Re: [PATCH v3] fat: Batched discard support for fat

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On Mon, 28 Feb 2011, Kyungmin Park wrote:

> On Fri, Feb 25, 2011 at 8:17 PM, Lukas Czerner <lczerner@xxxxxxxxxx> wrote:
> > On Fri, 25 Feb 2011, Kyungmin Park wrote:
> >
> >> From: Kyungmin Park <kyungmin.park@xxxxxxxxxxx>
> >>
> >> FAT supports batched discard as ext4.
> >>
> >> Cited from Lukas words.
> >> "The current solution is not ideal because of its bad performance impact.
> >> So basic idea to improve things is to avoid discarding every time some
> >> blocks are freed. and instead batching is together into bigger trims,
> >> which tends to be more effective."
> >>
> >> You can find an information in detail at following URLs.
> >> http://lwn.net/Articles/397538/
> >> http://lwn.net/Articles/383933/
> >>
> >> Clearify the meaning of "len" (Cited form Lukas mail)
> >>
> >> Let the "O" be free (bytes, blocks, whatever), and "=" be used.
> >> Now, we have a filesystem like this.
> >>
> >>   OOOO==O===OO===OOOOO==O===O===OOOOOOO===
> >>   ^                                      ^
> >>   0                                      40
> >>
> >> This is how it supposed to wotk if you have called FITIRM with parameters:
> >>
> >> start = 0
> >> minlen = 2
> >> len = 20
> >>
> >> So you will go through (blocks, bytes...) 0 -> 20
> >>
> >>   OOOO==O===OO===OOOOO==O===O===OOOOOOO===
> >>   ^                   ^
> >>   0                   20
> >>
> >> So, you will call discard on extents:
> >>
> >> 0-3
> >> You'll skip 6 because is smaller than minlen
> >> 10-11
> >> 15-19
> >>
> >> instead of
> >>
> >> 0-3
> >> 10-11
> >> 15-19
> >> 30-36
> >
> > Hi thanks for the next version. And again I have to ask: Did you test it
> > ? and how ? Did you tried xfstest No. 251 ? Couple of comments bellow.
> 
> I tested it with your test program. Of course I modified for our
> environment (eMMC).

Ok, good.

> 
> #include <errno.h>
> #include <fcntl.h>
> #include <stdio.h>
> #include <stdint.h>
> #include <sys/ioctl.h>
> 
> struct fstrim_range {
>         uint64_t start;
>         uint64_t len;
>         uint64_t minlen;
> };
> 
> #define FITRIM          _IOWR('X', 121, struct fstrim_range)
> 
> int main(int argc, char **argv)
> {
>         struct fstrim_range range;
>         uint64_t len;
>         int fd;
> 
>         if (argc < 2) {
>                 fprintf(stderr, "usage: %s mountpoint [size]\n", argv[0]);
>                 return 1;
>         }
> 
>         if (argc == 3)
>                 len = atoll(argv[1]);
>         else
>                 len = ((1UL<<31) - 1);
> 
>         range.start = 0;
>         range.len = len;
>         range.minlen = 256 * 1024;      /* Minimum is 256KiB */

Why exactly you need to set this ? What will happen if the minlen is 0 ?

