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authorLinus Torvalds <torvalds@linux-foundation.org>2011-07-26 19:39:54 +0200
committerLinus Torvalds <torvalds@linux-foundation.org>2011-07-26 19:39:54 +0200
commitf01ef569cddb1a8627b1c6b3a134998ad1cf4b22 (patch)
tree29ea1a0942c8549c24411e976cd6891c7e995e89 /mm/page-writeback.c
parentMerge branch 'for-linus' of git://git.kernel.dk/linux-block (diff)
parentmm: properly reflect task dirty limits in dirty_exceeded logic (diff)
downloadlinux-f01ef569cddb1a8627b1c6b3a134998ad1cf4b22.tar.xz
linux-f01ef569cddb1a8627b1c6b3a134998ad1cf4b22.zip
Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/wfg/writeback
* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/wfg/writeback: (27 commits) mm: properly reflect task dirty limits in dirty_exceeded logic writeback: don't busy retry writeback on new/freeing inodes writeback: scale IO chunk size up to half device bandwidth writeback: trace global_dirty_state writeback: introduce max-pause and pass-good dirty limits writeback: introduce smoothed global dirty limit writeback: consolidate variable names in balance_dirty_pages() writeback: show bdi write bandwidth in debugfs writeback: bdi write bandwidth estimation writeback: account per-bdi accumulated written pages writeback: make writeback_control.nr_to_write straight writeback: skip tmpfs early in balance_dirty_pages_ratelimited_nr() writeback: trace event writeback_queue_io writeback: trace event writeback_single_inode writeback: remove .nonblocking and .encountered_congestion writeback: remove writeback_control.more_io writeback: skip balance_dirty_pages() for in-memory fs writeback: add bdi_dirty_limit() kernel-doc writeback: avoid extra sync work at enqueue time writeback: elevate queue_io() into wb_writeback() ... Fix up trivial conflicts in fs/fs-writeback.c and mm/filemap.c
Diffstat (limited to 'mm/page-writeback.c')
-rw-r--r--mm/page-writeback.c280
1 files changed, 243 insertions, 37 deletions
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index d8767b381b9c..d1960744f881 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -37,6 +37,16 @@
#include <trace/events/writeback.h>
/*
+ * Sleep at most 200ms at a time in balance_dirty_pages().
+ */
+#define MAX_PAUSE max(HZ/5, 1)
+
+/*
+ * Estimate write bandwidth at 200ms intervals.
+ */
+#define BANDWIDTH_INTERVAL max(HZ/5, 1)
+
+/*
* After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited
* will look to see if it needs to force writeback or throttling.
*/
@@ -111,6 +121,7 @@ EXPORT_SYMBOL(laptop_mode);
/* End of sysctl-exported parameters */
+unsigned long global_dirty_limit;
/*
* Scale the writeback cache size proportional to the relative writeout speeds.
@@ -219,6 +230,7 @@ int dirty_bytes_handler(struct ctl_table *table, int write,
*/
static inline void __bdi_writeout_inc(struct backing_dev_info *bdi)
{
+ __inc_bdi_stat(bdi, BDI_WRITTEN);
__prop_inc_percpu_max(&vm_completions, &bdi->completions,
bdi->max_prop_frac);
}
@@ -244,13 +256,8 @@ void task_dirty_inc(struct task_struct *tsk)
static void bdi_writeout_fraction(struct backing_dev_info *bdi,
long *numerator, long *denominator)
{
- if (bdi_cap_writeback_dirty(bdi)) {
- prop_fraction_percpu(&vm_completions, &bdi->completions,
+ prop_fraction_percpu(&vm_completions, &bdi->completions,
numerator, denominator);
- } else {
- *numerator = 0;
- *denominator = 1;
- }
}
static inline void task_dirties_fraction(struct task_struct *tsk,
@@ -274,12 +281,13 @@ static inline void task_dirties_fraction(struct task_struct *tsk,
* effectively curb the growth of dirty pages. Light dirtiers with high enough
* dirty threshold may never get throttled.
