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Date: Sat, 7 Jul 2018 08:08:03 +0800
From: Chao Yu <chao@...nel.org>
To: Jaegeuk Kim <jaegeuk@...nel.org>, Chao Yu <yuchao0@...wei.com>
Cc: linux-f2fs-devel@...ts.sourceforge.net,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] f2fs: issue small discard by LBA order
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@...wei.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
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