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SubjectRe: [PATCH v4] f2fs: introduce discard_granularity sysfs entry
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Hi Jaegeuk,

Sorry for the delay, the modification looks good to me. ;)

Thanks,

On 2017/8/16 1:54, Jaegeuk Kim wrote:
> On 08/15, Chao Yu wrote:
>> On 2017/8/15 11:45, Jaegeuk Kim wrote:
>>> On 08/07, Chao Yu wrote:
>>>> From: Chao Yu <yuchao0@huawei.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.
>>
>> As I know, in fragmented filesystem space, there are may dozens of thousand
>> discard, in scenario of cellphone user are using, 30% is above 64K size, but
>> occupy 75% space of all undiscard space, so I changed discard_granularity to 64K
>> just to release bulk space in device. For other small-sized discards, I expect
>> that they may extend and cross the granularity threshold soon, and fstrim of
>> android could cover them in the night.
>
> Yup, I thought that, but this patch prevents fstrim from issuing small discards
> due to the granularity check. And, low-end device likes to issue small discards
> much more. How about this?
>
> From a0f38a8574a35995ba9e9e81ae5138919bb672a8 Mon Sep 17 00:00:00 2001
> From: Chao Yu <yuchao0@huawei.com>
> Date: Mon, 7 Aug 2017 23:09:56 +0800
> Subject: [PATCH] f2fs: introduce discard_granularity sysfs entry
>
> 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.
>
> Jaegeuk Kim:
> We must issue all the accumulated discard commands when fstrim is called.
> So, I've added pend_list_tag[] to indicate whether we should issue the
> commands or not. If tag sets P_ACTIVE or P_TRIM, we have to issue them.
> P_TRIM is set once at a time, given fstrim trigger.
>
> Signed-off-by: Chao Yu <yuchao0@huawei.com>
> Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
> ---
> Documentation/ABI/testing/sysfs-fs-f2fs | 9 +++++++
> fs/f2fs/f2fs.h | 9 +++++++
> fs/f2fs/segment.c | 43 +++++++++++++++++++++++++++++++--
> fs/f2fs/sysfs.c | 23 ++++++++++++++++++
> 4 files changed, 82 insertions(+), 2 deletions(-)
>
> diff --git a/Documentation/ABI/testing/sysfs-fs-f2fs b/Documentation/ABI/testing/sysfs-fs-f2fs
> index 621da3fc56c5..11b7f4ebea7c 100644
> --- a/Documentation/ABI/testing/sysfs-fs-f2fs
> +++ b/Documentation/ABI/testing/sysfs-fs-f2fs
> @@ -57,6 +57,15 @@ Contact: "Jaegeuk Kim" <jaegeuk.kim@samsung.com>
> Description:
> Controls the issue rate of small discard commands.
>
> +What: /sys/fs/f2fs/<disk>/discard_granularity
> +Date: July 2017
> +Contact: "Chao Yu" <yuchao0@huawei.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@samsung.com>
> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> index e252e5bf9791..336021b9b93e 100644
> --- a/fs/f2fs/f2fs.h
> +++ b/fs/f2fs/f2fs.h
> @@ -196,11 +196,18 @@ 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 ? \
> (MAX_PLIST_NUM - 1) : (blk_num - 1))
>
> +#define P_ACTIVE 0x01
> +#define P_TRIM 0x02
> +#define plist_issue(tag) (((tag) & P_ACTIVE) || ((tag) & P_TRIM))
> +
> enum {
> D_PREP,
> D_SUBMIT,
> @@ -236,11 +243,13 @@ struct discard_cmd_control {
> struct task_struct *f2fs_issue_discard; /* discard thread */
> struct list_head entry_list; /* 4KB discard entry list */
> struct list_head pend_list[MAX_PLIST_NUM];/* store pending entries */
> + unsigned char pend_list_tag[MAX_PLIST_NUM];/* tag for pending entries */
> struct list_head wait_list; /* store on-flushing entries */
> wait_queue_head_t discard_wait_queue; /* waiting queue for wake-up */