*/
+#define TASK_LIMIT_FRACTION 8
static unsigned long task_dirty_limit(struct task_struct *tsk,
unsigned long bdi_dirty)
{
long numerator, denominator;
unsigned long dirty = bdi_dirty;
- u64 inv = dirty >> 3;
+ u64 inv = dirty / TASK_LIMIT_FRACTION;
task_dirties_fraction(tsk, &numerator, &denominator);
inv *= numerator;
@@ -290,6 +298,12 @@ static unsigned long task_dirty_limit(struct task_struct *tsk,
return max(dirty, bdi_dirty/2);
}
+/* Minimum limit for any task */
+static unsigned long task_min_dirty_limit(unsigned long bdi_dirty)
+{
+ return bdi_dirty - bdi_dirty / TASK_LIMIT_FRACTION;
+}
+
/*
*
*/
@@ -397,6 +411,11 @@ unsigned long determine_dirtyable_memory(void)
return x + 1; /* Ensure that we never return 0 */
}
+static unsigned long hard_dirty_limit(unsigned long thresh)
+{
+ return max(thresh, global_dirty_limit);
+}
+
/*
* global_dirty_limits - background-writeback and dirty-throttling thresholds
*
@@ -435,12 +454,20 @@ void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty)
}
*pbackground = background;
*pdirty = dirty;
+ trace_global_dirty_state(background, dirty);
}
-/*
+/**
* bdi_dirty_limit - @bdi's share of dirty throttling threshold
+ * @bdi: the backing_dev_info to query
+ * @dirty: global dirty limit in pages
*
- * Allocate high/low dirty limits to fast/slow devices, in order to prevent
+ * Returns @bdi's dirty limit in pages. The term "dirty" in the context of
+ * dirty balancing includes all PG_dirty, PG_writeback and NFS unstable pages.
+ * And the "limit" in the name is not seriously taken as hard limit in
+ * balance_dirty_pages().
+ *
+ * It allocates high/low dirty limits to fast/slow devices, in order to prevent
* - starving fast devices
* - piling up dirty pages (that will take long time to sync) on slow devices
*
@@ -468,6 +495,153 @@ unsigned long bdi_dirty_limit(struct backing_dev_info *bdi, unsigned long dirty)
return bdi_dirty;
}
+static void bdi_update_write_bandwidth(struct backing_dev_info *bdi,
+ unsigned long elapsed,
+ unsigned long written)
+{
+ const unsigned long period = roundup_pow_of_two(3 * HZ);
+ unsigned long avg = bdi->avg_write_bandwidth;
+ unsigned long old = bdi->write_bandwidth;
+ u64 bw;
+
+ /*
+ * bw = written * HZ / elapsed
+ *
+ * bw * elapsed + write_bandwidth * (period - elapsed)
+ * write_bandwidth = ---------------------------------------------------
+ * period
+ */
+ bw = written - bdi->written_stamp;
+ bw *= HZ;
+ if (unlikely(elapsed > period)) {
+ do_div(bw, elapsed);
+ avg = bw;
+ goto out;
+ }
+ bw += (u64)bdi->write_bandwidth * (period - elapsed);
+ bw >>= ilog2(period);
+
+ /*
+ * one more level of smoothing, for filtering out sudden spikes
+ */
+ if (avg > old && old >= (unsigned long)bw)
+ avg -= (avg - old) >> 3;
+
+ if (avg < old && old <= (unsigned long)bw)
+ avg += (old - avg) >> 3;
+
+out:
+ bdi->write_bandwidth = bw;
+ bdi->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;
+
+ /*
+ * Follow up in one step.
+ */
+ if (limit < thresh) {
+ limit = thresh;
+ goto update;
+ }
+
+ /*
+ * 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.
+ */
+ thresh = max(thresh, dirty);
+ if (limit > thresh) {
+ limit -= (limit - thresh) >> 5;
+ goto update;
+ }
+ return;
+update:
+ global_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;
+
+ /*
+ * check locklessly first to optimize away locking for the most time
+ */
+ if (time_before(now, update_time + BANDWIDTH_INTERVAL))
+ return;
+
+ spin_lock(&dirty_lock);
+ if (time_after_eq(now, update_time + BANDWIDTH_INTERVAL)) {
+ update_dirty_limit(thresh, dirty);
+ update_time = now;
+ }
+ spin_unlock(&dirty_lock);
+}
+
+void __bdi_update_bandwidth(struct backing_dev_info *bdi,
+ unsigned long thresh,
+ unsigned long dirty,
+ unsigned long bdi_thresh,
+ unsigned long bdi_dirty,
+ unsigned long start_time)
+{
+ unsigned long now = jiffies;
+ unsigned long elapsed = now - bdi->bw_time_stamp;
+ unsigned long written;
+
+ /*
+ * rate-limit, only update once every 200ms.
