[PATCH v5] f2fs: introduce fragment allocation mode mount option
From: Daeho Jeong
Date: Wed Sep 29 2021 - 14:12:14 EST
From: Daeho Jeong <daehojeong@xxxxxxxxxx>
Added two options into "mode=" mount option to make it possible for
developers to simulate filesystem fragmentation/after-GC situation
itself. The developers use these modes to understand filesystem
fragmentation/after-GC condition well, and eventually get some
insights to handle them better.
"fragment:segment": f2fs allocates a new segment in ramdom position.
With this, we can simulate the after-GC condition.
"fragment:block" : We can scatter block allocation with
"max_fragment_chunk" and "max_fragment_hole" sysfs
nodes. f2fs will allocate 1..<max_fragment_chunk>
blocks in a chunk and make a hole in the length of
1..<max_fragment_hole> by turns in a newly allocated
free segment. Plus, this mode implicitly enables
"fragment:segment" option for more randomness.
Signed-off-by: Daeho Jeong <daehojeong@xxxxxxxxxx>
---
v5: get back to original two modes.
v4: implicitly enabled "fragment:segment" option only in
"fragment:rand_block".
v3: divided "fragment:block" mode and fixed a race condition related to
making chunks.
v2: changed mode name and added sysfs nodes to control the fragmentation
pattern.
---
Documentation/ABI/testing/sysfs-fs-f2fs | 16 ++++++++++++++++
Documentation/filesystems/f2fs.rst | 18 ++++++++++++++++++
fs/f2fs/f2fs.h | 19 +++++++++++++++++--
fs/f2fs/gc.c | 5 ++++-
fs/f2fs/segment.c | 20 ++++++++++++++++++--
fs/f2fs/segment.h | 1 +
fs/f2fs/super.c | 10 ++++++++++
fs/f2fs/sysfs.c | 20 ++++++++++++++++++++
8 files changed, 104 insertions(+), 5 deletions(-)
diff --git a/Documentation/ABI/testing/sysfs-fs-f2fs b/Documentation/ABI/testing/sysfs-fs-f2fs
index f627e705e663..b268e3e18b4a 100644
--- a/Documentation/ABI/testing/sysfs-fs-f2fs
+++ b/Documentation/ABI/testing/sysfs-fs-f2fs
@@ -512,3 +512,19 @@ Date: July 2021
Contact: "Daeho Jeong" <daehojeong@xxxxxxxxxx>
Description: You can control the multiplier value of bdi device readahead window size
between 2 (default) and 256 for POSIX_FADV_SEQUENTIAL advise option.
+
+What: /sys/fs/f2fs/<disk>/max_fragment_chunk
+Date: August 2021
+Contact: "Daeho Jeong" <daehojeong@xxxxxxxxxx>
+Description: With "mode=fragment:block" mount options, we can scatter block allocation.
+ f2fs will allocate 1..<max_fragment_chunk> blocks in a chunk and make a hole
+ in the length of 1..<max_fragment_hole> by turns. This value can be set
+ between 1..512 and the default value is 4.
+
+What: /sys/fs/f2fs/<disk>/max_fragment_hole
+Date: August 2021
+Contact: "Daeho Jeong" <daehojeong@xxxxxxxxxx>
+Description: With "mode=fragment:block" mount options, we can scatter block allocation.
+ f2fs will allocate 1..<max_fragment_chunk> blocks in a chunk and make a hole
+ in the length of 1..<max_fragment_hole> by turns. This value can be set
+ between 1..512 and the default value is 4.
diff --git a/Documentation/filesystems/f2fs.rst b/Documentation/filesystems/f2fs.rst
index 09de6ebbbdfa..4294db649fa8 100644
--- a/Documentation/filesystems/f2fs.rst
+++ b/Documentation/filesystems/f2fs.rst
@@ -201,6 +201,24 @@ fault_type=%d Support configuring fault injection type, should be
mode=%s Control block allocation mode which supports "adaptive"
and "lfs". In "lfs" mode, there should be no random
writes towards main area.
+ "fragment:segment" and "fragment:block" are newly added here.
+ These are developer options for experiments to simulate filesystem
+ fragmentation/after-GC situation itself. The developers use these
+ modes to understand filesystem fragmentation/after-GC condition well,
+ and eventually get some insights to handle them better.
+ In "fragment:segment", f2fs allocates a new segment in ramdom
+ position. With this, we can simulate the after-GC condition.
+ In "fragment:block", we can scatter block allocation with
+ "max_fragment_chunk" and "max_fragment_hole" sysfs nodes.
