6 +245,18 @@
return get_cb_cost(sbi, segno);
}
+static unsigned int count_bits(const unsigned long *addr,
+ unsigned int offset, unsigned int len)
+{
+ unsigned int end = offset + len, sum = 0;
+
+ while (offset < end) {
+ if (test_bit(offset++, addr))
+ ++sum;
+ }
+ return sum;
+}
+
/*
* This function is called from two paths.
* One is garbage collection and the other is SSR segment selection.
@@ -260,7 +272,7 @@
struct victim_sel_policy p;
unsigned int secno, max_cost;
unsigned int last_segment = MAIN_SEGS(sbi);
- int nsearched = 0;
+ unsigned int nsearched = 0;
mutex_lock(&dirty_i->seglist_lock);
@@ -295,26 +307,31 @@
}
p.offset = segno + p.ofs_unit;
- if (p.ofs_unit > 1)
+ if (p.ofs_unit > 1) {
p.offset -= segno % p.ofs_unit;
+ nsearched += count_bits(p.dirty_segmap,
+ p.offset - p.ofs_unit,
+ p.ofs_unit);
+ } else {
+ nsearched++;
+ }
+
secno = GET_SECNO(sbi, segno);
if (sec_usage_check(sbi, secno))
- continue;
+ goto next;
if (gc_type == BG_GC && test_bit(secno, dirty_i->victim_secmap))
- continue;
+ goto next;
cost = get_gc_cost(sbi, segno, &p);
if (p.min_cost > cost) {
p.min_segno = segno;
p.min_cost = cost;
- } else if (unlikely(cost == max_cost)) {
- continue;
}
-
- if (nsearched++ >= p.max_search) {
+next:
+ if (nsearched >= p.max_search) {
sbi->last_victim[p.gc_mode] = segno;
break;
}