Re: [PATCH] f2fs: introduce gc_merge mount option
From: Gao Xiang
Date: Sat Mar 27 2021 - 06:14:28 EST
On Sat, Mar 27, 2021 at 05:57:06PM +0800, Chao Yu wrote:
> In this patch, we will add two new mount options: "gc_merge" and
> "nogc_merge", when background_gc is on, "gc_merge" option can be
> set to let background GC thread to handle foreground GC requests,
> it can eliminate the sluggish issue caused by slow foreground GC
> operation when GC is triggered from a process with limited I/O
> and CPU resources.
>
> Original idea is from Xiang.
>
> Signed-off-by: Gao Xiang <xiang@xxxxxxxxxx>
> Signed-off-by: Chao Yu <yuchao0@xxxxxxxxxx>
Ah, that was a quite old commit many years ago due to priority inversion
issue ;-) I vaguely remembered some potential wakeup race condition which
was addressed in the internal branch...Yet I have no idea about those now
LOL.
Thanks for redoing this and sending it out to the upstream... :-)
Thanks,
Gao Xiang
> ---
> Documentation/filesystems/f2fs.rst | 6 ++++++
> fs/f2fs/f2fs.h | 1 +
> fs/f2fs/gc.c | 26 ++++++++++++++++++++++----
> fs/f2fs/gc.h | 6 ++++++
> fs/f2fs/segment.c | 15 +++++++++++++--
> fs/f2fs/super.c | 19 +++++++++++++++++--
> 6 files changed, 65 insertions(+), 8 deletions(-)
>
> diff --git a/Documentation/filesystems/f2fs.rst b/Documentation/filesystems/f2fs.rst
> index 35ed01a5fbc9..63c0c49b726d 100644
> --- a/Documentation/filesystems/f2fs.rst
> +++ b/Documentation/filesystems/f2fs.rst
> @@ -110,6 +110,12 @@ background_gc=%s Turn on/off cleaning operations, namely garbage
> on synchronous garbage collection running in background.
> Default value for this option is on. So garbage
> collection is on by default.
> +gc_merge When background_gc is on, this option can be enabled to
> + let background GC thread to handle foreground GC requests,
> + it can eliminate the sluggish issue caused by slow foreground
> + GC operation when GC is triggered from a process with limited
> + I/O and CPU resources.
> +nogc_merge Disable GC merge feature.
> disable_roll_forward Disable the roll-forward recovery routine
> norecovery Disable the roll-forward recovery routine, mounted read-
> only (i.e., -o ro,disable_roll_forward)
> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> index fe380bcf8d4d..87d734f5589d 100644
> --- a/fs/f2fs/f2fs.h
> +++ b/fs/f2fs/f2fs.h
> @@ -97,6 +97,7 @@ extern const char *f2fs_fault_name[FAULT_MAX];
> #define F2FS_MOUNT_NORECOVERY 0x04000000
> #define F2FS_MOUNT_ATGC 0x08000000
> #define F2FS_MOUNT_MERGE_CHECKPOINT 0x10000000
> +#define F2FS_MOUNT_GC_MERGE 0x20000000
>
> #define F2FS_OPTION(sbi) ((sbi)->mount_opt)
> #define clear_opt(sbi, option) (F2FS_OPTION(sbi).opt &= ~F2FS_MOUNT_##option)
> diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
> index a2ca483f9855..5c48825fd12d 100644
> --- a/fs/f2fs/gc.c
> +++ b/fs/f2fs/gc.c
> @@ -31,19 +31,24 @@ static int gc_thread_func(void *data)
> struct f2fs_sb_info *sbi = data;
> struct f2fs_gc_kthread *gc_th = sbi->gc_thread;