+ */
+ if (elapsed < BANDWIDTH_INTERVAL)
+ return;
+
+ written = percpu_counter_read(&bdi->bdi_stat[BDI_WRITTEN]);
+
+ /*
+ * Skip quiet periods when disk bandwidth is under-utilized.
+ * (at least 1s idle time between two flusher runs)
+ */
+ if (elapsed > HZ && time_before(bdi->bw_time_stamp, start_time))
+ goto snapshot;
+
+ if (thresh)
+ global_update_bandwidth(thresh, dirty, now);
+
+ bdi_update_write_bandwidth(bdi, elapsed, written);
+
+snapshot:
+ bdi->written_stamp = written;
+ bdi->bw_time_stamp = now;
+}
+
+static void bdi_update_bandwidth(struct backing_dev_info *bdi,
+ unsigned long thresh,
+ unsigned long dirty,
+ unsigned long bdi_thresh,
+ unsigned long bdi_dirty,
+ unsigned long start_time)
+{
+ if (time_is_after_eq_jiffies(bdi->bw_time_stamp + BANDWIDTH_INTERVAL))
+ return;
+ spin_lock(&bdi->wb.list_lock);
+ __bdi_update_bandwidth(bdi, thresh, dirty, bdi_thresh, bdi_dirty,
+ start_time);
+ spin_unlock(&bdi->wb.list_lock);
+}
+
/*
* balance_dirty_pages() must be called by processes which are generating dirty
* data. It looks at the number of dirty pages in the machine and will force
@@ -478,27 +652,25 @@ unsigned long bdi_dirty_limit(struct backing_dev_info *bdi, unsigned long dirty)
static void balance_dirty_pages(struct address_space *mapping,
unsigned long write_chunk)
{
- long nr_reclaimable, bdi_nr_reclaimable;
- long nr_writeback, bdi_nr_writeback;
+ unsigned long nr_reclaimable, bdi_nr_reclaimable;
+ unsigned long nr_dirty; /* = file_dirty + writeback + unstable_nfs */
+ unsigned long bdi_dirty;
unsigned long background_thresh;
unsigned long dirty_thresh;
unsigned long bdi_thresh;
+ unsigned long task_bdi_thresh;
+ unsigned long min_task_bdi_thresh;
unsigned long pages_written = 0;
unsigned long pause = 1;
bool dirty_exceeded = false;
+ bool clear_dirty_exceeded = true;
struct backing_dev_info *bdi = mapping->backing_dev_info;
+ unsigned long start_time = jiffies;
for (;;) {
- struct writeback_control wbc = {
- .sync_mode = WB_SYNC_NONE,
- .older_than_this = NULL,
- .nr_to_write = write_chunk,
- .range_cyclic = 1,
- };
-
nr_reclaimable = global_page_state(NR_FILE_DIRTY) +
global_page_state(NR_UNSTABLE_NFS);
- nr_writeback = global_page_state(NR_WRITEBACK);
+ nr_dirty = nr_reclaimable + global_page_state(NR_WRITEBACK);
global_dirty_limits(&background_thresh, &dirty_thresh);
@@ -507,12 +679,12 @@ static void balance_dirty_pages(struct address_space *mapping,
* catch-up. This avoids (excessively) small writeouts
* when the bdi limits are ramping up.
*/
- if (nr_reclaimable + nr_writeback <=
- (background_thresh + dirty_thresh) / 2)
+ if (nr_dirty <= (background_thresh + dirty_thresh) / 2)
break;
bdi_thresh = bdi_dirty_limit(bdi, dirty_thresh);
- bdi_thresh = task_dirty_limit(current, bdi_thresh);
+ min_task_bdi_thresh = task_min_dirty_limit(bdi_thresh);
+ task_bdi_thresh = task_dirty_limit(current, bdi_thresh);
/*
* In order to avoid the stacked BDI deadlock we need
@@ -524,12 +696,14 @@ static void balance_dirty_pages(struct address_space *mapping,
* actually dirty; with m+n sitting in the percpu
* deltas.