+ We added some randomness to both chunk and hole size to make
+ it close to realistic IO pattern. So, in this mode, f2fs will allocate
+ 1..<max_fragment_chunk> blocks in a chunk and make a hole in the
+ length of 1..<max_fragment_hole> by turns. With this, the newly
+ allocated blocks will be scattered throughout the whole partition.
+ Note that "fragment:block" implicitly enables "fragment:segment"
+ option for more randomness.
+ Please, use these options for your experiments and we strongly
+ recommend to re-format the filesystem after using these options.
io_bits=%u Set the bit size of write IO requests. It should be set
with "mode=lfs".
usrquota Enable plain user disk quota accounting.
diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index c24f03e054cb..6b574c3d426e 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -1285,8 +1285,10 @@ enum {
};
enum {
- FS_MODE_ADAPTIVE, /* use both lfs/ssr allocation */
- FS_MODE_LFS, /* use lfs allocation only */
+ FS_MODE_ADAPTIVE, /* use both lfs/ssr allocation */
+ FS_MODE_LFS, /* use lfs allocation only */
+ FS_MODE_FRAGMENT_SEG, /* segment fragmentation mode */
+ FS_MODE_FRAGMENT_BLK, /* block fragmentation mode */
};
enum {
@@ -1757,6 +1759,9 @@ struct f2fs_sb_info {
unsigned long seq_file_ra_mul; /* multiplier for ra_pages of seq. files in fadvise */
+ int max_fragment_chunk; /* max chunk size for block fragmentation mode */
+ int max_fragment_hole; /* max hole size for block fragmentation mode */
+
#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 */
@@ -3517,6 +3522,16 @@ 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 DEF_FRAGMENT_SIZE 4
+#define MIN_FRAGMENT_SIZE 1
+#define MAX_FRAGMENT_SIZE 512
+
+static inline bool f2fs_need_rand_seg(struct f2fs_sb_info *sbi)
+{
+ return F2FS_OPTION(sbi).fs_mode == FS_MODE_FRAGMENT_SEG ||
+ F2FS_OPTION(sbi).fs_mode == FS_MODE_FRAGMENT_BLK;
+}
+
/*
* checkpoint.c
*/
diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
index 2c18443972b6..72cfad99bbbe 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"
@@ -257,7 +258,9 @@ 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_rand_seg(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 a135d2247415..d648297a0132 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"
@@ -2630,6 +2631,8 @@ 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_rand_seg(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))
@@ -2681,6 +2684,9 @@ static void new_curseg(struct f2fs_sb_info *sbi, int type, bool new_sec)
curseg->next_segno = segno;
reset_curseg(sbi, type, 1);
curseg->alloc_type = LFS;
+ if (F2FS_OPTION(sbi).fs_mode == FS_MODE_FRAGMENT_BLK)
+ curseg->fragment_remained_chunk =
+ prandom_u32() % sbi->max_fragment_chunk + 1;
}
static int __next_free_blkoff(struct f2fs_sb_info *sbi,
@@ -2707,12 +2713,22 @@ static int __next_free_blkoff(struct f2fs_sb_info *sbi,
static void __refresh_next_blkoff(struct f2fs_sb_info *sbi,
struct curseg_info *seg)
{
- if (seg->alloc_type == SSR)
+ if (seg->alloc_type == SSR) {
seg->next_blkoff =
__next_free_blkoff(sbi, seg->segno,
seg->next_blkoff + 1);
- else
+ } else {
seg->next_blkoff++;
+ if (F2FS_OPTION(sbi).fs_mode == FS_MODE_FRAGMENT_BLK) {
+ /* To allocate block chunks in different sizes, use random number */
+ if (--seg->fragment_remained_chunk <= 0) {
+ seg->fragment_remained_chunk =
+ prandom_u32() % sbi->max_fragment_chunk + 1;
+ seg->next_blkoff +=
+ prandom_u32() % sbi->max_fragment_hole + 1;
+ }
+ }
+ }
}
bool f2fs_segment_has_free_slot(struct f2fs_sb_info *sbi, int segno)