> wait_queue_head_t *wq = &sbi->gc_thread->gc_wait_queue_head;
> + wait_queue_head_t *fggc_wq = &sbi->gc_thread->fggc_wq;
> unsigned int wait_ms;
>
> wait_ms = gc_th->min_sleep_time;
>
> set_freezable();
> do {
> - bool sync_mode;
> + bool sync_mode, foreground = false;
>
> wait_event_interruptible_timeout(*wq,
> kthread_should_stop() || freezing(current) ||
> + waitqueue_active(fggc_wq) ||
> gc_th->gc_wake,
> msecs_to_jiffies(wait_ms));
>
> + if (test_opt(sbi, GC_MERGE) && waitqueue_active(fggc_wq))
> + foreground = true;
> +
> /* give it a try one time */
> if (gc_th->gc_wake)
> gc_th->gc_wake = 0;
> @@ -90,7 +95,10 @@ static int gc_thread_func(void *data)
> goto do_gc;
> }
>
> - if (!down_write_trylock(&sbi->gc_lock)) {
> + if (foreground) {
> + down_write(&sbi->gc_lock);
> + goto do_gc;
> + } else if (!down_write_trylock(&sbi->gc_lock)) {
> stat_other_skip_bggc_count(sbi);
> goto next;
> }
> @@ -107,14 +115,22 @@ static int gc_thread_func(void *data)
> else
> increase_sleep_time(gc_th, &wait_ms);
> do_gc:
> - stat_inc_bggc_count(sbi->stat_info);
> + if (!foreground)
> + stat_inc_bggc_count(sbi->stat_info);
>
> sync_mode = F2FS_OPTION(sbi).bggc_mode == BGGC_MODE_SYNC;
>
> + /* foreground GC was been triggered via f2fs_balance_fs() */
> + if (foreground)
> + sync_mode = false;
> +
> /* if return value is not zero, no victim was selected */
> - if (f2fs_gc(sbi, sync_mode, true, false, NULL_SEGNO))
> + if (f2fs_gc(sbi, sync_mode, !foreground, false, NULL_SEGNO))
> wait_ms = gc_th->no_gc_sleep_time;
>
> + if (foreground)
> + wake_up_all(&gc_th->fggc_wq);
> +
> trace_f2fs_background_gc(sbi->sb, wait_ms,
> prefree_segments(sbi), free_segments(sbi));
>
> @@ -148,6 +164,7 @@ int f2fs_start_gc_thread(struct f2fs_sb_info *sbi)
>
> sbi->gc_thread = gc_th;
> init_waitqueue_head(&sbi->gc_thread->gc_wait_queue_head);
> + init_waitqueue_head(&sbi->gc_thread->fggc_wq);
> sbi->gc_thread->f2fs_gc_task = kthread_run(gc_thread_func, sbi,
> "f2fs_gc-%u:%u", MAJOR(dev), MINOR(dev));
> if (IS_ERR(gc_th->f2fs_gc_task)) {
> @@ -165,6 +182,7 @@ void f2fs_stop_gc_thread(struct f2fs_sb_info *sbi)
> if (!gc_th)
> return;
> kthread_stop(gc_th->f2fs_gc_task);
> + wake_up_all(&gc_th->fggc_wq);
> kfree(gc_th);
> sbi->gc_thread = NULL;
> }
> diff --git a/fs/f2fs/gc.h b/fs/f2fs/gc.h
> index 0c8dae12dc51..3fe145e8e594 100644
> --- a/fs/f2fs/gc.h
> +++ b/fs/f2fs/gc.h
> @@ -42,6 +42,12 @@ struct f2fs_gc_kthread {
>
> /* for changing gc mode */
> unsigned int gc_wake;
> +
> + /* for GC_MERGE mount option */
> + wait_queue_head_t fggc_wq; /*
> + * caller of f2fs_balance_fs()
> + * will wait on this wait queue.
> + */
> };
>
> struct gc_inode_list {
> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> index 24ad45f5e335..31ccea1378fa 100644
> --- a/fs/f2fs/segment.c
> +++ b/fs/f2fs/segment.c
> @@ -503,8 +503,19 @@ void f2fs_balance_fs(struct f2fs_sb_info *sbi, bool need)
> * dir/node pages without enough free segments.
