[PATCH 05/19] writeback: move global_dirty_limit into wb_domain

Tejun Heo
2015-04-06T20:05:05Z

This patch is a part of the series to define wb_domain which
represents a domain that wb's (bdi_writeback's) belong to and are
measured against each other in. This will enable IO backpressure
propagation for cgroup writeback.

global_dirty_limit exists to regulate the global dirty threshold which
is a property of the wb_domain. This patch moves hard_dirty_limit,
dirty_lock, and update_time into wb_domain.

This is pure reorganization and doesn't introduce any behavioral
changes.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Jan Kara <jack@suse.cz>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Greg Thelen <gthelen@google.com>
---
fs/fs-writeback.c | 2 +-
include/linux/writeback.h | 17 ++++++++++++++-
include/trace/events/writeback.h | 7 +++---
mm/page-writeback.c | 46 ++++++++++++++++++++--------------------
4 files changed, 44 insertions(+), 28 deletions(-)

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 85daae2..5b842bd 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -868,7 +868,7 @@ static long writeback_chunk_size(struct bdi_writeback *wb,
pages = LONG_MAX;
else {
pages = min(wb->avg_write_bandwidth / 2,
- global_dirty_limit / DIRTY_SCOPE);
+ global_wb_domain.dirty_limit / DIRTY_SCOPE);
pages = min(pages, work->nr_pages);
pages = round_down(pages + MIN_WRITEBACK_PAGES,
MIN_WRITEBACK_PAGES);
diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index 4972dcf..fe0924a 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -95,6 +95,8 @@ struct writeback_control {
* dirtyable memory accordingly.
*/
struct wb_domain {
+ spinlock_t lock;
+
/*
* Scale the writeback cache size proportional to the relative
* writeout speed.
@@ -115,6 +117,19 @@ struct wb_domain {
struct fprop_global completions;
struct timer_list period_timer; /* timer for aging of completions */
unsigned long period_time;
+
+ /*
+ * The dirtyable memory and dirty threshold could be suddenly
+ * knocked down by a large amount (eg. on the startup of KVM in a
+ * swapless system). This may throw the system into deep dirty
+ * exceeded state and throttle heavy/light dirtiers alike. To
+ * retain good responsiveness, maintain global_dirty_limit for
+ * tracking slowly down to the knocked down dirty threshold.
+ *
+ * Both fields are protected by ->lock.
+ */
+ unsigned long dirty_limit_tstamp;
+ unsigned long dirty_limit;
};

/*
@@ -153,7 +168,7 @@ void throttle_vm_writeout(gfp_t gfp_mask);
bool zone_dirty_ok(struct zone *zone);
int wb_domain_init(struct wb_domain *dom, gfp_t gfp);

-extern unsigned long global_dirty_limit;
+extern struct wb_domain global_wb_domain;

/* These are exported to sysctl. */
extern int dirty_background_ratio;
diff --git a/include/trace/events/writeback.h b/include/trace/events/writeback.h
index 5c9a68c..d5ac3dd 100644
--- a/include/trace/events/writeback.h
+++ b/include/trace/events/writeback.h
@@ -344,7 +344,7 @@ TRACE_EVENT(global_dirty_state,
__entry->nr_written = global_page_state(NR_WRITTEN);
__entry->background_thresh = background_thresh;
__entry->dirty_thresh = dirty_thresh;
- __entry->dirty_limit = global_dirty_limit;
+ __entry->dirty_limit = global_wb_domain.dirty_limit;
),

TP_printk("dirty=%lu writeback=%lu unstable=%lu "
@@ -446,8 +446,9 @@ TRACE_EVENT(balance_dirty_pages,
unsigned long freerun = (thresh + bg_thresh) / 2;
strlcpy(__entry->bdi, dev_name(bdi->dev), 32);

- __entry->limit = global_dirty_limit;
- __entry->setpoint = (global_dirty_limit + freerun) / 2;
+ __entry->limit = global_wb_domain.dirty_limit;
+ __entry->setpoint = (global_wb_domain.dirty_limit +
+ freerun) / 2;
__entry->dirty = dirty;
__entry->bdi_setpoint = __entry->setpoint *
bdi_thresh / (thresh + 1);
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 43380dc..c141533 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -122,9 +122,7 @@ EXPORT_SYMBOL(laptop_mode);

