Re: [PATCH v4] f2fs: introduce fragment allocation mode mount option

From: Jaegeuk Kim
Date: Fri Sep 10 2021 - 19:13:15 EST

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On 09/02, Daeho Jeong wrote:
> From: Daeho Jeong <daehojeong@xxxxxxxxxx>
>
> Added three options into "mode=" mount option to make it possible for
> developers to make the filesystem fragmented or 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:fixed_block" : We can scatter block allocation with
> "fragment_chunk_size" and "fragment_hole_size" sysfs
> nodes. f2fs will allocate <fragment_chunk_size> blocks
> in a chunk and make a hole in the length of
> <fragment_hole_size> by turns in a newly allocated free
> segment.

Wait. Why do we need to add so many options here? I was expecting to see
performance difference when getting random segments or random blocks as
an extreme case. I don't get the point why we need the middle of those cases.

> "fragment:rand_block" : Working like "fragment:fixed_block" mode, but
> added some randomness to both chunk and hole size. So,
> f2fs will allocate 1..<fragment_chunk_size> blocks in a
> chunk and make a hole in the nodes. f2fs will allocate
> 1..<fragment_chunk_size> blocks in a chunk and make a
> hole in the length of 1..<fragment_hole_size> by turns
> in a newly allocated free segment.
> Plus, f2fs implicitly enables "fragment:segment" option
> for more randomness in allocation in "fragment:rand_block".
>
> Signed-off-by: Daeho Jeong <daehojeong@xxxxxxxxxx>
> ---
> 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 | 24 ++++++++++++++++++++
> Documentation/filesystems/f2fs.rst | 22 +++++++++++++++++++
> fs/f2fs/f2fs.h | 20 +++++++++++++++--
> fs/f2fs/gc.c | 5 ++++-
> fs/f2fs/segment.c | 29 +++++++++++++++++++++++--
> fs/f2fs/segment.h | 1 +
> fs/f2fs/super.c | 14 ++++++++++++
> fs/f2fs/sysfs.c | 20 +++++++++++++++++
> 8 files changed, 130 insertions(+), 5 deletions(-)
>
> diff --git a/Documentation/ABI/testing/sysfs-fs-f2fs b/Documentation/ABI/testing/sysfs-fs-f2fs
> index f627e705e663..d56ecfd16abf 100644
> --- a/Documentation/ABI/testing/sysfs-fs-f2fs
> +++ b/Documentation/ABI/testing/sysfs-fs-f2fs
> @@ -512,3 +512,27 @@ 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>/fragment_chunk_size
> +Date: August 2021
> +Contact: "Daeho Jeong" <daehojeong@xxxxxxxxxx>
> +Description: With "mode=fragment:fixed_block" and "mode=fragment:rand_block" mount options,
> + we can scatter block allocation. Using this node, in "fragment:fixed_block"
> + mode, f2fs will allocate <fragment_chunk_size> blocks in a chunk and make
> + a hole in the length of <fragment_hole_size> by turns in a newly allocated
> + free segment. Plus, in "fragment:rand_block" mode, f2fs will allocate
> + 1..<fragment_chunk_size> blocks in a chunk and make a hole in the length of
> + 1..<fragment_hole_size> by turns. This value can be set between 1..512 and
> + the default value is 4.
> +
> +What: /sys/fs/f2fs/<disk>/fragment_hole_size
> +Date: August 2021
> +Contact: "Daeho Jeong" <daehojeong@xxxxxxxxxx>
> +Description: With "mode=fragment:fixed_block" and "mode=fragment:rand_block" mount options,
> + we can scatter block allocation. Using this node, in "fragment:fixed_block"
> + mode, f2fs will allocate <fragment_chunk_size> blocks in a chunk and make
> + a hole in the length of <fragment_hole_size> by turns in a newly allocated
> + free segment. Plus, in "fragment:rand_block" mode, f2fs will allocate
> + 1..<fragment_chunk_size> blocks in a chunk and make a hole in the length of
> + 1..<fragment_hole_size> 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..04ddae8754cc 100644
> --- a/Documentation/filesystems/f2fs.rst
> +++ b/Documentation/filesystems/f2fs.rst
> @@ -201,6 +201,28 @@ 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", "fragment:fixed_block" and "fragment:rand_block"
> + are newly added here. These are developer options for experiments
> + to make the filesystem fragmented or 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:fixed_block" and "fragment:rand_block", we can scatter
> + block allocation with "fragment_chunk_size" and "fragment_hole_size"
