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authorJaegeuk Kim <jaegeuk.kim@samsung.com>2014-02-27 13:20:00 +0400
committerJaegeuk Kim <jaegeuk.kim@samsung.com>2014-02-27 14:56:09 +0400
commit3843154598a00408f4214a68bd536fdf27b1df10 (patch)
treee4e89b1bc769996bf72851baffd62194d9a48385 /Documentation/filesystems/f2fs.txt
parent5d0c667121bfc8be76d1580f485bddbe73465d1a (diff)
downloadlinux-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.txt6
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