f2fs: add a sysfs entry to control max_victim_search

Previously during SSR and GC, the maximum number of retrials to find a victim
segment was hard-coded by MAX_VICTIM_SEARCH, 4096 by default.

This number makes an effect on IO locality, when SSR mode is activated, which
results in performance fluctuation on some low-end devices.

If max_victim_search = 4, the victim will be searched like below.
("D" represents a dirty segment, and "*" indicates a selected victim segment.)

 D1 D2 D3 D4 D5 D6 D7 D8 D9
[   *       ]
      [   *    ]
            [         * ]
	                [ ....]

This patch adds a sysfs entry to control the number dynamically through:
  /sys/fs/f2fs/$dev/max_victim_search

Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/fs/f2fs/gc.h b/fs/f2fs/gc.h
index 507056d..5d5eb60 100644
--- a/fs/f2fs/gc.h
+++ b/fs/f2fs/gc.h
@@ -20,7 +20,7 @@
 #define LIMIT_FREE_BLOCK	40 /* percentage over invalid + free space */
 
 /* Search max. number of dirty segments to select a victim segment */
-#define MAX_VICTIM_SEARCH 4096 /* covers 8GB */
+#define DEF_MAX_VICTIM_SEARCH 4096 /* covers 8GB */
 
 struct f2fs_gc_kthread {
 	struct task_struct *f2fs_gc_task;