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Date: Tue, 10 Aug 2021 22:41:34 -0700
From: Daeho Jeong <daeho43@...il.com>
To: Chao Yu <chao@...nel.org>
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 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.
> > 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?
Plus, I wanted to allocate the blocks in a chunk sized between
<1..num>. This is a little bit different from what I meant.
> > +
> > 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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