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| author | Jaegeuk Kim <jaegeuk.kim@samsung.com> | 2014-02-27 13:20:00 +0400 |
|---|---|---|
| committer | Jaegeuk Kim <jaegeuk.kim@samsung.com> | 2014-02-27 14:56:09 +0400 |
| commit | 3843154598a00408f4214a68bd536fdf27b1df10 (patch) | |
| tree | e4e89b1bc769996bf72851baffd62194d9a48385 /Documentation/filesystems/f2fs.txt | |
| parent | 5d0c667121bfc8be76d1580f485bddbe73465d1a (diff) | |
| download | linux-3843154598a00408f4214a68bd536fdf27b1df10.tar.xz | |
f2fs: introduce large directory support
This patch introduces an i_dir_level field to support large directory.
Previously, f2fs maintains multi-level hash tables to find a dentry quickly
from a bunch of chiild dentries in a directory, and the hash tables consist of
the following tree structure as below.
In Documentation/filesystems/f2fs.txt,
----------------------
A : bucket
B : block
N : MAX_DIR_HASH_DEPTH
----------------------
level #0 | A(2B)
|
level #1 | A(2B) - A(2B)
|
level #2 | A(2B) - A(2B) - A(2B) - A(2B)
. | . . . .
level #N/2 | A(2B) - A(2B) - A(2B) - A(2B) - A(2B) - ... - A(2B)
. | . . . .
level #N | A(4B) - A(4B) - A(4B) - A(4B) - A(4B) - ... - A(4B)
But, if we can guess that a directory will handle a number of child files,
we don't need to traverse the tree from level #0 to #N all the time.
Since the lower level tables contain relatively small number of dentries,
the miss ratio of the target dentry is likely to be high.
In order to avoid that, we can configure the hash tables sparsely from level #0
like this.
level #0 | A(2B) - A(2B) - A(2B) - A(2B)
level #1 | A(2B) - A(2B) - A(2B) - A(2B) - A(2B) - ... - A(2B)
. | . . . .
level #N/2 | A(2B) - A(2B) - A(2B) - A(2B) - A(2B) - ... - A(2B)
. | . . . .
level #N | A(4B) - A(4B) - A(4B) - A(4B) - A(4B) - ... - A(4B)
With this structure, we can skip the ineffective tree searches in lower level
hash tables.
This patch adds just a facility for this by introducing i_dir_level in
f2fs_inode.
Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>
Diffstat (limited to 'Documentation/filesystems/f2fs.txt')
| -rw-r--r-- | Documentation/filesystems/f2fs.txt | 6 |
1 files changed, 4 insertions, 2 deletions
diff --git a/Documentation/filesystems/f2fs.txt b/Documentation/filesystems/f2fs.txt index b8d284975f0f..8eb06b0a7d2b 100644 --- a/Documentation/filesystems/f2fs.txt +++ b/Documentation/filesystems/f2fs.txt @@ -444,9 +444,11 @@ The number of blocks and buckets are determined by, # of blocks in level #n = | `- 4, Otherwise - ,- 2^n, if n < MAX_DIR_HASH_DEPTH / 2, + ,- 2^ (n + dir_level), + | if n < MAX_DIR_HASH_DEPTH / 2, # of buckets in level #n = | - `- 2^((MAX_DIR_HASH_DEPTH / 2) - 1), Otherwise + `- 2^((MAX_DIR_HASH_DEPTH / 2 + dir_level) - 1), + Otherwise When F2FS finds a file name in a directory, at first a hash value of the file name is calculated. Then, F2FS scans the hash table in level #0 to find the |