[PATCH v2] f2fs: introduce blk_alloc_mode mount option
From: Daeho Jeong
Date: Mon Aug 09 2021 - 14:55:02 EST
From: Daeho Jeong <daehojeong@xxxxxxxxxx>
Added a mount option to control block allocation mode for filesystem
developer to simulate filesystem fragmentation and after-GC situation
for experimental reasons to understand the filesystem behaviors well
under the severe condition. This supports "normal", "seg_random" and
"blk_random:<num>" options.
"normal" (default): f2fs allocates blocks in the normal way.
"seg_random": f2fs allocates a new segment in ramdom position.
With this, we can simulate the after-GC condition.
"blk_random:<num>": We can make f2fs allocate only 1..<num> blocks
in a row and forcibly change the segment randomly.
With this, the newly allocated blocks will be scatter
throughout the whole partition and we can simulate
filesystem fragmentation condition.
Signed-off-by: Daeho Jeong <daehojeong@xxxxxxxxxx>
---
v2: changed the <num> initialization way.
---
Documentation/filesystems/f2fs.rst | 16 ++++++++++
fs/f2fs/f2fs.h | 20 +++++++++++++
fs/f2fs/gc.c | 5 +++-
fs/f2fs/segment.c | 12 ++++++++
fs/f2fs/super.c | 47 ++++++++++++++++++++++++++++++
5 files changed, 99 insertions(+), 1 deletion(-)
diff --git a/Documentation/filesystems/f2fs.rst b/Documentation/filesystems/f2fs.rst
index ff9e7cc97c65..a0ca963fda20 100644
--- a/Documentation/filesystems/f2fs.rst
+++ b/Documentation/filesystems/f2fs.rst
@@ -312,6 +312,22 @@ inlinecrypt When possible, encrypt/decrypt the contents of encrypted
Documentation/block/inline-encryption.rst.
atgc Enable age-threshold garbage collection, it provides high
effectiveness and efficiency on background GC.
+blk_alloc_mode=%s Control block allocation mode. This is a developer option
+ for experiments to simulate filesystem fragmentation and
+ after-GC situation. The developers use this mode to understand
+ filesystem fragmentation and after-GC condition well, and
+ eventually get the insight to handle them better.
+ This supports "normal", "seg_random" and "blk_random:<num>" modes.
+ In "normal" mode (default), f2fs allocates blocks in the normal way.
+ In "seg_random", f2fs allocates a new segment in ramdom position.
+ With this, we can simulate the after-GC condition.
+ In "blk_random:<num>", we can make f2fs allocate only 1..<num>
+ blocks in a row and forcibly change the segment randomly.
+ You can set the <num> within 1 .. 512 number.
+ With this, the newly allocated blocks will be scatter throughout
+ the whole partition and we can simulate filesystem fragmentation
+ condition. Please, use this option for your experiments and we
+ strongly recommand a filesystem format after using this option.
