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Date: Wed, 11 Aug 2021 20:41:38 +0800
From: Chao Yu <chao@...nel.org>
To: Daeho Jeong <daeho43@...il.com>
Cc: linux-kernel@...r.kernel.org,
linux-f2fs-devel@...ts.sourceforge.net, kernel-team@...roid.com,
Daeho Jeong <daehojeong@...gle.com>
Subject: Re: [f2fs-dev] [PATCH v2] f2fs: introduce blk_alloc_mode mount option
On 2021/8/11 13:41, Daeho Jeong wrote:
> On Tue, Aug 10, 2021 at 6:58 PM Chao Yu <chao@...nel.org> wrote:
>>
>> On 2021/8/10 2:54, Daeho Jeong wrote:
>>> From: Daeho Jeong <daehojeong@...gle.com>
>>>
>>> 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
>>
>> At a glance, I think this functionality can be used to initialize filesystem
>> status as fragmented one, which is commonly used in the first step of aging
>> test, in order to make filesystem fragmented, aging program needs to fill
>> file or block sequentially and remove them at fixed interval, that takes a
>> lot of time. IMO, it will be great to support this by filesystem naturally
>> to save time of aging filessytem, rather just for experimental reasons to
>> understand filesystem behavior.
>>
>
> Yes, that's what I meant~ :)
>
>> Maybe we can add a new mode for filesystem allocation mode except adaptive
>> and lfs mode, maybe "fragment" mode... :P
>>
>
> Sounds good~ Could you suggest the names for both blk_random and seg_random.
> We need seg_random mode,too, in order to simulate after-GC condition.
mode=fragment:block and mode=fragment:segment?
>
>>> 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@...gle.com>
>>>
>>> ---
>>> 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;
>>> + }
>>> + }
>>
>> Why not adjusting __refresh_next_blkoff(), so we can control granularity of
>> allocation interval, e.g.
>>
>> if (seg->alloc_type == SSR)
>> seg->next_blkoff =
>> __next_free_blkoff(sbi, seg->segno,
>> seg->next_blkoff + 1);
>> else if (seg->alloc_type == LFS)
>> seg->next_blkoff++;
>> else
>> seg->next_blkoff += sbi->fragment_granularity;
>>
>> Thanks,
>>
>
> I am not sure this is safe, is this?
I didn't look into the details, but what I mean here is we can control
log header pointer directly to fragment filesystem as we expect.
> Plus, I wanted to allocate the blocks in a chunk sized between
> <1..num>. This is a little bit different from what I meant.
Ah, I see, maybe we can maintain an extra config cur_chunk_size for each
log header to control chunksize in fragmenting flow.
__refresh_next_blkoff()
seg->next_blkoff++;
seg->cur_chunk_size++;
if (seg->cur_chunk_size == sbi->fragment_chunk_size) {
seg->cur_chunk_size = 0;
seg->next_blkoff += sbi->fragment_hole_size;
}
.fragment_chunk_size + .fragment_hole_size should be 1 << n (1 <= n <= 9), e.g.:
a) data(4k) | hole(4k) | data | hole | ...
.fragment_chunk_size = 1
.fragment_hole_size = 1
b) data(12k) | hole(4k) | data | hole | ...
.fragment_chunk_size = 3
.fragment_hole_size = 1
c) data(4k) | hole (12k) |data | hole | ...
.fragment_chunk_size = 1
.fragment_hole_size = 3
And we can control .fragment_chunk_size and .fragment_hole_size via sysfs?
Thoughts?
Thanks,
>
>
>>> +
>>> 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;
>>>
>>>
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