On Wed, Aug 27, 2014 at 9:19 AM, Liu Bo <bo.li.liu@xxxxxxxxxx> wrote:
> On Fri, May 30, 2014 at 03:16:10PM +0800, Qu Wenruo wrote:
>> btrfs_punch_hole() will truncate unaligned pages or punch hole on a
>> already existed hole.
>> This will cause unneeded zero page or holes splitting the original huge
>> hole.
>>
>> This patch will skip already existed holes before any page truncating or
>> hole punching.
>>
>> Signed-off-by: Qu Wenruo <quwenruo@xxxxxxxxxxxxxx>
>> ---
>> fs/btrfs/file.c | 112 +++++++++++++++++++++++++++++++++++++++++++++++++-------
>> 1 file changed, 98 insertions(+), 14 deletions(-)
>>
>> diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
>> index ae6af07..93915d1 100644
>> --- a/fs/btrfs/file.c
>> +++ b/fs/btrfs/file.c
>> @@ -2168,6 +2168,37 @@ out:
>> return 0;
>> }
>>
>> +/*
>> + * Find a hole extent on given inode and change start/len to the end of hole
>> + * extent.(hole/vacuum extent whose em->start <= start &&
>> + * em->start + em->len > start)
>> + * When a hole extent is found, return 1 and modify start/len.
>> + */
>> +static int find_first_non_hole(struct inode *inode, u64 *start, u64 *len)
>> +{
>> + struct extent_map *em;
>> + int ret = 0;
>> +
>> + em = btrfs_get_extent(inode, NULL, 0, *start, *len, 0);
>> + if (IS_ERR_OR_NULL(em)) {
>> + if (!em)
>> + ret = -ENOMEM;
>> + else
>> + ret = PTR_ERR(em);
>> + return ret;
>> + }
>> +
>> + /* Hole or vacuum extent(only exists in no-hole mode) */
>> + if (em->block_start == EXTENT_MAP_HOLE) {
>> + ret = 1;
>> + *len = em->start + em->len > *start + *len ?
>> + 0 : *start + *len - em->start - em->len;
>> + *start = em->start + em->len;
>> + }
>> + free_extent_map(em);
>> + return ret;
>> +}
>> +
>> static int btrfs_punch_hole(struct inode *inode, loff_t offset, loff_t len)
>> {
>> struct btrfs_root *root = BTRFS_I(inode)->root;
>> @@ -2175,17 +2206,18 @@ static int btrfs_punch_hole(struct inode *inode, loff_t offset, loff_t len)
>> struct btrfs_path *path;
>> struct btrfs_block_rsv *rsv;
>> struct btrfs_trans_handle *trans;
>> - u64 lockstart = round_up(offset, BTRFS_I(inode)->root->sectorsize);
>> - u64 lockend = round_down(offset + len,
>> - BTRFS_I(inode)->root->sectorsize) - 1;
>> - u64 cur_offset = lockstart;
>> + u64 lockstart;
>> + u64 lockend;
>> + u64 tail_start;
>> + u64 tail_len;
>> + u64 orig_start = offset;
>> + u64 cur_offset;
>> u64 min_size = btrfs_calc_trunc_metadata_size(root, 1);
>> u64 drop_end;
>> int ret = 0;
>> int err = 0;
>> int rsv_count;
>> - bool same_page = ((offset >> PAGE_CACHE_SHIFT) ==
>> - ((offset + len - 1) >> PAGE_CACHE_SHIFT));
>> + bool same_page;
>> bool no_holes = btrfs_fs_incompat(root->fs_info, NO_HOLES);
>> u64 ino_size = round_up(inode->i_size, PAGE_CACHE_SIZE);
>>
>> @@ -2194,6 +2226,21 @@ static int btrfs_punch_hole(struct inode *inode, loff_t offset, loff_t len)
>> return ret;
>>
>> mutex_lock(&inode->i_mutex);
>> + ret = find_first_non_hole(inode, &offset, &len);
>> + if (ret < 0)
>> + goto out_only_mutex;
>> + if (ret && !len) {
>> + /* Already in a large hole */
>> + ret = 0;
>> + goto out_only_mutex;
>> + }
>> +
>> + lockstart = round_up(offset , BTRFS_I(inode)->root->sectorsize);
>> + lockend = round_down(offset + len,
>> + BTRFS_I(inode)->root->sectorsize) - 1;
>
> Why do we round_up lockstart but round_down lockend?
