Re: [f2fs-dev] [PATCH v1] f2fs: New victim selection for GC

From: Jaegeuk Kim
Date: Fri Nov 17 2023 - 12:34:48 EST

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Hi Yonggil,

On 10/26, Yonggil Song wrote:
> Overview
> ========
>
> Introduce a new way to select the data section first when selecting a
> victim in foreground GC. This victim selection method works when the
> prefer_data_victim mount option is enabled. If foreground GC migrates only
> data sections and runs out of free sections, it cleans dirty node sections
> to get more free sections.
>
> Problem
> =======
>
> If the total amount of nodes is larger than the size of one section, nodes
> occupy multiple sections, and node victims are often selected because the
> gc cost is lowered by data block migration in foreground gc. Since moving
> the data section causes frequent node victim selection, victim threshing
> occurs in the node section. This results in an increase in WAF.

How does that work w/ ATGC?

>
> Experiment
> ==========
>
> Test environment is as follows.
>
> System info
> - 3.6GHz, 16 core CPU
> - 36GiB Memory
> Device info
> - a conventional null_blk with 228MiB
> - a sequential null_blk with 4068 zones of 8MiB
> Format
> - mkfs.f2fs <conv null_blk> -c <seq null_blk> -m -Z 8 -o 3.89
> Mount
> - mount -o prefer_data_victim <conv null_blk> <mount point>
> Fio script
> - fio --rw=randwrite --bs=4k --ba=4k --filesize=31187m --norandommap --overwrite=1 --name=job1 --filename=./mnt/sustain --io_size=128g
> WAF calculation
> - (IOs on conv. null_blk + IOs on seq. null_blk) / random write IOs
>
> Conclusion
> ==========
>
> This experiment showed that the WAF was reduced by 29% (18.75 -> 13.3) when
> the data section was selected first when selecting GC victims. This was
> achieved by reducing the migration of the node blocks by 69.4%
> (253,131,743 blks -> 77,463,278 blks). It is possible to achieve low WAF
> performance with the GC victim selection method in environments where the
> section size is relatively small.
>
> Signed-off-by: Yonggil Song <yonggil.song@xxxxxxxxxxx>
> ---
> Documentation/filesystems/f2fs.rst | 3 +
> fs/f2fs/f2fs.h | 2 +
> fs/f2fs/gc.c | 100 +++++++++++++++++++++++------
> fs/f2fs/segment.h | 2 +
> fs/f2fs/super.c | 9 +++
> 5 files changed, 95 insertions(+), 21 deletions(-)
>
> diff --git a/Documentation/filesystems/f2fs.rst b/Documentation/filesystems/f2fs.rst
> index d32c6209685d..58e6d001d7ab 100644
> --- a/Documentation/filesystems/f2fs.rst
> +++ b/Documentation/filesystems/f2fs.rst
> @@ -367,6 +367,9 @@ errors=%s Specify f2fs behavior on critical errors. This supports modes:
> pending node write drop keep N/A
> pending meta write keep keep N/A
> ====================== =============== =============== ========
> +prefer_data_victim When selecting victims in foreground GC, victims of data type
> + are prioritized. This option minimizes GC victim threshing
> + in the node section to reduce WAF.
> ======================== ============================================================
>
> Debugfs Entries
> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> index 6d688e42d89c..8b31fa2ea09a 100644
> --- a/fs/f2fs/f2fs.h
> +++ b/fs/f2fs/f2fs.h
> @@ -108,6 +108,7 @@ extern const char *f2fs_fault_name[FAULT_MAX];
> #define F2FS_MOUNT_GC_MERGE 0x02000000
> #define F2FS_MOUNT_COMPRESS_CACHE 0x04000000
> #define F2FS_MOUNT_AGE_EXTENT_CACHE 0x08000000
> +#define F2FS_MOUNT_PREFER_DATA_VICTIM 0x10000000
>
> #define F2FS_OPTION(sbi) ((sbi)->mount_opt)