======================== ============================================================
Debugfs Entries
diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index fccee18ab776..aed09e8c0fce 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -155,6 +155,9 @@ struct f2fs_mount_info {
int compress_mode; /* compression mode */
unsigned char extensions[COMPRESS_EXT_NUM][F2FS_EXTENSION_LEN]; /* extensions */
unsigned char noextensions[COMPRESS_EXT_NUM][F2FS_EXTENSION_LEN]; /* extensions */
+
+ int blk_alloc_mode; /* block allocation mode */
+ int blk_alloc_random_max; /* the maximum chunk size for block random allocation mode */
};
#define F2FS_FEATURE_ENCRYPT 0x0001
@@ -1740,6 +1743,8 @@ struct f2fs_sb_info {
unsigned long seq_file_ra_mul; /* multiplier for ra_pages of seq. files in fadvise */
+ int blk_alloc_remained; /* remained block count for this block allocation period */
+
#ifdef CONFIG_F2FS_FS_COMPRESSION
struct kmem_cache *page_array_slab; /* page array entry */
unsigned int page_array_slab_size; /* default page array slab size */
@@ -3619,6 +3624,21 @@ unsigned int f2fs_usable_segs_in_sec(struct f2fs_sb_info *sbi,
unsigned int f2fs_usable_blks_in_seg(struct f2fs_sb_info *sbi,
unsigned int segno);
+#define MIN_BLK_ALLOC_RANDOM 1
+#define MAX_BLK_ALLOC_RANDOM 512
+
+enum {
+ BLK_ALLOC_MODE_NORMAL, /* normal block allocation mode */
+ BLK_ALLOC_MODE_SEG_RANDOM, /* make segment allocation random */
+ BLK_ALLOC_MODE_BLK_RANDOM, /* make block allocation random */
+};
+
+static inline bool f2fs_need_seg_random(struct f2fs_sb_info *sbi)
+{
+ return F2FS_OPTION(sbi).blk_alloc_mode == BLK_ALLOC_MODE_SEG_RANDOM ||
+ F2FS_OPTION(sbi).blk_alloc_mode == BLK_ALLOC_MODE_BLK_RANDOM;
+}
+
/*
* checkpoint.c
*/
diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
index 9dce44619069..571b50322e6e 100644
--- a/fs/f2fs/gc.c
+++ b/fs/f2fs/gc.c
@@ -14,6 +14,7 @@
#include <linux/delay.h>
#include <linux/freezer.h>
#include <linux/sched/signal.h>
+#include <linux/random.h>
#include "f2fs.h"
#include "node.h"
@@ -256,7 +257,9 @@ static void select_policy(struct f2fs_sb_info *sbi, int gc_type,
p->max_search = sbi->max_victim_search;
/* let's select beginning hot/small space first in no_heap mode*/
- if (test_opt(sbi, NOHEAP) &&
+ if (f2fs_need_seg_random(sbi))
+ p->offset = prandom_u32() % (MAIN_SECS(sbi) * sbi->segs_per_sec);
+ else if (test_opt(sbi, NOHEAP) &&
(type == CURSEG_HOT_DATA || IS_NODESEG(type)))
p->offset = 0;
else
diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index f9b7fb785e1d..6dff2d36ad6b 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -15,6 +15,7 @@
#include <linux/timer.h>
#include <linux/freezer.h>
#include <linux/sched/signal.h>
+#include <linux/random.h>
#include "f2fs.h"
#include "segment.h"
@@ -2587,6 +2588,8 @@ static unsigned int __get_next_segno(struct f2fs_sb_info *sbi, int type)
unsigned short seg_type = curseg->seg_type;
sanity_check_seg_type(sbi, seg_type);
+ if (f2fs_need_seg_random(sbi))
+ return prandom_u32() % (MAIN_SECS(sbi) * sbi->segs_per_sec);
/* if segs_per_sec is large than 1, we need to keep original policy. */
if (__is_large_section(sbi))