> */
> if (has_not_enough_free_secs(sbi, 0, 0)) {
> - down_write(&sbi->gc_lock);
> - f2fs_gc(sbi, false, false, false, NULL_SEGNO);
> + if (test_opt(sbi, GC_MERGE) && sbi->gc_thread &&
> + sbi->gc_thread->f2fs_gc_task) {
> + DEFINE_WAIT(wait);
> +
> + prepare_to_wait(&sbi->gc_thread->fggc_wq, &wait,
> + TASK_UNINTERRUPTIBLE);
> + wake_up(&sbi->gc_thread->gc_wait_queue_head);
> + io_schedule();
> + finish_wait(&sbi->gc_thread->fggc_wq, &wait);
> + } else {
> + down_write(&sbi->gc_lock);
> + f2fs_gc(sbi, false, false, false, NULL_SEGNO);
> + }
> }
> }
>
> diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
> index b48281642e98..954b1fe97d67 100644
> --- a/fs/f2fs/super.c
> +++ b/fs/f2fs/super.c
> @@ -151,6 +151,8 @@ enum {
> Opt_compress_chksum,
> Opt_compress_mode,
> Opt_atgc,
> + Opt_gc_merge,
> + Opt_nogc_merge,
> Opt_err,
> };
>
> @@ -223,6 +225,8 @@ static match_table_t f2fs_tokens = {
> {Opt_compress_chksum, "compress_chksum"},
> {Opt_compress_mode, "compress_mode=%s"},
> {Opt_atgc, "atgc"},
> + {Opt_gc_merge, "gc_merge"},
> + {Opt_nogc_merge, "nogc_merge"},
> {Opt_err, NULL},
> };
>
> @@ -1073,6 +1077,12 @@ static int parse_options(struct super_block *sb, char *options, bool is_remount)
> case Opt_atgc:
> set_opt(sbi, ATGC);
> break;
> + case Opt_gc_merge:
> + set_opt(sbi, GC_MERGE);
> + break;
> + case Opt_nogc_merge:
> + clear_opt(sbi, GC_MERGE);
> + break;
> default:
> f2fs_err(sbi, "Unrecognized mount option \"%s\" or missing value",
> p);
> @@ -1675,6 +1685,9 @@ static int f2fs_show_options(struct seq_file *seq, struct dentry *root)
> else if (F2FS_OPTION(sbi).bggc_mode == BGGC_MODE_OFF)
> seq_printf(seq, ",background_gc=%s", "off");
>
> + if (test_opt(sbi, GC_MERGE))
> + seq_puts(seq, ",gc_merge");
> +
> if (test_opt(sbi, DISABLE_ROLL_FORWARD))
> seq_puts(seq, ",disable_roll_forward");
> if (test_opt(sbi, NORECOVERY))
> @@ -2038,7 +2051,8 @@ static int f2fs_remount(struct super_block *sb, int *flags, char *data)
> * option. Also sync the filesystem.
> */
> if ((*flags & SB_RDONLY) ||
> - F2FS_OPTION(sbi).bggc_mode == BGGC_MODE_OFF) {
> + (F2FS_OPTION(sbi).bggc_mode == BGGC_MODE_OFF &&
> + !test_opt(sbi, GC_MERGE))) {
> if (sbi->gc_thread) {
> f2fs_stop_gc_thread(sbi);
> need_restart_gc = true;
> @@ -4012,7 +4026,8 @@ static int f2fs_fill_super(struct super_block *sb, void *data, int silent)
> * If filesystem is not mounted as read-only then
> * do start the gc_thread.
> */
> - if (F2FS_OPTION(sbi).bggc_mode != BGGC_MODE_OFF && !f2fs_readonly(sb)) {
> + if ((F2FS_OPTION(sbi).bggc_mode != BGGC_MODE_OFF ||
> + test_opt(sbi, GC_MERGE)) && !f2fs_readonly(sb)) {
> /* After POR, we can run background GC thread.*/
> err = f2fs_start_gc_thread(sbi);
> if (err)
> --
> 2.29.2
>