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Subject: Re: [PATCH 2/2] f2fs: tune discard speed with storage usage rate
To:     Jaegeuk Kim <jaegeuk@kernel.org>
CC:     <linux-f2fs-devel@lists.sourceforge.net>,
        <linux-kernel@vger.kernel.org>, <chao@kernel.org>
References: <20180810100806.9298-1-yuchao0@huawei.com>
 <20180810100806.9298-2-yuchao0@huawei.com>
 <20180814041906.GC52730@jaegeuk-macbookpro.roam.corp.google.com>
From:   Chao Yu <yuchao0@huawei.com>
Message-ID: <57d9b6ea-68a5-4736-0b34-74db539d8959@huawei.com>
Date:   Tue, 14 Aug 2018 15:41:13 +0800
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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.

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@huawei.com>
>> ---
>>  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
> 
> .
>