linux-kernel - Re: [PATCH v6] fat: Batched discard support for fat

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Date:	Tue, 29 Mar 2011 14:11:35 +0900
From:	Kyungmin Park <kmpark@...radead.org>
To:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
Cc:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	Lukas Czerner <lczerner@...hat.com>
Subject: Re: [PATCH v6] fat: Batched discard support for fat

On Tue, Mar 29, 2011 at 2:04 PM, OGAWA Hirofumi
<hirofumi@...l.parknet.co.jp> wrote:
> Kyungmin Park <kmpark@...radead.org> writes:
>
>> +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, free, count, entry;
>> +     int start, len, minlen, trimmed;
>> +
>> +     start = range->start >> sb->s_blocksize_bits;
>> +     len = range->len >> sb->s_blocksize_bits;
>> +     len = round_down(start + len, sbi->sec_per_clus);
>> +     start = round_up(start, sbi->sec_per_clus);
>> +     minlen = range->minlen >> sb->s_blocksize_bits;
>> +     minlen = round_up(minlen, sbi->sec_per_clus);
>> +     trimmed = 0;
>> +     count = 0;
>> +     err = -EINVAL;
>
> Sorry for didn't mention at previous. You can use ->cluster_size, and
> ->cluster_bits.
>
>> +     if (start >= sbi->max_cluster)
>> +             goto out;
>> +
>> +     len = (len > sbi->max_cluster) ? sbi->max_cluster : len;
>
> [...]
>
>> +             trimmed += free;
>> +     }
>> +     range->len = (u64)(trimmed * sbi->sec_per_clus) << sb->s_blocksize_bits;
>> +     fatent_brelse(&fatent);
>> +out:
>> +     unlock_fat(sbi);
>> +     return err;
>
> Again, this ioctl's design is unclear, and seems to be strange. I
> wouldn't want to add this before clearing it. Please explain what is
> right behavior.

Umm it's out of my scope. it's trim design.
See also btrfs batched discard support. it's also no consideration as
you mentioned.

As I know, now xfs, ext4, and btrfs support this fstrim without these concern.

http://thread.gmane.org/gmane.comp.file-systems.btrfs/9758

Thank you,
Kyungmin Park

>
> E.g. if user specified 0-1024 and FS data block was actually started at
> 2048. What is right behavior? And if the end of blocks, what returned?
> For now, it seems to return range->len == 0 on both cases.
>
> Well, so, my suggestion is providing this like flat one extent
> file. I.e. FS have to map actual block placement to flat. And result
> also like write/read (return bytes as trimed, and at EOF returns 0).
>
> Thanks.
> --
> OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
> --
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