f2fs: introduce sysfs entry to control in-place-update policy

This patch introduces new sysfs entries for users to control the policy of
in-place-updates, namely IPU, in f2fs.

Sometimes f2fs suffers from performance degradation due to its out-of-place
update policy that produces many additional node block writes.
If the storage performance is very dependant on the amount of data writes
instead of IO patterns, we'd better drop this out-of-place update policy.

This patch suggests 5 polcies and their triggering conditions as follows.

[sysfs entry name = ipu_policy]

0: F2FS_IPU_FORCE       all the time,
1: F2FS_IPU_SSR         if SSR mode is activated,
2: F2FS_IPU_UTIL        if FS utilization is over threashold,
3: F2FS_IPU_SSR_UTIL    if SSR mode is activated and FS utilization is over
                        threashold,
4: F2FS_IPU_DISABLE    disable IPU. (=default option)

[sysfs entry name = min_ipu_util]

This parameter controls the threshold to trigger in-place-updates.
The number indicates percentage of the filesystem utilization, and used by
F2FS_IPU_UTIL and F2FS_IPU_SSR_UTIL policies.

For more details, see need_inplace_update() in segment.h.
Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>

Documentation/filesystems/f2fs.txt

@@ -171,6 +171,17 @@ Files in /sys/fs/f2fs/<devname>
 			      conduct checkpoint to reclaim the prefree segments
 			      to free segments. By default, 100 segments, 200MB.
 
+ ipu_policy                   This parameter controls the policy of in-place
+                              updates in f2fs. There are five policies:
+                               0: F2FS_IPU_FORCE, 1: F2FS_IPU_SSR,
+                               2: F2FS_IPU_UTIL,  3: F2FS_IPU_SSR_UTIL,
+                               4: F2FS_IPU_DISABLE.
+
+ min_ipu_util                 This parameter controls the threshold to trigger
+                              in-place-updates. The number indicates percentage
+                              of the filesystem utilization, and used by
+                              F2FS_IPU_UTIL and F2FS_IPU_SSR_UTIL policies.
+
 ================================================================================
 USAGE
 ================================================================================

fs/f2fs/f2fs.h

@@ -325,6 +325,9 @@ struct f2fs_sm_info {
 	struct list_head discard_list;		/* 4KB discard list */
 	int nr_discards;			/* # of discards in the list */
 	int max_discards;			/* max. discards to be issued */
+
+	unsigned int ipu_policy;	/* in-place-update policy */
+	unsigned int min_ipu_util;	/* in-place-update threshold */
 };
 
 /*

fs/f2fs/segment.c

@@ -1799,6 +1799,8 @@ int build_segment_manager(struct f2fs_sb_info *sbi)
 	sm_info->main_segments = le32_to_cpu(raw_super->segment_count_main);
 	sm_info->ssa_blkaddr = le32_to_cpu(raw_super->ssa_blkaddr);
 	sm_info->rec_prefree_segments = DEF_RECLAIM_PREFREE_SEGMENTS;
+	sm_info->ipu_policy = F2FS_IPU_DISABLE;
+	sm_info->min_ipu_util = DEF_MIN_IPU_UTIL;
 
 	INIT_LIST_HEAD(&sm_info->discard_list);
 	sm_info->nr_discards = 0;

fs/f2fs/segment.h

@@ -476,19 +476,51 @@ static inline int utilization(struct f2fs_sb_info *sbi)
 
 /*
  * Sometimes f2fs may be better to drop out-of-place update policy.
- * So, if fs utilization is over MIN_IPU_UTIL, then f2fs tries to write
- * data in the original place likewise other traditional file systems.
- * But, currently set 100 in percentage, which means it is disabled.
- * See below need_inplace_update().
+ * And, users can control the policy through sysfs entries.
+ * There are five policies with triggering conditions as follows.
+ * F2FS_IPU_FORCE - all the time,
+ * F2FS_IPU_SSR - if SSR mode is activated,
+ * F2FS_IPU_UTIL - if FS utilization is over threashold,
+ * F2FS_IPU_SSR_UTIL - if SSR mode is activated and FS utilization is over
+ *                     threashold,
+ * F2FS_IPUT_DISABLE - disable IPU. (=default option)
  */
-#define MIN_IPU_UTIL		100
+#define DEF_MIN_IPU_UTIL	70
+
+enum {
+	F2FS_IPU_FORCE,
+	F2FS_IPU_SSR,
+	F2FS_IPU_UTIL,
+	F2FS_IPU_SSR_UTIL,
+	F2FS_IPU_DISABLE,
+};
+
 static inline bool need_inplace_update(struct inode *inode)
 {
 	struct f2fs_sb_info *sbi = F2FS_SB(inode->i_sb);
+
+	/* IPU can be done only for the user data */
 	if (S_ISDIR(inode->i_mode))
 		return false;
-	if (need_SSR(sbi) && utilization(sbi) > MIN_IPU_UTIL)
+
+	switch (SM_I(sbi)->ipu_policy) {
+	case F2FS_IPU_FORCE:
+		return true;
+	case F2FS_IPU_SSR:
+		if (need_SSR(sbi))
+			return true;
+		break;
+	case F2FS_IPU_UTIL:
+		if (utilization(sbi) > SM_I(sbi)->min_ipu_util)
 			return true;
+		break;
+	case F2FS_IPU_SSR_UTIL:
+		if (need_SSR(sbi) && utilization(sbi) > SM_I(sbi)->min_ipu_util)
+			return true;
+		break;
+	case F2FS_IPU_DISABLE:
+		break;
+	}
 	return false;
 }
 

fs/f2fs/super.c

@@ -178,6 +178,8 @@ F2FS_RW_ATTR(GC_THREAD, f2fs_gc_kthread, gc_no_gc_sleep_time, no_gc_sleep_time);
 F2FS_RW_ATTR(GC_THREAD, f2fs_gc_kthread, gc_idle, gc_idle);
 F2FS_RW_ATTR(SM_INFO, f2fs_sm_info, reclaim_segments, rec_prefree_segments);
 F2FS_RW_ATTR(SM_INFO, f2fs_sm_info, max_small_discards, max_discards);
+F2FS_RW_ATTR(SM_INFO, f2fs_sm_info, ipu_policy, ipu_policy);
+F2FS_RW_ATTR(SM_INFO, f2fs_sm_info, min_ipu_util, min_ipu_util);
 
 #define ATTR_LIST(name) (&f2fs_attr_##name.attr)
 static struct attribute *f2fs_attrs[] = {
@@ -187,6 +189,8 @@ static struct attribute *f2fs_attrs[] = {
 	ATTR_LIST(gc_idle),
 	ATTR_LIST(reclaim_segments),
 	ATTR_LIST(max_small_discards),
+	ATTR_LIST(ipu_policy),
+	ATTR_LIST(min_ipu_util),
 	NULL,
 };