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authorTheodore Ts'o <tytso@mit.edu>2012-08-17 09:48:17 -0400
committerTheodore Ts'o <tytso@mit.edu>2012-08-17 09:48:17 -0400
commitdf981d03eeff7971ac7e6ff37000bfa702327ef1 (patch)
tree4e944139b9e45c4af910c517b57f2d9bc7c81a1a /Documentation
parent01fc48e8929e45e67527200017cff4e74e4ba054 (diff)
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ext4: add max_dir_size_kb mount option
Very large directories can cause significant performance problems, or perhaps even invoke the OOM killer, if the process is running in a highly constrained memory environment (whether it is VM's with a small amount of memory or in a small memory cgroup). So it is useful, in cloud server/data center environments, to be able to set a filesystem-wide cap on the maximum size of a directory, to ensure that directories never get larger than a sane size. We do this via a new mount option, max_dir_size_kb. If there is an attempt to grow the directory larger than max_dir_size_kb, the system call will return ENOSPC instead. Google-Bug-Id: 6863013 Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/filesystems/ext4.txt10
1 files changed, 10 insertions, 0 deletions
diff --git a/Documentation/filesystems/ext4.txt b/Documentation/filesystems/ext4.txt
index 1b7f9ac..104322b 100644
--- a/Documentation/filesystems/ext4.txt
+++ b/Documentation/filesystems/ext4.txt
@@ -375,6 +375,16 @@ dioread_nolock locking. If the dioread_nolock option is specified
Because of the restrictions this options comprises
it is off by default (e.g. dioread_lock).
+max_dir_size_kb=n This limits the size of directories so that any
+ attempt to expand them beyond the specified
+ limit in kilobytes will cause an ENOSPC error.
+ This is useful in memory constrained
+ environments, where a very large directory can
+ cause severe performance problems or even
+ provoke the Out Of Memory killer. (For example,
+ if there is only 512mb memory available, a 176mb
+ directory may seriously cramp the system's style.)
+
i_version Enable 64-bit inode version support. This option is
off by default.
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