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Date: Thu, 24 Feb 2011 19:17:53 +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 v2] fat: Batched discard support for fat
On Thu, Feb 24, 2011 at 5:53 PM, Lukas Czerner <lczerner@...hat.com> wrote:
> On Thu, 24 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/
>>
>> Signed-off-by: Kyungmin Park <kyungmin.park@...sung.com>
>
> Hi Kyungmin,
> thanks to second version. How did you test it ? You can try xtestest
> 251 for simple verification.
> I can not really comment on FAT specific code, however I have couple of
> comments bellow.
>
> Thanks!
> -Lukas
>
>> ---
>> 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..ea31ee4 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);
> ^^^^^^^^
> This patch does not pass checkpatch.pl script. Use tabs for indention.
right, I will fix it. now passed the checkpatch.pl.
>
>> +}
>> +
>> 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;
>
> I should have mention that earlier, but you can also adjust mineln
> according to the discard_granularity, because extents smaller than that
> would not be discarded anyway.
I adjust the minlen granularity with fat cluster unit. and FAT don't
know what's the effected block size. it's role of user side.
>
>> + 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;
>
> You're not using start anywhere.
>
>> +
>> + fatent_set_entry(&fatent, FAT_START_ENT);
It should be 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));
>> + }
>> + 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 (free >= (len - trimmed) && free >= minlen) {
>
> It seems to me that you are using len as number of bytes to trim. This
> is not right and I am sorry for not explaining it correctly. "len" is
> supposed to be a number of bytes you want to "investigate" from the start.
> So it means that you will trim every single free extent bigger than minlen
> between "start" byte and "start + len" byte of the underlying device, or
> partition.
No. len is adjusted at fat cluster number. it's not used byte unit.
I think it's easy to compare with fat internal units.
I hope fat peoples comment this one.
Thank you,
Kyungmin Park
>
>> + fat_issue_discard(sb, entry, free);
>> + trimmed += free;
>> + }
>> + if (trimmed >= len)
>> + goto done;
>> + } else if (entry) {
>> + if (free >= minlen) {
>> + fat_issue_discard(sb, entry, free);
>> + trimmed += free;
>> + }
>> + if (trimmed >= len)
>> + goto done;
>> + free = 0;
>> + entry = 0;
>> + }
>> + 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..05e6545 100644
>> --- a/fs/fat/file.c
>> +++ b/fs/fat/file.c
>> @@ -125,6 +125,34 @@ 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;
>> +
>> + 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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