> #define clear_opt(sbi, option) (F2FS_OPTION(sbi).opt &= ~F2FS_MOUNT_##option)
> @@ -1648,6 +1649,7 @@ struct f2fs_sb_info {
> struct f2fs_mount_info mount_opt; /* mount options */
>
> /* for cleaning operations */
> + bool need_node_clean; /* only used for prefer_data_victim */
> struct f2fs_rwsem gc_lock; /*
> * semaphore for GC, avoid
> * race between GC and GC or CP
> diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
> index f550cdeaa663..8a2da808a5fb 100644
> --- a/fs/f2fs/gc.c
> +++ b/fs/f2fs/gc.c
> @@ -752,6 +752,8 @@ int f2fs_get_victim(struct f2fs_sb_info *sbi, unsigned int *result,
> unsigned int last_segment;
> unsigned int nsearched;
> bool is_atgc;
> + bool is_prefer_data_victim =
> + test_opt(sbi, PREFER_DATA_VICTIM) && gc_type == FG_GC;
> int ret = 0;
>
> mutex_lock(&dirty_i->seglist_lock);
> @@ -767,6 +769,11 @@ int f2fs_get_victim(struct f2fs_sb_info *sbi, unsigned int *result,
> p.oldest_age = 0;
> p.min_cost = get_max_cost(sbi, &p);
>
> + if (is_prefer_data_victim) {
> + p.node_min_cost = p.min_cost;
> + p.node_min_segno = p.min_segno;
> + }
> +
> is_atgc = (p.gc_mode == GC_AT || p.alloc_mode == AT_SSR);
> nsearched = 0;
>
> @@ -884,9 +891,25 @@ int f2fs_get_victim(struct f2fs_sb_info *sbi, unsigned int *result,
>
> cost = get_gc_cost(sbi, segno, &p);
>
> - if (p.min_cost > cost) {
> - p.min_segno = segno;
> - p.min_cost = cost;
> + if (is_prefer_data_victim) {
> + if (IS_DATASEG(get_seg_entry(sbi, segno)->type)) {
> + /* update data segments victim */
> + if (p.min_cost > cost) {
> + p.min_segno = segno;
> + p.min_cost = cost;
> + }
> + } else {
> + /* update node segments victim */
> + if (p.node_min_cost > cost) {
> + p.node_min_segno = segno;
> + p.node_min_cost = cost;
> + }
> + }
> + } else {
> + if (p.min_cost > cost) {
> + p.min_segno = segno;
> + p.min_cost = cost;
> + }
> }
> next:
> if (nsearched >= p.max_search) {
> @@ -901,6 +924,25 @@ int f2fs_get_victim(struct f2fs_sb_info *sbi, unsigned int *result,
> }
> }
>
> + if (is_prefer_data_victim && sbi->need_node_clean) {
> + /* we need to clean node sections */
> + if (p.min_cost > p.node_min_cost) {
> + p.min_segno = p.node_min_segno;
> + p.min_cost = p.node_min_cost;
> + } else {
> + /*
> + * data victim cost is the lowest.
> + * if free sections are enough, stop cleaning node victim.
> + * if not, it goes on by GCing data victims.
> + */
> + if (has_enough_free_secs(sbi, prefree_segments(sbi), 0)) {
> + sbi->need_node_clean = false;
> + p.min_segno = NULL_SEGNO;
> + goto out;
> + }
> + }
> + }
> +
> /* get victim for GC_AT/AT_SSR */
> if (is_atgc) {
> lookup_victim_by_age(sbi, &p);
> @@ -1830,8 +1872,27 @@ int f2fs_gc(struct f2fs_sb_info *sbi, struct f2fs_gc_control *gc_control)
> goto stop;
> }
>
> + __get_secs_required(sbi, NULL, &upper_secs, NULL);
> +
> + /*
> + * Write checkpoint to reclaim prefree segments.
> + * We need more three extra sections for writer's data/node/dentry.
> + */
> + if (free_sections(sbi) <= upper_secs + NR_GC_CHECKPOINT_SECS) {
> + if (test_opt(sbi, PREFER_DATA_VICTIM)) {
> + sbi->need_node_clean = true;
> + }
> + if (prefree_segments(sbi)) {
> + ret = f2fs_write_checkpoint(sbi, &cpc);
> + if (ret)
> + goto stop;
> + /* Reset due to checkpoint */
> + sec_freed = 0;
> + }
> + }
> +
> /* Let's run FG_GC, if we don't have enough space. */
> - if (has_not_enough_free_secs(sbi, 0, 0)) {
> + if (gc_type == BG_GC && has_not_enough_free_secs(sbi, 0, 0)) {
> gc_type = FG_GC;
>
> /*
> @@ -1882,7 +1943,17 @@ int f2fs_gc(struct f2fs_sb_info *sbi, struct f2fs_gc_control *gc_control)
> if (!gc_control->no_bg_gc &&
