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Advance move_blocks extent search offset

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The move_blocks ioctl finds extents to move in the source file by
searching from the starting block offset of the region to move.
Logically, this is fine.  After each extent item is deleted the next
search will find the next extent.

The problem is that deleted items still exist in the item cache.  The
next iteration has to skip over all the deleted extents from the start
of the region.  This is fine with large extents, but with heavily
fragmented extents this creates a huge amplification of the number of
items to traverse when moving the fragmented extents in a large file.
(It's not quite O(n^2)/2 for the total extents, deleted items are purged
as we write out the dirty items in each transaction.. but it's still
immense.)

The fix is to simply start searching for the next extent after the one
we just moved.

Signed-off-by: Zach Brown <zab@versity.com>
This commit is contained in:
Zach Brown
2023-06-28 16:47:41 -07:00
parent 564b942ead
commit 847916860d
1 changed files with 8 additions and 1 deletions
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9
kmod/src/data.c
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@@ -1267,6 +1267,7 @@ int scoutfs_data_move_blocks(struct inode *from, u64 from_off,
from_iblock = from_off >> SCOUTFS_BLOCK_SM_SHIFT;
count = (byte_len + SCOUTFS_BLOCK_SM_MASK) >> SCOUTFS_BLOCK_SM_SHIFT;
to_iblock = to_off >> SCOUTFS_BLOCK_SM_SHIFT;
from_start = from_iblock;
/* only move extent blocks inside i_size, careful not to wrap */
from_size = i_size_read(from);
@@ -1343,7 +1344,7 @@ int scoutfs_data_move_blocks(struct inode *from, u64 from_off,
/* find the next extent to move */
ret = scoutfs_ext_next(sb, &data_ext_ops, &from_args,
from_iblock, 1, &ext);
from_start, 1, &ext);
if (ret < 0) {
if (ret == -ENOENT) {
done = true;
@@ -1431,6 +1432,12 @@ int scoutfs_data_move_blocks(struct inode *from, u64 from_off,
i_size_read(from);
i_size_write(to, to_size);
}
/* find next after moved extent, avoiding wrapping */
if (from_start + len < from_start)
from_start = from_iblock + count + 1;
else
from_start += len;
}