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Change-Id: I23f6f75979077992298d848efd79a6efc0d776bd
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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>
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A block_device may be attached to different gendisks and thus
different bdis over time. bdev_inode_switch_bdi() is used to switch
the associated bdi. The function assumes that the inode could be
dirty and transfers it between bdis if so. This is a bit nasty in
that it reaches into bdi internals.
This patch reimplements the function so that it writes out the inode
if dirty. This is a lot simpler and can be implemented without
exposing bdi internals.
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Jens Axboe <axboe@fb.com>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
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bdi_destroy() has code to transfer the remaining dirty inodes to the
default_backing_dev_info; however, given the shutdown sequence, it
isn't clear how such condition would happen. Also, it isn't a full
solution as the transferred inodes stlil point to the bdi which is
being destroyed. Operations on those inodes can end up accessing
already released fields such as the percpu stat fields.
Digging through the history, it seems that the code was added as a
quick workaround for a bug report without fully root-causing the
issue. We probably want to remove the code in time but for now let's
add a comment noting that it is a quick workaround.
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@fb.com>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
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Canceling of bdi->wb.dwork is currently a bit mushy.
bdi_wb_shutdown() performs cancel_delayed_work_sync() at the end after
shutting down and flushing the delayed_work and bdi_destroy() tries
yet again after bdi_unregister().
bdi->wb.dwork is queued only after checking BDI_registered while
holding bdi->wb_lock and bdi_wb_shutdown() clears the flag while
holding the same lock and then flushes the delayed_work. There's no
way the delayed_work can be queued again after that.
Replace the two unnecessary cancel_delayed_work_sync() invocations
with WARNs on pending. This simplifies and clarifies the code a bit
and will help future changes in further isolating bdi_writeback
handling.
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@fb.com>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
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The only places where NULL test on bdi->dev is used are
bdi_[un]register(). The functions can't be called in parallel anyway
and there's no point in protecting bdi->dev clearing with a lock.
Remove bdi->wb_lock grabbing around bdi->dev clearing and move it
after device_unregister() call so that bdi->dev doesn't have to be
cached in a local variable.
This patch shouldn't introduce any behavior difference.
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@fb.com>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
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