linux-ext4 - Re: [PATCH v2] ext4:Teach ext4_ext_split to caculate extents efficiently.

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Date:	Wed, 25 May 2011 10:02:37 +0800
From:	Yongqiang Yang <xiaoqiangnk@...il.com>
To:	"Ted Ts'o" <tytso@....edu>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: [PATCH v2] ext4:Teach ext4_ext_split to caculate extents efficiently.

On Wed, May 25, 2011 at 5:07 AM, Ted Ts'o <tytso@....edu> wrote:
> On Mon, May 23, 2011 at 05:30:57PM +0800, Yongqiang Yang wrote:
>> @@ -982,20 +997,13 @@ static int ext4_ext_split(handle_t *handle, struct inode *inode,
>>                       err = -EIO;
>>                       goto cleanup;
>>               }
>> -             while (path[i].p_idx <= EXT_MAX_INDEX(path[i].p_hdr)) {
>> -                     ext_debug("%d: move %d:%llu in new index %llu\n", i,
>> -                                     le32_to_cpu(path[i].p_idx->ei_block),
>> -                                     ext4_idx_pblock(path[i].p_idx),
>> -                                     newblock);
>> -                     /*memmove(++fidx, path[i].p_idx++,
>> -                                     sizeof(struct ext4_extent_idx));
>> -                     neh->eh_entries++;
>> -                     BUG_ON(neh->eh_entries > neh->eh_max);*/
>> -                     path[i].p_idx++;
>> -                     m++;
>> -             }
>> +             /* start copy indexes */
>> +             m = EXT_MAX_INDEX(path[i].p_hdr) - path[i].p_idx++;
>> +             ext_debug("cur 0x%p, last 0x%p\n", path[i].p_idx,
>> +                             EXT_MAX_INDEX(path[i].p_hdr));
>> +             ext4_ext_show_move(inode, path, newblock, i);
>>               if (m) {
>> -                     memmove(++fidx, path[i].p_idx - m,
>> +                     memmove(++fidx, path[i].p_idx,
>>                               sizeof(struct ext4_extent_idx) * m);
>>                       le16_add_cpu(&neh->eh_entries, m);
>>               }
>
Hi Ted,

Thank you for your review.  I had looked at this case.

> So the old code mutates path[i].p_idx, where as your new code doesn't.
path[i]p_idx is mutated to EXT_MAX_INDEX(path[i].p_hdr) + 1, it is
meaningless.  ext4_ext_split() is used only by
ext4_ext_create_new_leaf() which drops the path after ext4_ext_split()
returns, so the path[i].p_idx is no longer used.

> The one thing that scares me is that ext4_ext_insert_index() is passed
> &path[at], the function preferences path[at].p_idx.
ext4_ext_split() insert k indexes, where k = depth - at -1, starting
from depth - 1 to depth - 1 - k + 1 = depth - k = at + 1.

So old code does not mutate depth[at].p_idx.

I had tested the patch with fsx.  I am not sure if this test is
enough.  If you want more tests, I can do it.

Thanks,
Yongqiang.
>
> Have you looked at this case?
>
>                                        - Ted
>



-- 
Best Wishes
Yongqiang Yang
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