diff --git a/fs/f2fs/segment.h b/fs/f2fs/segment.h
index 89fff258727d..46fde9f3f28e 100644
--- a/fs/f2fs/segment.h
+++ b/fs/f2fs/segment.h
@@ -314,6 +314,7 @@ struct curseg_info {
unsigned short next_blkoff; /* next block offset to write */
unsigned int zone; /* current zone number */
unsigned int next_segno; /* preallocated segment */
+ int fragment_remained_chunk; /* remained block size in a chunk for block fragmentation mode */
bool inited; /* indicate inmem log is inited */
};
diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
index 49e153fd8183..495a76e77927 100644
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -817,6 +817,10 @@ static int parse_options(struct super_block *sb, char *options, bool is_remount)
F2FS_OPTION(sbi).fs_mode = FS_MODE_ADAPTIVE;
} else if (!strcmp(name, "lfs")) {
F2FS_OPTION(sbi).fs_mode = FS_MODE_LFS;
+ } else if (!strcmp(name, "fragment:segment")) {
+ F2FS_OPTION(sbi).fs_mode = FS_MODE_FRAGMENT_SEG;
+ } else if (!strcmp(name, "fragment:block")) {
+ F2FS_OPTION(sbi).fs_mode = FS_MODE_FRAGMENT_BLK;
} else {
kfree(name);
return -EINVAL;
@@ -1897,6 +1901,10 @@ static int f2fs_show_options(struct seq_file *seq, struct dentry *root)
seq_puts(seq, "adaptive");
else if (F2FS_OPTION(sbi).fs_mode == FS_MODE_LFS)
seq_puts(seq, "lfs");
+ else if (F2FS_OPTION(sbi).fs_mode == FS_MODE_FRAGMENT_SEG)
+ seq_puts(seq, "fragment:segment");
+ else if (F2FS_OPTION(sbi).fs_mode == FS_MODE_FRAGMENT_BLK)
+ seq_puts(seq, "fragment:block");
seq_printf(seq, ",active_logs=%u", F2FS_OPTION(sbi).active_logs);
if (test_opt(sbi, RESERVE_ROOT))
seq_printf(seq, ",reserve_root=%u,resuid=%u,resgid=%u",
@@ -3515,6 +3523,8 @@ static void init_sb_info(struct f2fs_sb_info *sbi)
sbi->max_victim_search = DEF_MAX_VICTIM_SEARCH;
sbi->migration_granularity = sbi->segs_per_sec;
sbi->seq_file_ra_mul = MIN_RA_MUL;
+ sbi->max_fragment_chunk = DEF_FRAGMENT_SIZE;
+ sbi->max_fragment_hole = DEF_FRAGMENT_SIZE;
sbi->dir_level = DEF_DIR_LEVEL;
sbi->interval_time[CP_TIME] = DEF_CP_INTERVAL;
diff --git a/fs/f2fs/sysfs.c b/fs/f2fs/sysfs.c
index a1a3e0f6d658..54fc600a07b3 100644
--- a/fs/f2fs/sysfs.c
+++ b/fs/f2fs/sysfs.c
@@ -551,6 +551,22 @@ static ssize_t __sbi_store(struct f2fs_attr *a,
return count;
}
+ if (!strcmp(a->attr.name, "max_fragment_chunk")) {
+ if (t >= MIN_FRAGMENT_SIZE && t <= MAX_FRAGMENT_SIZE)
+ sbi->max_fragment_chunk = t;
+ else
+ return -EINVAL;
+ return count;
+ }
+
+ if (!strcmp(a->attr.name, "max_fragment_hole")) {
+ if (t >= MIN_FRAGMENT_SIZE && t <= MAX_FRAGMENT_SIZE)
+ sbi->max_fragment_hole = t;
+ else
+ return -EINVAL;
+ return count;
+ }
+
*ui = (unsigned int)t;
return count;
@@ -781,6 +797,8 @@ F2FS_RW_ATTR(ATGC_INFO, atgc_management, atgc_age_threshold, age_threshold);
F2FS_RW_ATTR(F2FS_SBI, f2fs_sb_info, seq_file_ra_mul, seq_file_ra_mul);
F2FS_RW_ATTR(F2FS_SBI, f2fs_sb_info, gc_segment_mode, gc_segment_mode);
F2FS_RW_ATTR(F2FS_SBI, f2fs_sb_info, gc_reclaimed_segments, gc_reclaimed_segs);
+F2FS_RW_ATTR(F2FS_SBI, f2fs_sb_info, max_fragment_chunk, max_fragment_chunk);
+F2FS_RW_ATTR(F2FS_SBI, f2fs_sb_info, max_fragment_hole, max_fragment_hole);
#define ATTR_LIST(name) (&f2fs_attr_##name.attr)
static struct attribute *f2fs_attrs[] = {
@@ -859,6 +877,8 @@ static struct attribute *f2fs_attrs[] = {
ATTR_LIST(seq_file_ra_mul),
ATTR_LIST(gc_segment_mode),
ATTR_LIST(gc_reclaimed_segments),
+ ATTR_LIST(max_fragment_chunk),
+ ATTR_LIST(max_fragment_hole),
NULL,
};
ATTRIBUTE_GROUPS(f2fs);
--
2.33.0.685.g46640cef36-goog