Re: [PATCH 2/2] f2fs: tune discard speed with storage usage rate

[Jaegeuk Kim]

On 08/15, Chao Yu wrote:
> On 2018/8/15 1:23, Jaegeuk Kim wrote:
> > On 08/14, Chao Yu wrote:
> >> On 2018/8/14 12:19, Jaegeuk Kim wrote:
> >>> On 08/10, Chao Yu wrote:
> >>>> Previously, discard speed was fixed mostly, and in high usage rate
> >>>> device, we will speed up issuing discard, but it doesn't make sense
> >>>> that in a non-full filesystem, we still issue discard with slow speed.
> >>>
> >>> Could you please elaborate the problem in more detail? The speed depends
> >>> on how many candidates?
> >>
> >> undiscard blocks are all 4k granularity.
> >> a) utility: filesystem: 20% + undiscard blocks: 20% = flash storage: 40%
> >> b) utility: filesystem: 40% + undiscard blocks: 25% = flash storage: 65%
> >> c) utility: filesystem: 60% + undiscard blocks: 30% = flash storage: 100%
> >>
> >>
> >> 1. for case c), we need to speed up issuing discard based on utilization of
> >> "filesystem + undiscard" instead of just utilization of filesystem.
> >>
> >> -		if (utilization(sbi) > DEF_DISCARD_URGENT_UTIL) {
> >> -			dpolicy->granularity = 1;
> >> -			dpolicy->max_interval = DEF_MIN_DISCARD_ISSUE_TIME;
> >> -		}
> >>
> >> 2. If free space in storage touches therein threshold, performance will be very
> >> sensitive. In low-end storage, with high usage in space, even free space is
> >> reduced by 1%, performance will decrease a lot.
> > 
> > So, we may need to distinguish low-end vs. high-end storage. In high-end case,
> > it'd be better to avoid IO contention, while low-end device wants to get more
> > discard commands as much as possible. So, how about adding an option for this
> > as a tunable point?
> 
> Agreed, how about adding a sysfs entry discard_tunning:
> 1: enabled, use 4k granularity, self-adapted speed based on real device free space.
> 0: disabled, use dcc->discard_granularity, fixed speed.
> 
> By default: enabled
> 
> How do you think?

I don't think this is proper with a sysfs entry, since we already know the
device type when mounting the partition. We won't require to change the policy
on the fly. And, I still don't get to change the default.

> 
> Thanks,
> 
> > 
> >>
> >> IMO, in above cases, we'd better to issue discard with high speed for c), middle
> >> speed for b), and low speed for a).
> >>
> >> How do you think?
> >>
> >> Thanks,
> >>
> >>>
> >>> Thanks,
> >>>
> >>>>
> >>>> Anyway, it comes out undiscarded block makes FTL GC be lower efficient
> >>>> and causing high lifetime overhead.
> >>>>
> >>>> Let's tune discard speed as below:
> >>>>
> >>>> a. adjust default issue interval:
> >>>> 		original	after
> >>>> min_interval:	50ms		100ms
> >>>> mid_interval:	500ms		1000ms
> >>>> max_interval:	60000ms		10000ms
> >>>>
> >>>> b. if last time we stop issuing discard due to IO interruption of user,
> >>>> let's reset all {min,mid,max}_interval to default one.
> >>>>
> >>>> c. tune {min,mid,max}_interval with below calculation method:
> >>>>
> >>>> base_interval = default_interval / 10;
> >>>> total_interval = default_interval - base_interval;
> >>>> interval = base_interval + total_interval * (100 - dev_util) / 100;
> >>>>
> >>>> For example:
> >>>> min_interval (:100ms)
> >>>> dev_util (%)	interval (ms)
> >>>> 0		100
> >>>> 10		91
> >>>> 20		82
> >>>> 30		73
> >>>> ...
