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Message-ID: <20170815034518.GA94478@jaegeuk-macbookpro.roam.corp.google.com>
Date: Mon, 14 Aug 2017 20:45:18 -0700
From: Jaegeuk Kim <jaegeuk@...nel.org>
To: Chao Yu <chao@...nel.org>
Cc: linux-f2fs-devel@...ts.sourceforge.net,
linux-kernel@...r.kernel.org, Chao Yu <yuchao0@...wei.com>
Subject: Re: [PATCH v4] f2fs: introduce discard_granularity sysfs entry
On 08/07, Chao Yu wrote:
> From: Chao Yu <yuchao0@...wei.com>
>
> Commit d618ebaf0aa8 ("f2fs: enable small discard by default") enables
> f2fs to issue 4K size discard in real-time discard mode. However, issuing
> smaller discard may cost more lifetime but releasing less free space in
> flash device. Since f2fs has ability of separating hot/cold data and
> garbage collection, we can expect that small-sized invalid region would
> expand soon with OPU, deletion or garbage collection on valid datas, so
> it's better to delay or skip issuing smaller size discards, it could help
> to reduce overmuch consumption of IO bandwidth and lifetime of flash
> storage.
>
> This patch makes f2fs selectng 64K size as its default minimal
> granularity, and issue discard with the size which is not smaller than
> minimal granularity. Also it exposes discard granularity as sysfs entry
> for configuration in different scenario.
Hi Chao,
I'd like to change the default value to 1 in order to keep the original
behavior, since we must avoid performance fluctuation after this single
patch. Instead, you probably can change the value through sysfs.
Thanks,
>
> Signed-off-by: Chao Yu <yuchao0@...wei.com>
> ---
> v4: minor change in commit log.
> Documentation/ABI/testing/sysfs-fs-f2fs | 9 +++++++++
> fs/f2fs/f2fs.h | 4 ++++
> fs/f2fs/segment.c | 23 ++++++++++++++++++++++-
> fs/f2fs/sysfs.c | 7 +++++++
> 4 files changed, 42 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/ABI/testing/sysfs-fs-f2fs b/Documentation/ABI/testing/sysfs-fs-f2fs
> index 84c606fb3ca4..c579ce5e0ef5 100644
> --- a/Documentation/ABI/testing/sysfs-fs-f2fs
> +++ b/Documentation/ABI/testing/sysfs-fs-f2fs
> @@ -57,6 +57,15 @@ Contact: "Jaegeuk Kim" <jaegeuk.kim@...sung.com>
> Description:
> Controls the issue rate of small discard commands.
>
> +What: /sys/fs/f2fs/<disk>/discard_granularity
> +Date: July 2017
> +Contact: "Chao Yu" <yuchao0@...wei.com>
> +Description:
> + Controls discard granularity of inner discard thread, inner thread
> + will not issue discards with size that is smaller than granularity.
> + The unit size is one block, now only support configuring in range
> + of [1, 512].
> +
> What: /sys/fs/f2fs/<disk>/max_victim_search
> Date: January 2014
> Contact: "Jaegeuk Kim" <jaegeuk.kim@...sung.com>
> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> index 0ccccbfdeeab..1bcaa93bfed7 100644
> --- a/fs/f2fs/f2fs.h
> +++ b/fs/f2fs/f2fs.h
> @@ -195,6 +195,9 @@ struct discard_entry {
> unsigned char discard_map[SIT_VBLOCK_MAP_SIZE]; /* segment discard bitmap */
> };
>
> +/* default discard granularity of inner discard thread, unit: block count */
> +#define DEFAULT_DISCARD_GRANULARITY 16
> +
> /* max discard pend list number */
> #define MAX_PLIST_NUM 512
> #define plist_idx(blk_num) ((blk_num) >= MAX_PLIST_NUM ? \
> @@ -240,6 +243,7 @@ struct discard_cmd_control {
> struct mutex cmd_lock;
> unsigned int nr_discards; /* # of discards in the list */
> unsigned int max_discards; /* max. discards to be issued */
> + unsigned int discard_granularity; /* discard granularity */
