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Date: Fri, 6 Jul 2018 16:23:45 -0700
From: Jaegeuk Kim <jaegeuk@...nel.org>
To: Chao Yu <yuchao0@...wei.com>
Cc: linux-f2fs-devel@...ts.sourceforge.net,
linux-kernel@...r.kernel.org, chao@...nel.org
Subject: Re: [PATCH 2/2] f2fs: issue small discard by LBA order
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?
>
> #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.
> + }
> +
> + __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?
> +
> 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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