> >>>> 80		28
> >>>> 90		19
> >>>> 100		10
> >>>>
> >>>> Signed-off-by: Chao Yu <yuchao0@xxxxxxxxxx>
> >>>> ---
> >>>>  fs/f2fs/f2fs.h    | 11 ++++----
> >>>>  fs/f2fs/segment.c | 64 +++++++++++++++++++++++++++++++++++++----------
> >>>>  fs/f2fs/segment.h |  9 +++++++
> >>>>  fs/f2fs/super.c   |  2 +-
> >>>>  4 files changed, 67 insertions(+), 19 deletions(-)
> >>>>
> >>>> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> >>>> index 273ffdaf4891..a1dd2e1c3cb9 100644
> >>>> --- a/fs/f2fs/f2fs.h
> >>>> +++ b/fs/f2fs/f2fs.h
> >>>> @@ -185,10 +185,9 @@ enum {
> >>>>  
> >>>>  #define MAX_DISCARD_BLOCKS(sbi)		BLKS_PER_SEC(sbi)
> >>>>  #define DEF_MAX_DISCARD_REQUEST		8	/* issue 8 discards per round */
> >>>> -#define DEF_MIN_DISCARD_ISSUE_TIME	50	/* 50 ms, if exists */
> >>>> -#define DEF_MID_DISCARD_ISSUE_TIME	500	/* 500 ms, if device busy */
> >>>> -#define DEF_MAX_DISCARD_ISSUE_TIME	60000	/* 60 s, if no candidates */
> >>>> -#define DEF_DISCARD_URGENT_UTIL		80	/* do more discard over 80% */
> >>>> +#define DEF_MIN_DISCARD_ISSUE_TIME	100	/* 100 ms, if exists */
> >>>> +#define DEF_MID_DISCARD_ISSUE_TIME	1000	/* 1000 ms, if device busy */
> >>>> +#define DEF_MAX_DISCARD_ISSUE_TIME	10000	/* 10000 ms, if no candidates */
> >>>>  #define DEF_CP_INTERVAL			60	/* 60 secs */
> >>>>  #define DEF_IDLE_INTERVAL		5	/* 5 secs */
> >>>>  
> >>>> @@ -248,7 +247,8 @@ struct discard_entry {
> >>>>  };
> >>>>  
> >>>>  /* default discard granularity of inner discard thread, unit: block count */
> >>>> -#define DEFAULT_DISCARD_GRANULARITY		1
> >>>> +#define MID_DISCARD_GRANULARITY			16
> >>>> +#define MIN_DISCARD_GRANULARITY			1
> >>>>  
> >>>>  /* max discard pend list number */
> >>>>  #define MAX_PLIST_NUM		512
> >>>> @@ -330,6 +330,7 @@ struct discard_cmd_control {
> >>>>  	atomic_t discard_cmd_cnt;		/* # of cached cmd count */
> >>>>  	struct rb_root root;			/* root of discard rb-tree */
> >>>>  	bool rbtree_check;			/* config for consistence check */
> >>>> +	bool io_interrupted;			/* last state of io interrupted */
> >>>>  };
> >>>>  
> >>>>  /* for the list of fsync inodes, used only during recovery */
> >>>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> >>>> index 8b52e8dfb12f..9564aaf1f27b 100644
> >>>> --- a/fs/f2fs/segment.c
> >>>> +++ b/fs/f2fs/segment.c
> >>>> @@ -968,6 +968,44 @@ static void __check_sit_bitmap(struct f2fs_sb_info *sbi,
> >>>>  #endif
> >>>>  }
> >>>>  
> >>>> +static void __adjust_discard_speed(unsigned int *interval,
> >>>> +				unsigned int def_interval, int dev_util)
> >>>> +{
> >>>> +	unsigned int base_interval, total_interval;
> >>>> +
> >>>> +	base_interval = def_interval / 10;
> >>>> +	total_interval = def_interval - base_interval;
> >>>> +
> >>>> +	/*
> >>>> +	 * if def_interval = 100, adjusted interval should be in range of
> >>>> +	 * [10, 100].
