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Date: Fri, 15 Apr 2011 09:12:13 +0800
From: Yongqiang Yang <xiaoqiangnk@...il.com>
To: Mingming Cao <cmm@...ibm.com>
Cc: linux-ext4@...r.kernel.org, achender@...ux.vnet.ibm.com
Subject: Re: [PATCH RFC 1/3] ext4:Add a function merging extent right and left.
On Fri, Apr 15, 2011 at 3:03 AM, Mingming Cao <cmm@...ibm.com> wrote:
> On Wed, 2011-04-13 at 22:40 -0700, Yongqiang Yang wrote:
>> 1] Rename ext4_ext_try_to_merge() to ext4_ext_try_to_merge_right().
>>
>> 2] Add a new function ext4_ext_try_to_merge() which tries to merge
>> an extent both left and right.
>>
>> 3] Use the new function in ext4_ext_convert_unwritten_endio() and
>> ext4_ext_insert_extent().
>>
>> Signed-off-by: Yongqiang Yang <xiaoqiangnk@...il.com>
>> ---
>> fs/ext4/extents.c | 65 ++++++++++++++++++++++++++++------------------------
>> 1 files changed, 35 insertions(+), 30 deletions(-)
>>
>> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
>> index dd2cb50..11f30d2 100644
>> --- a/fs/ext4/extents.c
>> +++ b/fs/ext4/extents.c
>> @@ -1563,7 +1563,7 @@ ext4_can_extents_be_merged(struct inode *inode, struct ext4_extent *ex1,
>> * Returns 0 if the extents (ex and ex+1) were _not_ merged and returns
>> * 1 if they got merged.
>> */
>> -static int ext4_ext_try_to_merge(struct inode *inode,
>> +static int ext4_ext_try_to_merge_right(struct inode *inode,
>> struct ext4_ext_path *path,
>> struct ext4_extent *ex)
>> {
>> @@ -1603,6 +1603,31 @@ static int ext4_ext_try_to_merge(struct inode *inode,
>> }
>>
>> /*
>> + * This function tries to merge the @ex extent to neighbours in the tree.
>> + * return 1 if merge left else 0.
>> + */
>> +static int ext4_ext_try_to_merge(struct inode *inode,
>> + struct ext4_ext_path *path,
>> + struct ext4_extent *ex) {
>> + struct ext4_extent_header *eh;
>> + unsigned int depth;
>> + int merge_done = 0;
>> + int ret = 0;
>> +
>> + depth = ext_depth(inode);
>> + BUG_ON(path[depth].p_hdr == NULL);
>> + eh = path[depth].p_hdr;
>> +
>> + if (ex > EXT_FIRST_EXTENT(eh))
>> + merge_done = ext4_ext_try_to_merge_right(inode, path, ex - 1);
>> +
>> + if (!merge_done)
>> + ret = ext4_ext_try_to_merge_right(inode, path, ex);
>> +
>
> Is there any reason not to merge right after merge left? The old code
> does both, I think.
What does merge left do? Actually it does as merge right, it merge
ex-1 to right until no more merges can be done. So if merge to right
happens then, ex,ex+1 has been tried to merge also.
>
>> + return ret;
>> +}
>> +
>> +/*
>> * check if a portion of the "newext" extent overlaps with an
>> * existing extent.
>> *
>> @@ -3039,6 +3064,7 @@ fix_extent_len:
>> ext4_ext_dirty(handle, inode, path + depth);
>> return err;
>> }
>> +
>> static int ext4_convert_unwritten_extents_endio(handle_t *handle,
>> struct inode *inode,
>> struct ext4_ext_path *path)
>> @@ -3047,46 +3073,25 @@ static int ext4_convert_unwritten_extents_endio(handle_t *handle,
>> struct ext4_extent_header *eh;
>> int depth;
>> int err = 0;
>> - int ret = 0;
>>
>> depth = ext_depth(inode);
>> eh = path[depth].p_hdr;
>> ex = path[depth].p_ext;
>>
>> + ext_debug("ext4_convert_unwritten_extents_endio: inode %lu, logical"
>> + "block %llu, max_blocks %u\n", inode->i_ino,
>> + (unsigned long long)le32_to_cpu(ex->ee_block),
>> + ext4_ext_get_actual_len(ex));
>> +
>> err = ext4_ext_get_access(handle, inode, path + depth);
>> if (err)
>> goto out;
>> /* first mark the extent as initialized */
>> ext4_ext_mark_initialized(ex);
>>
>> - /*
>> - * We have to see if it can be merged with the extent
>> - * on the left.
>> - */
>> - if (ex > EXT_FIRST_EXTENT(eh)) {
>> - /*
>> - * To merge left, pass "ex - 1" to try_to_merge(),
>> - * since it merges towards right _only_.
>> - */
>> - ret = ext4_ext_try_to_merge(inode, path, ex - 1);
>> - if (ret) {
>> - err = ext4_ext_correct_indexes(handle, inode, path);
>> - if (err)
>> - goto out;
>> - depth = ext_depth(inode);
>> - ex--;
>> - }
>> - }
>> - /*
>> - * Try to Merge towards right.
>> - */
>> - ret = ext4_ext_try_to_merge(inode, path, ex);
>> - if (ret) {
>> - err = ext4_ext_correct_indexes(handle, inode, path);
>> - if (err)
>> - goto out;
>> - depth = ext_depth(inode);
>> - }
>> + /* correct indexes is nt needed becasue borders are not changed */
>> + ext4_ext_try_to_merge(inode, path, ex);
>> +
>
> Ah, so you discovered an issue -- currently ext4 can't merge across the
> index block borders. that's a pity. This might need to fix up,
Yes, currently borders are changed only in one case that storing an
extent to an empty leaf.
I think the patch which enable merging across index block should be
independent on these patches.
> especially with split is going to be heavily used in punch hole,
> snapshots, direct IO handling holes.
What does direct IO here refer to? It seems I am missing something.
These patches involves ext4_ext_convrt_to_initialized() in buffer
write case, and split_unwritten_extents() and
convert_to_initialized_endio() in direct IO case.
>
>
>> /* Mark modified extent as dirty */
>> err = ext4_ext_dirty(handle, inode, path + depth);
>> out:
>
>
>
--
Best Wishes
Yongqiang Yang
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