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Date: Fri, 6 Jul 2018 18:10:59 -0700
From: Jaegeuk Kim <jaegeuk@...nel.org>
To: Chao Yu <chao@...nel.org>
Cc: Chao Yu <yuchao0@...wei.com>,
linux-f2fs-devel@...ts.sourceforge.net,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] f2fs: issue small discard by LBA order
On 07/07, Chao Yu wrote:
> 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?
Yes, likewise as is.
>
> >
> >> + }
> >> +
> >> + __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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