Re: [PATCH 2/2] f2fs: issue small discard by LBA order

[Chao Yu <chao@kernel.org>]

Hi Jaegeuk,

On 2018/7/7 7:23, Jaegeuk Kim wrote:
> On 07/05, Chao Yu wrote:
>> For small granularity discard which size is smaller than 64KB, if we
>> issue those kind of discards orderly by size, their IOs will be spread
>> into entire logical address, so that in FTL, L2P table will be updated
>> randomly, result bad wear rate in the table.
>>
>> In this patch, we choose to issue small discard by LBA order, by this
>> way, we can expect that L2P table updates from adjacent discard IOs can
>> be merged in the cache, so it can reduce lifetime wearing of flash.
>>
>> Signed-off-by: Chao Yu <yuchao0@huawei.com>
>> ---
>>  fs/f2fs/f2fs.h    |  2 ++
>>  fs/f2fs/segment.c | 71 +++++++++++++++++++++++++++++++++++++++++++++++
>>  2 files changed, 73 insertions(+)
>>
>> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
>> index 47ac0a9b022f..8d592029328a 100644
>> --- a/fs/f2fs/f2fs.h
>> +++ b/fs/f2fs/f2fs.h
>> @@ -290,6 +290,7 @@ struct discard_policy {
>>  	unsigned int io_aware_gran;	/* minimum granularity discard not be aware of I/O */
>>  	bool io_aware;			/* issue discard in idle time */
>>  	bool sync;			/* submit discard with REQ_SYNC flag */
>> +	bool ordered;			/* issue discard by lba order */
>>  	unsigned int granularity;	/* discard granularity */
>>  };
>>  
>> @@ -306,6 +307,7 @@ struct discard_cmd_control {
>>  	unsigned int max_discards;		/* max. discards to be issued */
>>  	unsigned int discard_granularity;	/* discard granularity */
>>  	unsigned int undiscard_blks;		/* # of undiscard blocks */
>> +	unsigned int next_pos;			/* next discard position */
>>  	atomic_t issued_discard;		/* # of issued discard */
>>  	atomic_t issing_discard;		/* # of issing discard */
>>  	atomic_t discard_cmd_cnt;		/* # of cached cmd count */
>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
>> index f95bf618bc1e..df0d91dfb8ac 100644
>> --- a/fs/f2fs/segment.c
>> +++ b/fs/f2fs/segment.c
>> @@ -18,6 +18,7 @@
>>  #include <linux/timer.h>
>>  #include <linux/freezer.h>
>>  #include <linux/sched/signal.h>
>> +#include <linux/delay.h>
> 
> Why?

I forgot to remove this... will do it.

> 
>>  
>>  #include "f2fs.h"
>>  #include "segment.h"
>> @@ -936,6 +937,7 @@ static void __init_discard_policy(struct f2fs_sb_info *sbi,
>>  	/* common policy */
>>  	dpolicy->type = discard_type;
>>  	dpolicy->sync = true;
>> +	dpolicy->ordered = false;
>>  	dpolicy->granularity = granularity;
>>  
>>  	dpolicy->max_requests = DEF_MAX_DISCARD_REQUEST;
>> @@ -947,6 +949,7 @@ static void __init_discard_policy(struct f2fs_sb_info *sbi,
>>  		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;
>> @@ -1202,6 +1205,69 @@ static int __queue_discard_cmd(struct f2fs_sb_info *sbi,
>>  	return 0;
>>  }
>>  
>> +static unsigned int __issue_discard_cmd_orderly(struct f2fs_sb_info *sbi,
>> +					struct discard_policy *dpolicy)
>> +{
>> +	struct discard_cmd_control *dcc = SM_I(sbi)->dcc_info;
>> +	struct discard_cmd *prev_dc = NULL, *next_dc = NULL;
>> +	struct rb_node **insert_p = NULL, *insert_parent = NULL;
>> +	struct discard_cmd *dc;
>> +	struct blk_plug plug;
>> +	unsigned int pos = dcc->next_pos;
>> +	unsigned int issued = 0, iter = 0;
>> +	bool io_interrupted;
>> +
>> +	mutex_lock(&dcc->cmd_lock);
>> +	dc = (struct discard_cmd *)f2fs_lookup_rb_tree_ret(&dcc->root,
>> +					NULL, pos,
>> +					(struct rb_entry **)&prev_dc,
>> +					(struct rb_entry **)&next_dc,
>> +					&insert_p, &insert_parent, true);
>> +	if (!dc)
>> +		dc = next_dc;
>> +
>> +	blk_start_plug(&plug);
>> +
>> +	while (dc) {
>> +		struct rb_node *node;
>> +
>> +		if (dc->state != D_PREP)
>> +			goto next;
>> +retry:
>> +		io_interrupted = false;
>> +
>> +		if (dpolicy->io_aware && !is_idle(sbi)) {
>> +			io_interrupted = true;
>> +			goto skip;
> 
> Please don't try, if user is doing something.

Just use 'break' instead of 'goto skip' here?

> 
>> +		}
>> +
>> +		__submit_discard_cmd(sbi, dpolicy, dc);
>> +		issued++;
>> +		dcc->next_pos = dc->lstart + dc->len;
>> +skip:
>> +		if (++iter >= dpolicy->max_requests)
>> +			break;
>> +
>> +		if (io_interrupted)
>> +			goto retry;
>> +next:
>> +		node = rb_next(&dc->rb_node);
>> +		dc = rb_entry_safe(node, struct discard_cmd, rb_node);
>> +	}
>> +
>> +	blk_finish_plug(&plug);
>> +
>> +	if (!dc)
>> +		dcc->next_pos = 0;
>> +
>> +	mutex_unlock(&dcc->cmd_lock);
>> +
>> +	if (!issued && io_interrupted)
>> +		issued = -1;
>> +
>> +	return issued;
>> +}
>> +
>>  static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
>>  					struct discard_policy *dpolicy)
>>  {
>> @@ -1215,6 +1281,10 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
>>  	for (i = MAX_PLIST_NUM - 1; i >= 0; i--) {
>>  		if (i + 1 < dpolicy->granularity)
>>  			break;
>> +
>> +		if (i < DEFAULT_DISCARD_GRANULARITY && dpolicy->ordered)
>> +			return __issue_discard_cmd_orderly(sbi, dpolicy);
> 
> So, at this moment, we usually expect there'd be a bunch of small candidates
> only, and thus, it'd be better to issue small chunks in LBA order?

Yes, that's right. :)

Thanks,

> 
>> +
>>  		pend_list = &dcc->pend_list[i];
>>  
>>  		mutex_lock(&dcc->cmd_lock);
>> @@ -1786,6 +1856,7 @@ static int create_discard_cmd_control(struct f2fs_sb_info *sbi)
>>  	dcc->nr_discards = 0;
>>  	dcc->max_discards = MAIN_SEGS(sbi) << sbi->log_blocks_per_seg;
>>  	dcc->undiscard_blks = 0;
>> +	dcc->next_pos = 0;
>>  	dcc->root = RB_ROOT;
>>  	dcc->rbtree_check = false;
>>  
>> -- 
>> 2.18.0.rc1