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authorTheodore Ts'o <tytso@mit.edu>2015-02-02 00:37:00 -0500
committerAl Viro <viro@zeniv.linux.org.uk>2015-02-05 02:45:00 -0500
commit0ae45f63d4ef8d8eeec49c7d8b44a1775fff13e8 (patch)
tree660dbb014482092361eab263847fb906b5a9ec22 /include/linux/backing-dev.h
parente36f014edff70fc02b3d3d79cead1d58f289332e (diff)
vfs: add support for a lazytime mount option
Add a new mount option which enables a new "lazytime" mode. This mode causes atime, mtime, and ctime updates to only be made to the in-memory version of the inode. The on-disk times will only get updated when (a) if the inode needs to be updated for some non-time related change, (b) if userspace calls fsync(), syncfs() or sync(), or (c) just before an undeleted inode is evicted from memory. This is OK according to POSIX because there are no guarantees after a crash unless userspace explicitly requests via a fsync(2) call. For workloads which feature a large number of random write to a preallocated file, the lazytime mount option significantly reduces writes to the inode table. The repeated 4k writes to a single block will result in undesirable stress on flash devices and SMR disk drives. Even on conventional HDD's, the repeated writes to the inode table block will trigger Adjacent Track Interference (ATI) remediation latencies, which very negatively impact long tail latencies --- which is a very big deal for web serving tiers (for example). Google-Bug-Id: 18297052 Signed-off-by: Theodore Ts'o <tytso@mit.edu> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Diffstat (limited to 'include/linux/backing-dev.h')
-rw-r--r--include/linux/backing-dev.h1
1 files changed, 1 insertions, 0 deletions
diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
index 5da6012b7a14..4cdf7336f64a 100644
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -55,6 +55,7 @@ struct bdi_writeback {
struct list_head b_dirty; /* dirty inodes */
struct list_head b_io; /* parked for writeback */
struct list_head b_more_io; /* parked for more writeback */
+ struct list_head b_dirty_time; /* time stamps are dirty */
spinlock_t list_lock; /* protects the b_* lists */
};