> 
>         fd = open(argv[1], O_RDONLY);
>         if (fd < 0) {
>                 perror("open");
>                 return 1;
>         }
> 
>         if (ioctl(fd, FITRIM, &range)) {
>                 if (errno == EOPNOTSUPP)
>                         fprintf(stderr, "TRIM not supported\n");
>                 else
>                         perror("FITRIM");
>                 return 1;
>         }
> 
>         fprintf(stderr, "Trimmed size %llu\n", range.len);
> 
>         return 0;
> }
> 
> >
> > Thanks!
> > -Lukas
> >
> >>
> >> Signed-off-by: Kyungmin Park <kyungmin.park@xxxxxxxxxxx>
> >> ---
> >> Changelog v3:
> >>       Adjust the minlen from queue discard_granularity
> >>       Use the corrent len usage
> >> Changelog v2:
> >>       Use the given start and len as Lukas comments
> >>       Check the queue supports discard feature
> >> ---
> >> diff --git a/fs/fat/fat.h b/fs/fat/fat.h
> >> index f504089..08b53e1 100644
> >> --- a/fs/fat/fat.h
> >> +++ b/fs/fat/fat.h
> >> @@ -299,6 +299,7 @@ extern int fat_alloc_clusters(struct inode *inode, int *cluster,
> >>                             int nr_cluster);
> >>  extern int fat_free_clusters(struct inode *inode, int cluster);
> >>  extern int fat_count_free_clusters(struct super_block *sb);
> >> +extern int fat_trim_fs(struct super_block *sb, struct fstrim_range *range);
> >>
> >>  /* fat/file.c */
> >>  extern long fat_generic_ioctl(struct file *filp, unsigned int cmd,
> >> diff --git a/fs/fat/fatent.c b/fs/fat/fatent.c
> >> index b47d2c9..a8e3837 100644
> >> --- a/fs/fat/fatent.c
> >> +++ b/fs/fat/fatent.c
> >> @@ -1,6 +1,8 @@
> >>  /*
> >>   * Copyright (C) 2004, OGAWA Hirofumi
> >>   * Released under GPL v2.
> >> + *
> >> + * Batched discard support by Kyungmin Park <kyungmin.park@xxxxxxxxxxx>
> >>   */
> >>
> >>  #include <linux/module.h>
> >> @@ -541,6 +543,16 @@ out:
> >>       return err;
> >>  }
> >>
> >> +static int fat_issue_discard(struct super_block *sb, int cluster, int nr_clus)
> >> +{
> >> +     struct msdos_sb_info *sbi = MSDOS_SB(sb);
> >> +     sector_t block, nr_blocks;
> >> +
> >> +     block = fat_clus_to_blknr(sbi, cluster);
> >> +     nr_blocks = nr_clus * sbi->sec_per_clus;
> >> +     return sb_issue_discard(sb, block, nr_blocks, GFP_NOFS, 0);
> >> +}
> >> +
> >>  int fat_free_clusters(struct inode *inode, int cluster)
> >>  {
> >>       struct super_block *sb = inode->i_sb;
> >> @@ -575,11 +587,7 @@ int fat_free_clusters(struct inode *inode, int cluster)
> >>                       if (cluster != fatent.entry + 1) {
> >>                               int nr_clus = fatent.entry - first_cl + 1;
> >>
> >> -                             sb_issue_discard(sb,
> >> -                                     fat_clus_to_blknr(sbi, first_cl),
> >> -                                     nr_clus * sbi->sec_per_clus,
> >> -                                     GFP_NOFS, 0);
> >> -
> >> +                             fat_issue_discard(sb, first_cl, nr_clus);
> >>                               first_cl = cluster;
> >>                       }
> >>               }
> >> @@ -683,3 +691,88 @@ out:
> >>       unlock_fat(sbi);
> >>       return err;
> >>  }
> >> +
> >> +int fat_trim_fs(struct super_block *sb, struct fstrim_range *range)
> >> +{
> >> +     struct msdos_sb_info *sbi = MSDOS_SB(sb);
> >> +     struct fatent_operations *ops = sbi->fatent_ops;
> >> +     struct fat_entry fatent;
> >> +     unsigned long reada_blocks, reada_mask, cur_block;
> >> +     int err = 0, free, count, entry;
> >> +     int start, len, minlen, trimmed;
> >> +
> >> +     start = range->start >> sb->s_blocksize_bits;
> >> +     start = start / sbi->sec_per_clus;
> >> +     len = range->len >> sb->s_blocksize_bits;
> >> +     len = len / sbi->sec_per_clus;
> >> +     minlen = range->minlen >> sb->s_blocksize_bits;
> >> +     minlen = minlen / sbi->sec_per_clus;
> >> +     trimmed = 0;
> >> +     count = 0;
> >> +
> >> +     lock_fat(sbi);
> >> +     if (sbi->free_clusters != -1 && sbi->free_clus_valid)
> >> +             goto out;
> >> +
> >> +     reada_blocks = FAT_READA_SIZE >> sb->s_blocksize_bits;
> >> +     reada_mask = reada_blocks - 1;
> >> +     cur_block = 0;
> >> +
> >> +     entry = 0;
> >> +     free = 0;
> >> +     fatent_init(&fatent);
> >> +
> >> +     if (start < FAT_START_ENT)
> >> +             start = FAT_START_ENT;
> >> +
> >> +     fatent_set_entry(&fatent, start);
> >> +
> >> +     while (count < sbi->max_cluster) {
> >> +             if (fatent.entry >= sbi->max_cluster)
> >> +                     fatent.entry = FAT_START_ENT;
> >> +             /* readahead of fat blocks */
> >> +             if ((cur_block & reada_mask) == 0) {
> >> +                     unsigned long rest = sbi->fat_length - cur_block;
> >> +                     fat_ent_reada(sb, &fatent, min(reada_blocks, rest));
> >
> > You really do not need new variable "rest" just for passing it into one
> > function. Get rid of it.
> 
> Umm. I don't want to modify it since it's routine is same as
> free_count codes. I just borrowed it from FAT codes.
> >
> >> +             }
> >> +             cur_block++;
> >> +
> >> +             err = fat_ent_read_block(sb, &fatent);
> >> +             if (err)
> >> +                     goto out;
> >> +
> >> +             do {
> >> +                     if (ops->ent_get(&fatent) == FAT_ENT_FREE) {
> >> +                             free++;
> >> +                             if (!entry)
> >> +                                     entry = fatent.entry;
> >> +                             if (count >= len && free >= minlen) {
> >> +                                     fat_issue_discard(sb, entry, free);
> >> +                                     trimmed += free;