> >>>> +	 */
> >>>> +	*interval = base_interval + total_interval * (100 - dev_util) / 100;
> >>>> +}
> >>>> +
> >>>> +static void __tune_discard_policy(struct f2fs_sb_info *sbi,
> >>>> +					struct discard_policy *dpolicy)
> >>>> +{
> >>>> +	struct discard_cmd_control *dcc = SM_I(sbi)->dcc_info;
> >>>> +	int dev_util;
> >>>> +
> >>>> +	if (dcc->io_interrupted) {
> >>>> +		dpolicy->min_interval = DEF_MIN_DISCARD_ISSUE_TIME;
> >>>> +		dpolicy->mid_interval = DEF_MID_DISCARD_ISSUE_TIME;
> >>>> +		dpolicy->max_interval = DEF_MAX_DISCARD_ISSUE_TIME;
> >>>> +		return;
> >>>> +	}
> >>>> +
> >>>> +	dev_util = dev_utilization(sbi);
> >>>> +
> >>>> +	__adjust_discard_speed(&dpolicy->min_interval,
> >>>> +				DEF_MIN_DISCARD_ISSUE_TIME, dev_util);
> >>>> +	__adjust_discard_speed(&dpolicy->mid_interval,
> >>>> +				DEF_MID_DISCARD_ISSUE_TIME, dev_util);
> >>>> +	__adjust_discard_speed(&dpolicy->max_interval,
> >>>> +				DEF_MAX_DISCARD_ISSUE_TIME, dev_util);
> >>>> +}
> >>>> +
> >>>>  static void __init_discard_policy(struct f2fs_sb_info *sbi,
> >>>>  				struct discard_policy *dpolicy,
> >>>>  				int discard_type, unsigned int granularity)
> >>>> @@ -982,20 +1020,11 @@ static void __init_discard_policy(struct f2fs_sb_info *sbi,
> >>>>  	dpolicy->io_aware_gran = MAX_PLIST_NUM;
> >>>>  
> >>>>  	if (discard_type == DPOLICY_BG) {
> >>>> -		dpolicy->min_interval = DEF_MIN_DISCARD_ISSUE_TIME;
> >>>> -		dpolicy->mid_interval = DEF_MID_DISCARD_ISSUE_TIME;
> >>>> -		dpolicy->max_interval = DEF_MAX_DISCARD_ISSUE_TIME;
> >>>>  		dpolicy->io_aware = true;
> >>>>  		dpolicy->sync = false;
> >>>>  		dpolicy->ordered = true;
> >>>> -		if (utilization(sbi) > DEF_DISCARD_URGENT_UTIL) {
> >>>> -			dpolicy->granularity = 1;
> >>>> -			dpolicy->max_interval = DEF_MIN_DISCARD_ISSUE_TIME;
> >>>> -		}
> >>>> +		__tune_discard_policy(sbi, dpolicy);
> >>>>  	} else if (discard_type == DPOLICY_FORCE) {
> >>>> -		dpolicy->min_interval = DEF_MIN_DISCARD_ISSUE_TIME;
> >>>> -		dpolicy->mid_interval = DEF_MID_DISCARD_ISSUE_TIME;
> >>>> -		dpolicy->max_interval = DEF_MAX_DISCARD_ISSUE_TIME;
> >>>>  		dpolicy->io_aware = false;
> >>>>  	} else if (discard_type == DPOLICY_FSTRIM) {
> >>>>  		dpolicy->io_aware = false;
> >>>> @@ -1353,6 +1382,8 @@ static unsigned int __issue_discard_cmd_orderly(struct f2fs_sb_info *sbi,
> >>>>  	if (!issued && io_interrupted)
> >>>>  		issued = -1;
> >>>>  
> >>>> +	dcc->io_interrupted = io_interrupted;
> >>>> +
> >>>>  	return issued;
> >>>>  }
> >>>>  
> >>>> @@ -1370,7 +1401,7 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
> >>>>  		if (i + 1 < dpolicy->granularity)
> >>>>  			break;
> >>>>  
> >>>> -		if (i < DEFAULT_DISCARD_GRANULARITY && dpolicy->ordered)
> >>>> +		if (i < MID_DISCARD_GRANULARITY && dpolicy->ordered)
> >>>>  			return __issue_discard_cmd_orderly(sbi, dpolicy);
> >>>>  
> >>>>  		pend_list = &dcc->pend_list[i];
> >>>> @@ -1407,6 +1438,8 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
