diff options
| author | Jens Axboe <axboe@fb.com> | 2016-04-26 09:14:27 -0600 |
|---|---|---|
| committer | Jens Axboe <axboe@fb.com> | 2016-04-26 09:51:21 -0600 |
| commit | 6edfbb2f08df9cc3bdb65c2f06fce94a39ab6236 (patch) | |
| tree | 801df7406e2066b0e64b809d589df920dca7e429 /include/linux/blkdev.h | |
| parent | 3cd16ff982aafeb88a259d3846c8113feb4bbf28 (diff) | |
writeback: throttle buffered writebackwb-buf-throttle-v5
Test patch that throttles buffered writeback to make it a lot
more smooth, and has way less impact on other system activity.
Background writeback should be, by definition, background
activity. The fact that we flush huge bundles of it at the time
means that it potentially has heavy impacts on foreground workloads,
which isn't ideal. We can't easily limit the sizes of writes that
we do, since that would impact file system layout in the presence
of delayed allocation. So just throttle back buffered writeback,
unless someone is waiting for it.
The algorithm for when to throttle takes its inspiration in the
CoDel networking scheduling algorithm. Like CoDel, blk-wb monitors
the minimum latencies of requests over a window of time. In that
window of time, if the minimum latency of any request exceeds a
given target, then a scale count is incremented and the queue depth
is shrunk. The next monitoring window is shrunk accordingly. Unlike
CoDel, if we hit a window that exhibits good behavior, then we
simply increment the scale count and re-calculate the limits for that
scale value. This prevents us from oscillating between a
close-to-ideal value and max all the time, instead remaining in the
windows where we get good behavior.
The patch registers two sysfs entries. The first one, 'wb_window_usec',
defines the window of monitoring. The second one, 'wb_lat_usec',
sets the latency target for the window. It defaults to 2 msec for
non-rotational storage, and 75 msec for rotational storage. Setting
this value to '0' disables blk-wb. Generally, a user would not have
to touch these settings.
Signed-off-by: Jens Axboe <axboe@fb.com>
Diffstat (limited to 'include/linux/blkdev.h')
| -rw-r--r-- | include/linux/blkdev.h | 6 |
1 files changed, 5 insertions, 1 deletions
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h index 87f6703ced71..a89f46c58d5f 100644 --- a/include/linux/blkdev.h +++ b/include/linux/blkdev.h @@ -24,6 +24,7 @@ #include <linux/rcupdate.h> #include <linux/percpu-refcount.h> #include <linux/scatterlist.h> +#include <linux/wbt.h> struct module; struct scsi_ioctl_command; @@ -37,6 +38,7 @@ struct bsg_job; struct blkcg_gq; struct blk_flush_queue; struct pr_ops; +struct rq_wb; #define BLKDEV_MIN_RQ 4 #define BLKDEV_MAX_RQ 128 /* Default maximum */ @@ -153,7 +155,7 @@ struct request { struct gendisk *rq_disk; struct hd_struct *part; unsigned long start_time; - s64 issue_time; + struct wb_issue_stat wb_stat; #ifdef CONFIG_BLK_CGROUP struct request_list *rl; /* rl this rq is alloced from */ unsigned long long start_time_ns; @@ -291,6 +293,8 @@ struct request_queue { int nr_rqs[2]; /* # allocated [a]sync rqs */ int nr_rqs_elvpriv; /* # allocated rqs w/ elvpriv */ + struct rq_wb *rq_wb; + /* * If blkcg is not used, @q->root_rl serves all requests. If blkcg * is used, root blkg allocates from @q->root_rl and all other |