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Date: Fri, 25 Feb 2011 12:17:12 +0100 (CET)
From: Lukas Czerner <lczerner@...hat.com>
To: Kyungmin Park <kmpark@...radead.org>
cc: OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>,
linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
Lukas Czerner <lczerner@...hat.com>
Subject: Re: [PATCH v3] fat: Batched discard support for fat
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.
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.
> + }
> + 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 really do not understand FAT code very much, but is this right ?
Should not you be setting free = 0 ? 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;
> + } else if (entry) {
> + if (free >= minlen) {
> + fat_issue_discard(sb, entry, free);
> + trimmed += free;
> + }
> + if (count >= len)
> + goto done;
> + 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 ?
> + 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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