I think you can remove this condition completely is you move "done"
label befor the if (free >= minlen) condition.

> > I really do not understand FAT code very much, but is this right ?
> > Should not you be setting free = 0 ?
> Right but count is larger then "len". it will exit at next if (count
> >= len) goto done statement.

Oh, ok I see. But it proves my point that this code is not very well
readable.

> 
> > What will happen if you'll end up
> > in the same branch in next iteration ? -- free will be still set to
> > previous value+1, bu you'll be discarding next entry. I am sorry but
> > this whole thing is not very readable.
> 
> >
> >> +                             }
> >> +                             if (count >= len)
> >> +                                     goto done;
				   ^^^^^^^^^^^^^^^^^^
this

> >> +                     } else if (entry) {
> >> +                             if (free >= minlen) {
> >> +                                     fat_issue_discard(sb, entry, free);
> >> +                                     trimmed += free;
> >> +                             }
> >> +                             if (count >= len)
> >> +                                     goto done;
				   ^^^^^^^^^^^^^^^^^^
and this

> >> +                             free = 0;
> >> +                             entry = 0;
> >> +                     }
> >
> > I don't not see why you are testing count all the time since it has not been
> > changed since the "if" condition started. how about doing one test
> > before the "if" condition ?
> 
> For looping the whole fat max_cluster size. now start can be any
> address and if start is a middle point and len is max, then it will
> search from middle -> end -> start -> middle. The "count" is used for
> this purpose.
> 
> Thank you,
> Kyungmin Park
> >
can go here -->>
                           if (count >= len)
                                   goto done;

> >> +                     count++;
> >> +             } while (fat_ent_next(sbi, &fatent));
> >> +     }
> >> +     if (free >= minlen) {
> >> +             fat_issue_discard(sb, entry, free);
> >> +             trimmed += free;
> >> +     }
> >> +done:
> >> +     range->len = (trimmed * sbi->sec_per_clus) << sb->s_blocksize_bits;
> >> +     fatent_brelse(&fatent);
> >> +out:
> >> +     unlock_fat(sbi);
> >> +     return err;
> >> +}
> >> diff --git a/fs/fat/file.c b/fs/fat/file.c
> >> index 7257752..9910aba 100644
> >> --- a/fs/fat/file.c
> >> +++ b/fs/fat/file.c
> >> @@ -125,6 +125,36 @@ long fat_generic_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
> >>               return fat_ioctl_get_attributes(inode, user_attr);
> >>       case FAT_IOCTL_SET_ATTRIBUTES:
> >>               return fat_ioctl_set_attributes(filp, user_attr);
> >> +     case FITRIM:
> >> +     {
> >> +             struct super_block *sb = inode->i_sb;
> >> +             struct request_queue *q = bdev_get_queue(sb->s_bdev);
> >> +             struct fstrim_range range;
> >> +             int ret = 0;
> >> +
> >> +             if (!capable(CAP_SYS_ADMIN))
> >> +                     return -EPERM;
> >> +
> >> +             if (!blk_queue_discard(q))
> >> +                     return -EOPNOTSUPP;
> >> +
> >> +             if (copy_from_user(&range, (struct fstrim_range *)arg,
> >> +                                     sizeof(range)))
> >> +                     return -EFAULT;
> >> +
> >> +             range.minlen = max((unsigned int)range.minlen,
> >> +                                     q->limits.discard_granularity);
> >> +             ret = fat_trim_fs(sb, &range);
> >> +             if (ret < 0)
> >> +                     return ret;
> >> +
> >> +             if (copy_to_user((struct fstrim_range *)arg, &range,
> >> +                                     sizeof(range)))
> >> +                     return -EFAULT;
> >> +
> >> +             return 0;
> >> +     }
> >> +
> >>       default:
> >>               return -ENOTTY; /* Inappropriate ioctl for device */
> >>       }
> >>
> >
> > --
> >
> 

-- 

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