[Ocfs2-devel] [PATCH 1/3] ocfs2: Add ocfs2_trim_fs for SSD trim support.

[Tao Ma]

On 03/08/2011 12:55 PM, Tristan Ye wrote:
> Hi Tao,
> 
>    Most of codes looks pretty neat to me, few comments inlined below:
Thanks for the review.
> 
> Tao Ma wrote:
>> From: Tao Ma <boyu.mt at taobao.com>
>>
>> Add ocfs2_trim_fs to support trimming freed clusters in the
>> volume. A range will be given and all the freed clusters greater
>> than minlen will be discarded to the block layer.
>>
>> Signed-off-by: Tao Ma <boyu.mt at taobao.com>
>> ---
>>  fs/ocfs2/alloc.c |  154
>> ++++++++++++++++++++++++++++++++++++++++++++++++++++++
>>  fs/ocfs2/alloc.h |    1 +
>>  2 files changed, 155 insertions(+), 0 deletions(-)
>>
>> diff --git a/fs/ocfs2/alloc.c b/fs/ocfs2/alloc.c
>> index b27a0d8..6e1b3b5 100644
>> --- a/fs/ocfs2/alloc.c
>> +++ b/fs/ocfs2/alloc.c
>> @@ -29,6 +29,7 @@
>>  #include <linux/highmem.h>
>>  #include <linux/swap.h>
>>  #include <linux/quotaops.h>
>> +#include <linux/blkdev.h>
>>  
>>  #include <cluster/masklog.h>
>>  
>> @@ -7184,3 +7185,156 @@ out_commit:
>>  out:
>>      return ret;
>>  }
>> +
>> +static int ocfs2_trim_extent(struct super_block *sb,
>> +                 struct ocfs2_group_desc *gd,
>> +                 int start, int count)
>> +{
>> +    u64 discard;
>> +
>> +    count = ocfs2_clusters_to_blocks(sb, count);
>> +    discard = le64_to_cpu(gd->bg_blkno) +
>> +            ocfs2_clusters_to_blocks(sb, start);
>> +
>> +    return sb_issue_discard(sb, discard, count, GFP_NOFS, 0);
>> +}
>> +
>> +static int ocfs2_trim_group(struct super_block *sb,
>> +                struct ocfs2_group_desc *gd,
>> +                int start, int max, int minbits)
>> +{
>> +    int ret = 0, count = 0, next;
>> +    void *bitmap = gd->bg_bitmap;
>> +
>> +    while (start < max) {
>> +        start = ocfs2_find_next_zero_bit(bitmap, max, start);
>> +        if (start >= max)
>> +            break;
> 
>    /* What if the 'start' stands within a hole */
> 
>    if (ocfs2_test_bit(...)) {
>       start = ocfs2_find_next_zero_bit(...);
>       if ((start == -1) || (start >= max))
>          break;
>    }
> 
>> +        next = ocfs2_find_next_bit(bitmap, max, start);
>      next = ocfs2_find_next_bit(...);
>    if (next == -1)
>       break;
next will be set to "-1"? sorry, but where do you get it?
> 
>    if (next > max)
>       next = max;
again, ocfs2_find_next_bit will return a value larger than 'max'? I am
afraid not. Otherwise, it will be nonsense to pass a 'max' to it.
>  
>> +
>> +        if ((next - start) >= minbits) {
>> +            ret = ocfs2_trim_extent(sb, gd,
>> +                        start, next - start);
>> +            if (ret < 0) {
>> +                mlog_errno(ret);
>> +                break;
>> +            }
>> +            count += next - start;
>> +        }
>> +        start = next + 1;
>> +
>> +        if (fatal_signal_pending(current)) {
>> +            count = -ERESTARTSYS;
>> +            break;
>> +        }
>> +
>> +        if ((le16_to_cpu(gd->bg_free_bits_count) - count) < minbits)
>> +            break;
>> +    }
>> +
>> +    if (ret < 0)
>> +        count = ret;
>> +
>> +    return count;
>> +}
>> +
>> +int ocfs2_trim_fs(struct super_block *sb, struct fstrim_range *range)
>> +{
>> +    struct ocfs2_super *osb = OCFS2_SB(sb);
>> +    u64 start, len, minlen, trimmed, first_group, last_group, group;
>    why not using u32 start, len, minlen, trimmed;
