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Message-ID: <20231120112702epcms2p4e4408fed82d4385624eb32b17880e613@epcms2p4>
Date: Mon, 20 Nov 2023 20:27:02 +0900
From: Yonggil Song <yonggil.song@...sung.com>
To: Jaegeuk Kim <jaegeuk@...nel.org>
CC: "chao@...nel.org" <chao@...nel.org>,
"corbet@....net" <corbet@....net>,
"linux-f2fs-devel@...ts.sourceforge.net"
<linux-f2fs-devel@...ts.sourceforge.net>,
"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Seokhwan Kim <sukka.kim@...sung.com>,
Daejun Park <daejun7.park@...sung.com>,
Siwoo Jung <siu.jung@...sung.com>
Subject: RE:(2) [f2fs-dev] [PATCH v1] f2fs: New victim selection for GC
>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?
>
Hi jaegeuk.
I didn't consider ATGC because this feature is only supported by zoned devices(LFS).
I didn't add ATGC exception handling because I'm only enabling this feature when
it's a zoned device, but should I?
>>
>> 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@...sung.com>
>> ---
>> 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
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