> 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 05144b3a7f62..8c90b69dcd6d 100644
> --- a/fs/f2fs/segment.c
> +++ b/fs/f2fs/segment.c
> @@ -1028,22 +1028,49 @@ 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 && plist_issue(dcc->pend_list_tag[i]); 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);
>
> + /* Hurry up to finish fstrim */
> + if (dcc->pend_list_tag[i] & P_TRIM) {
> + __submit_discard_cmd(sbi, dc);
> + continue;
> + }
> +
> if (!issue_cond || is_idle(sbi))
> __submit_discard_cmd(sbi, dc);
> if (issue_cond && iter++ > DISCARD_ISSUE_RATE)
> goto out;
> }
> + if (list_empty(pend_list) && dcc->pend_list_tag[i] & P_TRIM)
> + dcc->pend_list_tag[i] &= (~P_TRIM);
> }
> out:
> blk_finish_plug(&plug);
> 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)
> {
> @@ -1126,6 +1153,7 @@ 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);
> }
>
> @@ -1448,9 +1476,13 @@ static int create_discard_cmd_control(struct f2fs_sb_info *sbi)
> if (!dcc)
> return -ENOMEM;
>
> + dcc->discard_granularity = DEFAULT_DISCARD_GRANULARITY;
> INIT_LIST_HEAD(&dcc->entry_list);
> - for (i = 0; i < MAX_PLIST_NUM; i++)
> + for (i = 0; i < MAX_PLIST_NUM; i++) {
> INIT_LIST_HEAD(&dcc->pend_list[i]);
> + if (i >= dcc->discard_granularity - 1)
> + dcc->pend_list_tag[i] |= P_ACTIVE;
> + }
> INIT_LIST_HEAD(&dcc->wait_list);
> mutex_init(&dcc->cmd_lock);
> atomic_set(&dcc->issued_discard, 0);
> @@ -2079,11 +2111,13 @@ bool exist_trim_candidates(struct f2fs_sb_info *sbi, struct cp_control *cpc)
>
> int f2fs_trim_fs(struct f2fs_sb_info *sbi, struct fstrim_range *range)
> {
> + struct discard_cmd_control *dcc = SM_I(sbi)->dcc_info;
> __u64 start = F2FS_BYTES_TO_BLK(range->start);
> __u64 end = start + F2FS_BYTES_TO_BLK(range->len) - 1;
> unsigned int start_segno, end_segno;
> struct cp_control cpc;
> int err = 0;
> + int i;
>
> if (start >= MAX_BLKADDR(sbi) || range->len < sbi->blocksize)
> return -EINVAL;
> @@ -2127,6 +2161,11 @@ int f2fs_trim_fs(struct f2fs_sb_info *sbi, struct fstrim_range *range)
>
> schedule();
> }
> + /* It's time to issue all the filed discards */
> + mutex_lock(&dcc->cmd_lock);
> + for (i = 0; i < MAX_PLIST_NUM; i++)
> + dcc->pend_list_tag[i] |= P_TRIM;
> + mutex_unlock(&dcc->cmd_lock);
> out:
> range->len = F2FS_BLK_TO_BYTES(cpc.trimmed);
> return err;
> diff --git a/fs/f2fs/sysfs.c b/fs/f2fs/sysfs.c
> index c40e5d24df9f..4bcaa9059026 100644
> --- a/fs/f2fs/sysfs.c
> +++ b/fs/f2fs/sysfs.c
> @@ -152,6 +152,27 @@ static ssize_t f2fs_sbi_store(struct f2fs_attr *a,
> spin_unlock(&sbi->stat_lock);
> return count;
> }
> +
> + if (!strcmp(a->attr.name, "discard_granularity")) {
> + struct discard_cmd_control *dcc = SM_I(sbi)->dcc_info;
> + int i;
> +
> + if (t == 0 || t > MAX_PLIST_NUM)
> + return -EINVAL;
> + if (t == *ui)
> + return count;
> +
> + mutex_lock(&dcc->cmd_lock);
> + for (i = 0; i < MAX_PLIST_NUM; i++) {
> + if (i >= t - 1)
> + dcc->pend_list_tag[i] |= P_ACTIVE;
> + else
> + dcc->pend_list_tag[i] &= (~P_ACTIVE);
> + }
> + mutex_unlock(&dcc->cmd_lock);
> + return count;
> + }
> +
> *ui = t;
>
> if (!strcmp(a->attr.name, "iostat_enable") && *ui == 0)
> @@ -248,6 +269,7 @@ F2FS_RW_ATTR(GC_THREAD, f2fs_gc_kthread, gc_idle, gc_idle);
> F2FS_RW_ATTR(GC_THREAD, f2fs_gc_kthread, gc_urgent, gc_urgent);
> 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);
> @@ -290,6 +312,7 @@ static struct attribute *f2fs_attrs[] = {
> ATTR_LIST(gc_urgent),
> 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),
>

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