> unsigned int undiscard_blks; /* # of undiscard blocks */
> atomic_t issued_discard; /* # of issued discard */
> atomic_t issing_discard; /* # of issing discard */
> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> index 71c2e0ac13d7..f336f8c541f0 100644
> --- a/fs/f2fs/segment.c
> +++ b/fs/f2fs/segment.c
> @@ -1019,7 +1019,8 @@ static void __issue_discard_cmd(struct f2fs_sb_info *sbi, bool issue_cond)
> f2fs_bug_on(sbi,
> !__check_rb_tree_consistence(sbi, &dcc->root));
> blk_start_plug(&plug);
> - for (i = MAX_PLIST_NUM - 1; i >= 0; i--) {
> + for (i = MAX_PLIST_NUM - 1; i >= 0 &&
> + i >= dcc->discard_granularity - 1; i--) {
> pend_list = &dcc->pend_list[i];
> list_for_each_entry_safe(dc, tmp, pend_list, list) {
> f2fs_bug_on(sbi, dc->state != D_PREP);
> @@ -1035,6 +1036,24 @@ static void __issue_discard_cmd(struct f2fs_sb_info *sbi, bool issue_cond)
> mutex_unlock(&dcc->cmd_lock);
> }
>
> +static void __drop_discard_cmd(struct f2fs_sb_info *sbi)
> +{
> + struct discard_cmd_control *dcc = SM_I(sbi)->dcc_info;
> + struct list_head *pend_list;
> + struct discard_cmd *dc, *tmp;
> + int i;
> +
> + mutex_lock(&dcc->cmd_lock);
> + for (i = MAX_PLIST_NUM - 1; i >= 0; i--) {
> + pend_list = &dcc->pend_list[i];
> + list_for_each_entry_safe(dc, tmp, pend_list, list) {
> + f2fs_bug_on(sbi, dc->state != D_PREP);
> + __remove_discard_cmd(sbi, dc);
> + }
> + }
> + mutex_unlock(&dcc->cmd_lock);
> +}
> +
> static void __wait_one_discard_bio(struct f2fs_sb_info *sbi,
> struct discard_cmd *dc)
> {
> @@ -1117,6 +1136,7 @@ void stop_discard_thread(struct f2fs_sb_info *sbi)
> void f2fs_wait_discard_bios(struct f2fs_sb_info *sbi)
> {
> __issue_discard_cmd(sbi, false);
> + __drop_discard_cmd(sbi);
> __wait_discard_cmd(sbi, false);
> }
>
> @@ -1449,6 +1469,7 @@ static int create_discard_cmd_control(struct f2fs_sb_info *sbi)
> atomic_set(&dcc->discard_cmd_cnt, 0);
> dcc->nr_discards = 0;
> dcc->max_discards = MAIN_SEGS(sbi) << sbi->log_blocks_per_seg;
> + dcc->discard_granularity = DEFAULT_DISCARD_GRANULARITY;
> dcc->undiscard_blks = 0;
> dcc->root = RB_ROOT;
>
> diff --git a/fs/f2fs/sysfs.c b/fs/f2fs/sysfs.c
> index 045b948c7466..4e5a95e9e666 100644
> --- a/fs/f2fs/sysfs.c
> +++ b/fs/f2fs/sysfs.c
> @@ -152,6 +152,11 @@ static ssize_t f2fs_sbi_store(struct f2fs_attr *a,
> spin_unlock(&sbi->stat_lock);
> return count;
> }
> +
> + if (!strcmp(a->attr.name, "discard_granularity") &&
> + (t == 0 || t > MAX_PLIST_NUM))
> + return -EINVAL;
> +
> *ui = t;
>
> if (!strcmp(a->attr.name, "iostat_enable") && *ui == 0)
> @@ -241,6 +246,7 @@ F2FS_RW_ATTR(GC_THREAD, f2fs_gc_kthread, gc_no_gc_sleep_time, no_gc_sleep_time);
> F2FS_RW_ATTR(GC_THREAD, f2fs_gc_kthread, gc_idle, gc_idle);
> F2FS_RW_ATTR(SM_INFO, f2fs_sm_info, reclaim_segments, rec_prefree_segments);
> F2FS_RW_ATTR(DCC_INFO, discard_cmd_control, max_small_discards, max_discards);
> +F2FS_RW_ATTR(DCC_INFO, discard_cmd_control, discard_granularity, discard_granularity);
> F2FS_RW_ATTR(RESERVED_BLOCKS, f2fs_sb_info, reserved_blocks, reserved_blocks);
> F2FS_RW_ATTR(SM_INFO, f2fs_sm_info, batched_trim_sections, trim_sections);
> F2FS_RW_ATTR(SM_INFO, f2fs_sm_info, ipu_policy, ipu_policy);
> @@ -281,6 +287,7 @@ static struct attribute *f2fs_attrs[] = {
> ATTR_LIST(gc_idle),
> ATTR_LIST(reclaim_segments),
> ATTR_LIST(max_small_discards),
> + ATTR_LIST(discard_granularity),
> ATTR_LIST(batched_trim_sections),
> ATTR_LIST(ipu_policy),
> ATTR_LIST(min_ipu_util),
> --
> 2.14.0
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