> + sysfs nodes. In "fragment:fixed_block" mode, f2fs will allocate
> + <fragment_chunk_size> blocks in a chunk and make a hole in the length
> + of <fragment_hole_size> by turns in a newly allocated free segment.
> + But, in "fragment:rand_block" mode, f2fs adds some randomness to
> + both chunk and hole size. So, f2fs will allocate
> + 1..<fragment_chunk_size> blocks in a chunk and make a hole in the
> + length of 1..<fragment_hole_size> by turns. With these, the newly
> + allocated blocks will be scattered throughout the whole partition.
> + Plus, f2fs implicitly enables "fragment:segment" option for more
> + randomness in allocation in "fragment:rand_block".
> + 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..f9aa00b92222 100644
> --- a/fs/f2fs/f2fs.h
> +++ b/fs/f2fs/f2fs.h
> @@ -1285,8 +1285,11 @@ 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_FIXED_BLK, /* fixed block fragmentation mode */
> + FS_MODE_FRAGMENT_RAND_BLK, /* randomized block fragmentation mode */
> };
>
> enum {
> @@ -1757,6 +1760,9 @@ struct f2fs_sb_info {
>
> unsigned long seq_file_ra_mul; /* multiplier for ra_pages of seq. files in fadvise */
>
> + int fragment_chunk_size; /* the chunk size for block fragmentation mode */
> + int fragment_hole_size; /* the 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 +3523,16 @@ 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_RAND_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..954c06728b94 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 +2684,11 @@ 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_FIXED_BLK)
> + curseg->fragment_remained_chunk = sbi->fragment_chunk_size;
> + else if (F2FS_OPTION(sbi).fs_mode == FS_MODE_FRAGMENT_RAND_BLK)
> + curseg->fragment_remained_chunk =
> + prandom_u32() % sbi->fragment_chunk_size + 1;
> }
>
> static int __next_free_blkoff(struct f2fs_sb_info *sbi,
> @@ -2707,12 +2715,29 @@ 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_FIXED_BLK) {
> + if (--seg->fragment_remained_chunk <= 0) {
> + seg->fragment_remained_chunk =
> + sbi->fragment_chunk_size;
> + seg->next_blkoff +=
> + sbi->fragment_hole_size;
> + }
> + } else if (F2FS_OPTION(sbi).fs_mode == FS_MODE_FRAGMENT_RAND_BLK) {
> + /* To allocate block chunks in different sizes, use random number */
> + if (--seg->fragment_remained_chunk <= 0) {
> + seg->fragment_remained_chunk =
> + prandom_u32() % sbi->fragment_chunk_size + 1;
> + seg->next_blkoff +=
> + prandom_u32() % sbi->fragment_hole_size + 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..60067b6d9fea 100644
> --- a/fs/f2fs/super.c
> +++ b/fs/f2fs/super.c
> @@ -817,6 +817,12 @@ 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:fixed_block")) {
> + F2FS_OPTION(sbi).fs_mode = FS_MODE_FRAGMENT_FIXED_BLK;
> + } else if (!strcmp(name, "fragment:rand_block")) {
> + F2FS_OPTION(sbi).fs_mode = FS_MODE_FRAGMENT_RAND_BLK;
> } else {
> kfree(name);
> return -EINVAL;
> @@ -1897,6 +1903,12 @@ 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_FIXED_BLK)
> + seq_puts(seq, "fragment:fixed_block");
> + else if (F2FS_OPTION(sbi).fs_mode == FS_MODE_FRAGMENT_RAND_BLK)
> + seq_puts(seq, "fragment:rand_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 +3527,8 @@ 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->fragment_chunk_size = DEF_FRAGMENT_SIZE;
> + sbi->fragment_hole_size = 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..ab34b3c2e09d 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, "fragment_chunk_size")) {
> + if (t >= MIN_FRAGMENT_SIZE && t <= MAX_FRAGMENT_SIZE)
> + sbi->fragment_chunk_size = t;
> + else
> + return -EINVAL;
> + return count;
> + }
> +
> + if (!strcmp(a->attr.name, "fragment_hole_size")) {
> + if (t >= MIN_FRAGMENT_SIZE && t <= MAX_FRAGMENT_SIZE)
> + sbi->fragment_hole_size = 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, fragment_chunk_size, fragment_chunk_size);
> +F2FS_RW_ATTR(F2FS_SBI, f2fs_sb_info, fragment_hole_size, fragment_hole_size);
>
> #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(fragment_chunk_size),
> + ATTR_LIST(fragment_hole_size),
> NULL,
> };
> ATTRIBUTE_GROUPS(f2fs);
> --
> 2.33.0.153.gba50c8fa24-goog

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