/* End of sysctl-exported parameters */

-unsigned long global_dirty_limit;
-
-static struct wb_domain global_wb_domain;
+struct wb_domain global_wb_domain;

/*
* Length of period for aging writeout fractions of bdis. This is an
@@ -470,9 +468,15 @@ static void writeout_period(unsigned long t)
int wb_domain_init(struct wb_domain *dom, gfp_t gfp)
{
memset(dom, 0, sizeof(*dom));
+
+ spin_lock_init(&dom->lock);
+
init_timer_deferrable(&dom->period_timer);
dom->period_timer.function = writeout_period;
dom->period_timer.data = (unsigned long)dom;
+
+ dom->dirty_limit_tstamp = jiffies;
+
return fprop_global_init(&dom->completions, gfp);
}

@@ -532,7 +536,9 @@ static unsigned long dirty_freerun_ceiling(unsigned long thresh,

static unsigned long hard_dirty_limit(unsigned long thresh)
{
- return max(thresh, global_dirty_limit);
+ struct wb_domain *dom = &global_wb_domain;
+
+ return max(thresh, dom->dirty_limit);
}

/**
@@ -916,17 +922,10 @@ out:
wb->avg_write_bandwidth = avg;
}

-/*
- * The global dirtyable memory and dirty threshold could be suddenly knocked
- * down by a large amount (eg. on the startup of KVM in a swapless system).
- * This may throw the system into deep dirty exceeded state and throttle
- * heavy/light dirtiers alike. To retain good responsiveness, maintain
- * global_dirty_limit for tracking slowly down to the knocked down dirty
- * threshold.
- */
static void update_dirty_limit(unsigned long thresh, unsigned long dirty)
{
- unsigned long limit = global_dirty_limit;
+ struct wb_domain *dom = &global_wb_domain;
+ unsigned long limit = dom->dirty_limit;

/*
* Follow up in one step.
@@ -939,7 +938,7 @@ static void update_dirty_limit(unsigned long thresh, unsigned long dirty)
/*
* Follow down slowly. Use the higher one as the target, because thresh
* may drop below dirty. This is exactly the reason to introduce
- * global_dirty_limit which is guaranteed to lie above the dirty pages.
+ * dom->dirty_limit which is guaranteed to lie above the dirty pages.
*/
thresh = max(thresh, dirty);
if (limit > thresh) {
@@ -948,28 +947,27 @@ static void update_dirty_limit(unsigned long thresh, unsigned long dirty)
}
return;
update:
- global_dirty_limit = limit;
+ dom->dirty_limit = limit;
}

static void global_update_bandwidth(unsigned long thresh,
unsigned long dirty,
unsigned long now)
{
- static DEFINE_SPINLOCK(dirty_lock);
- static unsigned long update_time = INITIAL_JIFFIES;
+ struct wb_domain *dom = &global_wb_domain;

/*
* check locklessly first to optimize away locking for the most time
*/
- if (time_before(now, update_time + BANDWIDTH_INTERVAL))
+ if (time_before(now, dom->dirty_limit_tstamp + BANDWIDTH_INTERVAL))
return;

- spin_lock(&dirty_lock);
- if (time_after_eq(now, update_time + BANDWIDTH_INTERVAL)) {
+ spin_lock(&dom->lock);
+ if (time_after_eq(now, dom->dirty_limit_tstamp + BANDWIDTH_INTERVAL)) {
update_dirty_limit(thresh, dirty);
- update_time = now;
+ dom->dirty_limit_tstamp = now;
}
- spin_unlock(&dirty_lock);
+ spin_unlock(&dom->lock);
}

/*
@@ -1761,10 +1759,12 @@ void laptop_sync_completion(void)

void writeback_set_ratelimit(void)
{
+ struct wb_domain *dom = &global_wb_domain;
unsigned long background_thresh;
unsigned long dirty_thresh;
+
global_dirty_limits(&background_thresh, &dirty_thresh);
- global_dirty_limit = dirty_thresh;
+ dom->dirty_limit = dirty_thresh;
ratelimit_pages = dirty_thresh / (num_online_cpus() * 32);
if (ratelimit_pages < 16)
ratelimit_pages = 16;
--
2.1.0