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Date: Wed, 2 Mar 2011 11:07:09 +0900
From: Kyungmin Park <kmpark@...radead.org>
To: Lukas Czerner <lczerner@...hat.com>
Cc: OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>,
linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v3] fat: Batched discard support for fat
On Mon, Feb 28, 2011 at 9:51 PM, Lukas Czerner <lczerner@...hat.com> wrote:
> On Mon, 28 Feb 2011, Kyungmin Park wrote:
>
>> On Fri, Feb 25, 2011 at 8:17 PM, Lukas Czerner <lczerner@...hat.com> wrote:
>> > On Fri, 25 Feb 2011, Kyungmin Park wrote:
>> >
>> >> From: Kyungmin Park <kyungmin.park@...sung.com>
>> >>
>> >> 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 ?
It's dependent on eMMC chip. it's for our environment. If it passed
with 0, the code is working but the less than 256KiB trim command is
meaningless.
>
>>
>> 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@...sung.com>
>> >> ---
>> >> 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@...sung.com>
>> >> */
>> >>
>> >> #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
Okay I will fix it.
>
>> >> + } 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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