>
> For [0,4095], then lockstart is 4096 and lockend is (u64)-1, any thoughts?
Seems odd, but is it a problem for that case?
The same_page check below makes us return without locking the range in
the iotree using the computed values for lockstart and lockend.
>
> thanks,
> -liubo
>
>> + same_page = ((offset >> PAGE_CACHE_SHIFT) ==
>> + ((offset + len - 1) >> PAGE_CACHE_SHIFT));
>> +
>> /*
>> * We needn't truncate any page which is beyond the end of the file
>> * because we are sure there is no data there.
>> @@ -2205,8 +2252,7 @@ static int btrfs_punch_hole(struct inode *inode, loff_t offset, loff_t len)
>> if (same_page && len < PAGE_CACHE_SIZE) {
>> if (offset < ino_size)
>> ret = btrfs_truncate_page(inode, offset, len, 0);
>> - mutex_unlock(&inode->i_mutex);
>> - return ret;
>> + goto out_only_mutex;
>> }
>>
>> /* zero back part of the first page */
>> @@ -2218,12 +2264,39 @@ static int btrfs_punch_hole(struct inode *inode, loff_t offset, loff_t len)
>> }
>> }
>>
>> - /* zero the front end of the last page */
>> - if (offset + len < ino_size) {
>> - ret = btrfs_truncate_page(inode, offset + len, 0, 1);
>> - if (ret) {
>> - mutex_unlock(&inode->i_mutex);
>> - return ret;
>> + /* Check the aligned pages after the first unaligned page,
>> + * if offset != orig_start, which means the first unaligned page
>> + * including serveral following pages are already in holes,
>> + * the extra check can be skipped */
>> + if (offset == orig_start) {
>> + /* after truncate page, check hole again */
>> + len = offset + len - lockstart;
>> + offset = lockstart;
>> + ret = find_first_non_hole(inode, &offset, &len);
>> + if (ret < 0)
>> + goto out_only_mutex;
>> + if (ret && !len) {
>> + ret = 0;
>> + goto out_only_mutex;
>> + }
>> + lockstart = offset;
>> + }
>> +
>> + /* Check the tail unaligned part is in a hole */
>> + tail_start = lockend + 1;
>> + tail_len = offset + len - tail_start;
>> + if (tail_len) {
>> + ret = find_first_non_hole(inode, &tail_start, &tail_len);
>> + if (unlikely(ret < 0))
>> + goto out_only_mutex;
>> + if (!ret) {
>> + /* zero the front end of the last page */
>> + if (tail_start + tail_len < ino_size) {
>> + ret = btrfs_truncate_page(inode,
>> + tail_start + tail_len, 0, 1);
>> + if (ret)
>> + goto out_only_mutex;
>> + }
>> }
>> }
>>
>> @@ -2299,6 +2372,8 @@ static int btrfs_punch_hole(struct inode *inode, loff_t offset, loff_t len)
>> BUG_ON(ret);
>> trans->block_rsv = rsv;
>>
>> + cur_offset = lockstart;
>> + len = lockend - cur_offset;
>> while (cur_offset < lockend) {
>> ret = __btrfs_drop_extents(trans, root, inode, path,
>> cur_offset, lockend + 1,
>> @@ -2339,6 +2414,14 @@ static int btrfs_punch_hole(struct inode *inode, loff_t offset, loff_t len)
>> rsv, min_size);
>> BUG_ON(ret); /* shouldn't happen */
>> trans->block_rsv = rsv;
>> +
>> + ret = find_first_non_hole(inode, &cur_offset, &len);
>> + if (unlikely(ret < 0))
>> + break;
>> + if (ret && !len) {
>> + ret = 0;
>> + break;
>> + }
>> }
>>
>> if (ret) {
>> @@ -2372,6 +2455,7 @@ out_free:
>> out:
>> unlock_extent_cached(&BTRFS_I(inode)->io_tree, lockstart, lockend,
>> &cached_state, GFP_NOFS);
>> +out_only_mutex:
>> mutex_unlock(&inode->i_mutex);
>> if (ret && !err)
>> err = ret;
>> --
>> 1.9.3
>>
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--
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Unreasonable men adapt the world to themselves.
That's why all progress depends on unreasonable men."
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