> >>>>  	if (!issued && io_interrupted)
> >>>>  		issued = -1;
> >>>>  
> >>>> +	dcc->io_interrupted = io_interrupted;
> >>>> +
> >>>>  	return issued;
> >>>>  }
> >>>>  
> >>>> @@ -1576,7 +1609,11 @@ static int issue_discard_thread(void *data)
> >>>>  	struct f2fs_sb_info *sbi = data;
> >>>>  	struct discard_cmd_control *dcc = SM_I(sbi)->dcc_info;
> >>>>  	wait_queue_head_t *q = &dcc->discard_wait_queue;
> >>>> -	struct discard_policy dpolicy;
> >>>> +	struct discard_policy dpolicy = {
> >>>> +		.min_interval = DEF_MIN_DISCARD_ISSUE_TIME,
> >>>> +		.mid_interval = DEF_MID_DISCARD_ISSUE_TIME,
> >>>> +		.max_interval = DEF_MAX_DISCARD_ISSUE_TIME,
> >>>> +	};
> >>>>  	unsigned int wait_ms = DEF_MIN_DISCARD_ISSUE_TIME;
> >>>>  	int issued;
> >>>>  
> >>>> @@ -1929,7 +1966,7 @@ static int create_discard_cmd_control(struct f2fs_sb_info *sbi)
> >>>>  	if (!dcc)
> >>>>  		return -ENOMEM;
> >>>>  
> >>>> -	dcc->discard_granularity = DEFAULT_DISCARD_GRANULARITY;
> >>>> +	dcc->discard_granularity = MIN_DISCARD_GRANULARITY;
> >>>>  	INIT_LIST_HEAD(&dcc->entry_list);
> >>>>  	for (i = 0; i < MAX_PLIST_NUM; i++)
> >>>>  		INIT_LIST_HEAD(&dcc->pend_list[i]);
> >>>> @@ -1945,6 +1982,7 @@ static int create_discard_cmd_control(struct f2fs_sb_info *sbi)
> >>>>  	dcc->next_pos = 0;
> >>>>  	dcc->root = RB_ROOT;
> >>>>  	dcc->rbtree_check = false;
> >>>> +	dcc->io_interrupted = false;
> >>>>  
> >>>>  	init_waitqueue_head(&dcc->discard_wait_queue);
> >>>>  	SM_I(sbi)->dcc_info = dcc;
> >>>> diff --git a/fs/f2fs/segment.h b/fs/f2fs/segment.h
> >>>> index 422b0ceb1eaa..63b4da72cd34 100644
> >>>> --- a/fs/f2fs/segment.h
> >>>> +++ b/fs/f2fs/segment.h
> >>>> @@ -616,6 +616,15 @@ static inline int utilization(struct f2fs_sb_info *sbi)
> >>>>  					sbi->user_block_count);
> >>>>  }
> >>>>  
> >>>> +static inline int dev_utilization(struct f2fs_sb_info *sbi)
> >>>> +{
> >>>> +	unsigned int dev_blks;
> >>>> +
> >>>> +	dev_blks = valid_user_blocks(sbi) + SM_I(sbi)->dcc_info->undiscard_blks;
> >>>> +	return div_u64((u64)dev_blks * 100,
> >>>> +			MAIN_SEGS(sbi) << sbi->log_blocks_per_seg);
> >>>> +}
> >>>> +
> >>>>  /*
> >>>>   * Sometimes f2fs may be better to drop out-of-place update policy.
> >>>>   * And, users can control the policy through sysfs entries.
> >>>> diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
> >>>> index b055f2ea77c5..55ed76daad23 100644
> >>>> --- a/fs/f2fs/super.c
> >>>> +++ b/fs/f2fs/super.c
> >>>> @@ -2862,7 +2862,7 @@ static void f2fs_tuning_parameters(struct f2fs_sb_info *sbi)
> >>>>  	/* adjust parameters according to the volume size */
> >>>>  	if (sm_i->main_segments <= SMALL_VOLUME_SEGMENTS) {
> >>>>  		F2FS_OPTION(sbi).alloc_mode = ALLOC_MODE_REUSE;
> >>>> -		sm_i->dcc_info->discard_granularity = 1;
> >>>> +		sm_i->dcc_info->discard_granularity = MIN_DISCARD_GRANULARITY;
> >>>>  		sm_i->ipu_policy = 1 << F2FS_IPU_FORCE;
> >>>>  	}
> >>>>  
> >>>> -- 
> >>>> 2.18.0.rc1
> >>>
> >>> .
> >>>
> > 
> > .
> >