• Theodore Ts'o's avatar
    vfs: add support for a lazytime mount option · 0ae45f63
    Theodore Ts'o authored
    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's avatarTheodore Ts'o <tytso@mit.edu>
    Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
    0ae45f63
file.c 27.4 KB