> total_sec_freed < gc_control->nr_free_secs)
> goto go_gc_more;
> - goto stop;
> + if (test_opt(sbi, PREFER_DATA_VICTIM)) {
> + /*
> + * If the need_node_clean flag is set
> + * even though there are enough free
> + * sections, node cleaning will continue.
> + */
> + if (!sbi->need_node_clean)
> + goto stop;
> + } else {
> + goto stop;
> + }
> }
> if (sbi->skipped_gc_rwsem)
> skipped_round++;
> @@ -1897,21 +1968,6 @@ int f2fs_gc(struct f2fs_sb_info *sbi, struct f2fs_gc_control *gc_control)
> goto stop;
> }
>
> - __get_secs_required(sbi, NULL, &upper_secs, NULL);
> -
> - /*
> - * Write checkpoint to reclaim prefree segments.
> - * We need more three extra sections for writer's data/node/dentry.
> - */
> - if (free_sections(sbi) <= upper_secs + NR_GC_CHECKPOINT_SECS &&
> - prefree_segments(sbi)) {
> - stat_inc_cp_call_count(sbi, TOTAL_CALL);
> - ret = f2fs_write_checkpoint(sbi, &cpc);
> - if (ret)
> - goto stop;
> - /* Reset due to checkpoint */
> - sec_freed = 0;
> - }
> go_gc_more:
> segno = NULL_SEGNO;
> goto gc_more;
> @@ -1920,8 +1976,10 @@ int f2fs_gc(struct f2fs_sb_info *sbi, struct f2fs_gc_control *gc_control)
> SIT_I(sbi)->last_victim[ALLOC_NEXT] = 0;
> SIT_I(sbi)->last_victim[FLUSH_DEVICE] = gc_control->victim_segno;
>
> - if (gc_type == FG_GC)
> + if (gc_type == FG_GC) {
> f2fs_unpin_all_sections(sbi, true);
> + sbi->need_node_clean = false;
> + }
>
> trace_f2fs_gc_end(sbi->sb, ret, total_freed, total_sec_freed,
> get_pages(sbi, F2FS_DIRTY_NODES),
> diff --git a/fs/f2fs/segment.h b/fs/f2fs/segment.h
> index 2ca8fb5d0dc4..d55fa1fee2e0 100644
> --- a/fs/f2fs/segment.h
> +++ b/fs/f2fs/segment.h
> @@ -197,8 +197,10 @@ struct victim_sel_policy {
> unsigned int offset; /* last scanned bitmap offset */
> unsigned int ofs_unit; /* bitmap search unit */
> unsigned int min_cost; /* minimum cost */
> + unsigned int node_min_cost; /* minimum cost of node type section */
> unsigned long long oldest_age; /* oldest age of segments having the same min cost */
> unsigned int min_segno; /* segment # having min. cost */
> + unsigned int node_min_segno; /* node segment # having min. cost */
> unsigned long long age; /* mtime of GCed section*/
> unsigned long long age_threshold;/* age threshold */
> };
> diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
> index a8c8232852bb..133137dd6fd0 100644
> --- a/fs/f2fs/super.c
> +++ b/fs/f2fs/super.c
> @@ -165,6 +165,7 @@ enum {
> Opt_memory_mode,
> Opt_age_extent_cache,
> Opt_errors,
> + Opt_prefer_data_victim,
> Opt_err,
> };
>
> @@ -245,6 +246,7 @@ static match_table_t f2fs_tokens = {
> {Opt_memory_mode, "memory=%s"},
> {Opt_age_extent_cache, "age_extent_cache"},
> {Opt_errors, "errors=%s"},
> + {Opt_prefer_data_victim, "prefer_data_victim"},
> {Opt_err, NULL},
> };
>
> @@ -1286,6 +1288,13 @@ static int parse_options(struct super_block *sb, char *options, bool is_remount)
> }
> kfree(name);
> break;
> + case Opt_prefer_data_victim:
> + if (!f2fs_sb_has_blkzoned(sbi)) {
> + f2fs_err(sbi, "prefer_data_victim is only allowed with zoned block device feature");
> + return -EINVAL;
> + }
> + set_opt(sbi, PREFER_DATA_VICTIM);
> + break;
> default:
> f2fs_err(sbi, "Unrecognized mount option \"%s\" or missing value",
> p);
> --
> 2.34.1

Next message: Sui Jingfeng: "Re: [PATCH 8/8] drm/bridge: it66121: Allow link this driver as a lib"
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Next in thread: Yonggil Song: "RE:(2) [f2fs-dev] [PATCH v1] f2fs: New victim selection for GC"
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