Re: [PATCH 2/2] f2fs: tune discard speed with storage usage rate

From: Chao Yu
Date: Tue Aug 14 2018 - 21:46:42 EST

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On 2018/8/15 1:23, Jaegeuk Kim wrote:
> On 08/14, Chao Yu wrote:
>> 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.
>
> So, we may need to distinguish low-end vs. high-end storage. In high-end case,
> it'd be better to avoid IO contention, while low-end device wants to get more
> discard commands as much as possible. So, how about adding an option for this
> as a tunable point?

Agreed, how about adding a sysfs entry discard_tunning:
1: enabled, use 4k granularity, self-adapted speed based on real device free space.
0: disabled, use dcc->discard_granularity, fixed speed.

By default: enabled

How do you think?

Thanks,

>
>>
>> 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@xxxxxxxxxx>
>>>> ---
>>>> 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
>>>
>>> .
>>>
>
> .
>

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In reply to: Jaegeuk Kim: "Re: [PATCH 2/2] f2fs: tune discard speed with storage usage rate"
Next in thread: Jaegeuk Kim: "Re: [PATCH 2/2] f2fs: tune discard speed with storage usage rate"
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