@@ -3150,6 +3153,15 @@ int f2fs_trim_fs(struct f2fs_sb_info *sbi, struct fstrim_range *range)
static bool __has_curseg_space(struct f2fs_sb_info *sbi,
struct curseg_info *curseg)
{
+ /* To allocate block chunks in different sizes, use random number */
+ if (F2FS_OPTION(sbi).blk_alloc_mode == BLK_ALLOC_MODE_BLK_RANDOM) {
+ if (--sbi->blk_alloc_remained < 0) {
+ sbi->blk_alloc_remained = prandom_u32() %
+ F2FS_OPTION(sbi).blk_alloc_random_max;
+ return false;
+ }
+ }
+
return curseg->next_blkoff < f2fs_usable_blks_in_seg(sbi,
curseg->segno);
}
diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
index 9ead6d2e703b..ef14f3e8b29a 100644
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -155,6 +155,7 @@ enum {
Opt_atgc,
Opt_gc_merge,
Opt_nogc_merge,
+ Opt_blk_alloc_mode,
Opt_err,
};
@@ -231,6 +232,7 @@ static match_table_t f2fs_tokens = {
{Opt_atgc, "atgc"},
{Opt_gc_merge, "gc_merge"},
{Opt_nogc_merge, "nogc_merge"},
+ {Opt_blk_alloc_mode, "blk_alloc_mode=%s"},
{Opt_err, NULL},
};
@@ -1173,6 +1175,40 @@ static int parse_options(struct super_block *sb, char *options, bool is_remount)
case Opt_nogc_merge:
clear_opt(sbi, GC_MERGE);
break;
+ case Opt_blk_alloc_mode:
+ name = match_strdup(&args[0]);
+ if (!name)
+ return -ENOMEM;
+ if (!strcmp(name, "normal")) {
+ F2FS_OPTION(sbi).blk_alloc_mode =
+ BLK_ALLOC_MODE_NORMAL;
+ } else if (!strcmp(name, "seg_random")) {
+ F2FS_OPTION(sbi).blk_alloc_mode =
+ BLK_ALLOC_MODE_SEG_RANDOM;
+ } else if (!strncmp(name, "blk_random:", 11)) {
+ const char *num = name + 11;
+ long size;
+
+ ret = kstrtol(num, 10, &size);
+ if (ret) {
+ kfree(name);
+ return ret;
+ }
+ if (size < MIN_BLK_ALLOC_RANDOM)
+ size = MIN_BLK_ALLOC_RANDOM;
+ else if (size > MAX_BLK_ALLOC_RANDOM)
+ size = MAX_BLK_ALLOC_RANDOM;
+
+ F2FS_OPTION(sbi).blk_alloc_mode =
+ BLK_ALLOC_MODE_BLK_RANDOM;
+ F2FS_OPTION(sbi).blk_alloc_random_max = size;
+ sbi->blk_alloc_remained = size;
+ } else {
+ kfree(name);
+ return -EINVAL;
+ }
+ kfree(name);
+ break;
default:
f2fs_err(sbi, "Unrecognized mount option \"%s\" or missing value",
p);
@@ -1919,6 +1955,14 @@ static int f2fs_show_options(struct seq_file *seq, struct dentry *root)
else if (F2FS_OPTION(sbi).fsync_mode == FSYNC_MODE_NOBARRIER)
seq_printf(seq, ",fsync_mode=%s", "nobarrier");
+ if (F2FS_OPTION(sbi).blk_alloc_mode == BLK_ALLOC_MODE_NORMAL)
+ seq_printf(seq, ",blk_alloc_mode=%s", "normal");
+ else if (F2FS_OPTION(sbi).blk_alloc_mode == BLK_ALLOC_MODE_SEG_RANDOM)
+ seq_printf(seq, ",blk_alloc_mode=%s", "seg_random");
+ else if (F2FS_OPTION(sbi).blk_alloc_mode == BLK_ALLOC_MODE_BLK_RANDOM)
+ seq_printf(seq, ",blk_alloc_mode=%s:%d", "blk_random",
+ F2FS_OPTION(sbi).blk_alloc_random_max);
+
#ifdef CONFIG_F2FS_FS_COMPRESSION
f2fs_show_compress_options(seq, sbi->sb);
#endif
@@ -1947,6 +1991,9 @@ static void default_options(struct f2fs_sb_info *sbi)
F2FS_OPTION(sbi).compress_ext_cnt = 0;
F2FS_OPTION(sbi).compress_mode = COMPR_MODE_FS;
F2FS_OPTION(sbi).bggc_mode = BGGC_MODE_ON;
+ F2FS_OPTION(sbi).blk_alloc_mode = BLK_ALLOC_MODE_NORMAL;
+ F2FS_OPTION(sbi).blk_alloc_random_max = MAX_BLK_ALLOC_RANDOM;
+ sbi->blk_alloc_remained = MAX_BLK_ALLOC_RANDOM;
sbi->sb->s_flags &= ~SB_INLINECRYPT;
--
2.32.0.605.g8dce9f2422-goog