we may use 64 bit clusters later I guess. And what's more, they will be
set by the user later. and it may overflow. Say the user pass a u64
range->len, it will overflow with range->len >> osb->s_clustersize_bits.
>> +    int ret, cnt, first_bit, last_bit;
>> +    struct buffer_head *main_bm_bh = NULL;
>> +    struct inode *main_bm_inode = NULL;
>> +    struct buffer_head *gd_bh = NULL;
>> +    struct ocfs2_dinode *main_bm;
>> +    struct ocfs2_group_desc *gd = NULL;
>> +
>> +    if (ocfs2_is_hard_readonly(osb) || ocfs2_is_soft_readonly(osb))
>> +        return -EROFS;
>> +
>> +    start = range->start >> osb->s_clustersize_bits;
>> +    len = range->len >> osb->s_clustersize_bits;
>> +    minlen = range->minlen >> osb->s_clustersize_bits;
> 
>    I guess you may want to count two corner clusters which cover the
> 'start' and 'end' bytes,
> so the appropriate way might be:
> 
>    start = range->start >> osb->s_clustersize_bits;
>    len = ocfs2_clusters_for_bytes(osb->sb, range->start  + range->len);
>    len -= start;
No, I don't want that.. Just want to make it the same as what ext4 did.
See ext4_trim_fs for more details.
>  
>> +    trimmed = 0;
>> +
>> +    if (!len || !minlen || minlen >= osb->bitmap_cpg)
>    'minlen == 0' looks acceptable, which means we allowing discarding
> for all size of extents.
> and what's more, 'len == 0' may not be harmful enough to issue a
> 'EINVAL', returning a legal '0'
> to userspace immediately is fine.
Fair enough. I will change it. Thanks.
> 
> 
>> +        return -EINVAL;
>> +
>> +    main_bm_inode = ocfs2_get_system_file_inode(osb,
>> +                            GLOBAL_BITMAP_SYSTEM_INODE,
>> +                            OCFS2_INVALID_SLOT);
>> +    if (!main_bm_inode) {
>> +        ret = -EIO;
>> +        mlog_errno(ret);
>> +        goto out;
>> +    }
>> +
>> +    mutex_lock(&main_bm_inode->i_mutex);
>> +
>> +    ret = ocfs2_inode_lock(main_bm_inode, &main_bm_bh, 0);
>> +    if (ret < 0) {
>> +        mlog_errno(ret);
>> +        goto out_mutex;
>> +    }
>> +    main_bm = (struct ocfs2_dinode *)main_bm_bh->b_data;
>> +
>> +    if (start >= le32_to_cpu(main_bm->i_clusters)) {
>> +        ret = -EINVAL;
>> +        mlog_errno(ret);
>> +        goto out_unlock;
>> +    }
>> +
>> +    if (start + len > le32_to_cpu(main_bm->i_clusters))
>> +        len = le32_to_cpu(main_bm->i_clusters) - start;
>> +
>> +    /* Determine first and last group to examine based on start and
>> len */
>> +    first_group = ocfs2_which_cluster_group(main_bm_inode, start);
>> +    if (first_group == osb->first_cluster_group_blkno)
>> +        first_bit = start;
>> +    else
>> +        first_bit = start - ocfs2_blocks_to_clusters(sb, first_group);
>> +    last_group = ocfs2_which_cluster_group(main_bm_inode, start + len
>> - 1);
>> +    last_bit = osb->bitmap_cpg;
>> +
>> +    for (group = first_group; group <= last_group;) {
>> +        if (first_bit + len >= osb->bitmap_cpg)
>> +            last_bit = osb->bitmap_cpg - first_bit;
> 
>    is 'first_bit' and 'last_bit' both represent a local offset within a
> cluster group?
> just wondering why last_bit wasn't equal to 'osb->bitmap_cpg' in above
> case(I meant the case
> of 'first_bit + len >= osb->bitmap_cpg'
> 
>> +        else
>> +            last_bit = start + len;
> 
>    why above case is not 'last_bit = first_bit + len';
you are right.  Thanks.

Regards,
Tao