Message-ID: <20180816012340.GA11896@jaegeuk-macbookpro.roam.corp.google.com>
Date:   Wed, 15 Aug 2018 18:23:40 -0700
From:   Jaegeuk Kim <jaegeuk@...nel.org>
To:     Ju Hyung Park <qkrwngud825@...il.com>
Cc:     Chao Yu <yuchao0@...wei.com>, linux-kernel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [f2fs-dev] [PATCH 2/2] f2fs: tune discard speed with storage
 usage rate

On 08/15, Ju Hyung Park wrote:
> btrfs also distinguishes high/low end SSDs with mount option "ssd" and
> "ssd_spread".
> I believe there is no implementation inside btrfs to do it automatically.
> 
> Providing users an option with a well made documentation is acceptable imo.

Yeah, I was thinking about this as well. How about adding "-o disk=%s" where
%s can be ufs/emmc/ssd/low_ssd/nvme/...?
And, we also can decide the device type automatically w/ kmsg by default.

> 
> And I personally think, if the default goes to a dynamically deciding
> method, it should tell it to kmsg.
> 
> Thanks,
> 
> On Wed, Aug 15, 2018, 12:31 PM Chao Yu <yuchao0@...wei.com> wrote:
> 
> > On 2018/8/15 11:20, Jaegeuk Kim wrote:
> > > On 08/15, Chao Yu wrote:
> > >> On 2018/8/15 10:56, Jaegeuk Kim wrote:
> > >>> On 08/15, Chao Yu wrote:
> > >>>> On 2018/8/15 10:33, Jaegeuk Kim wrote:
> > >>>>> On 08/15, Chao Yu wrote:
> > >>>>>> 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?
> > >>>>>
> > >>>>> I don't think this is proper with a sysfs entry, since we already
> > know the
> > >>>>
> > >>>> You mean by storage capacity? <= 32GB means low-end?
> > >>>
> > >>> Yes, that's current condition to judge it. If there is any other
> > method, it'd be
> > >>
> > >> That would be hard code...
> > >>
> > >> Still I have not got any other method to do the judgment except
> > capacity.
> > >
> > > Maybe ufs or emmc?
> >
> > Yeah, that's may be a good way.
> >
> > I remember very initial version UFS has very poor discard performance, for
> > that
> > kind of storage, it will be not accurate?
> >
> > Let me check whether there is a flag to distinguish ufs/emmc.
> >
> > Thanks,
> >
> > >
> > >>
> > >> Thanks,
> > >>
> > >>> better to change it.
> > >>>
> > >>>>
> > >>>> Thanks,
> > >>>>
> > >>>>> device type when mounting the partition. We won't require to change
> > the policy
> > >>>>> on the fly. And, I still don't get to change the default.
> > >>>>>
> > >>>>>>
> > >>>>>> 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@...wei.com>
> > >>>>>>>>>> ---
> > >>>>>>>>>>  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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> > _______________________________________________
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> > Linux-f2fs-devel@...ts.sourceforge.net
> > https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
> >

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