*/
- if (bdi_thresh < 2*bdi_stat_error(bdi)) {
+ if (task_bdi_thresh < 2 * bdi_stat_error(bdi)) {
bdi_nr_reclaimable = bdi_stat_sum(bdi, BDI_RECLAIMABLE);
- bdi_nr_writeback = bdi_stat_sum(bdi, BDI_WRITEBACK);
+ bdi_dirty = bdi_nr_reclaimable +
+ bdi_stat_sum(bdi, BDI_WRITEBACK);
} else {
bdi_nr_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE);
- bdi_nr_writeback = bdi_stat(bdi, BDI_WRITEBACK);
+ bdi_dirty = bdi_nr_reclaimable +
+ bdi_stat(bdi, BDI_WRITEBACK);
}
/*
@@ -538,9 +712,10 @@ static void balance_dirty_pages(struct address_space *mapping,
* bdi or process from holding back light ones; The latter is
* the last resort safeguard.
*/
- dirty_exceeded =
- (bdi_nr_reclaimable + bdi_nr_writeback > bdi_thresh)
- || (nr_reclaimable + nr_writeback > dirty_thresh);
+ dirty_exceeded = (bdi_dirty > task_bdi_thresh) ||
+ (nr_dirty > dirty_thresh);
+ clear_dirty_exceeded = (bdi_dirty <= min_task_bdi_thresh) &&
+ (nr_dirty <= dirty_thresh);
if (!dirty_exceeded)
break;
@@ -548,6 +723,9 @@ static void balance_dirty_pages(struct address_space *mapping,
if (!bdi->dirty_exceeded)
bdi->dirty_exceeded = 1;
+ bdi_update_bandwidth(bdi, dirty_thresh, nr_dirty,
+ bdi_thresh, bdi_dirty, start_time);
+
/* Note: nr_reclaimable denotes nr_dirty + nr_unstable.
* Unstable writes are a feature of certain networked
* filesystems (i.e. NFS) in which data may have been
@@ -557,17 +735,40 @@ static void balance_dirty_pages(struct address_space *mapping,
* threshold otherwise wait until the disk writes catch
* up.
*/
- trace_wbc_balance_dirty_start(&wbc, bdi);
- if (bdi_nr_reclaimable > bdi_thresh) {
- writeback_inodes_wb(&bdi->wb, &wbc);
- pages_written += write_chunk - wbc.nr_to_write;
- trace_wbc_balance_dirty_written(&wbc, bdi);
+ trace_balance_dirty_start(bdi);
+ if (bdi_nr_reclaimable > task_bdi_thresh) {
+ pages_written += writeback_inodes_wb(&bdi->wb,
+ write_chunk);
+ trace_balance_dirty_written(bdi, pages_written);
if (pages_written >= write_chunk)
break; /* We've done our duty */
}
- trace_wbc_balance_dirty_wait(&wbc, bdi);
__set_current_state(TASK_UNINTERRUPTIBLE);
io_schedule_timeout(pause);
+ trace_balance_dirty_wait(bdi);
+
+ dirty_thresh = hard_dirty_limit(dirty_thresh);
+ /*
+ * max-pause area. If dirty exceeded but still within this
+ * area, no need to sleep for more than 200ms: (a) 8 pages per
+ * 200ms is typically more than enough to curb heavy dirtiers;
+ * (b) the pause time limit makes the dirtiers more responsive.
+ */
+ if (nr_dirty < dirty_thresh +
+ dirty_thresh / DIRTY_MAXPAUSE_AREA &&
+ time_after(jiffies, start_time + MAX_PAUSE))
+ break;
+ /*
+ * pass-good area. When some bdi gets blocked (eg. NFS server
+ * not responding), or write bandwidth dropped dramatically due
+ * to concurrent reads, or dirty threshold suddenly dropped and
+ * the dirty pages cannot be brought down anytime soon (eg. on
+ * slow USB stick), at least let go of the good bdi's.
+ */
+ if (nr_dirty < dirty_thresh +
+ dirty_thresh / DIRTY_PASSGOOD_AREA &&
+ bdi_dirty < bdi_thresh)
+ break;
/*
* Increase the delay for each loop, up to our previous
@@ -578,7 +779,8 @@ static void balance_dirty_pages(struct address_space *mapping,
pause = HZ / 10;
}
- if (!dirty_exceeded && bdi->dirty_exceeded)
+ /* Clear dirty_exceeded flag only when no task can exceed the limit */
+ if (clear_dirty_exceeded && bdi->dirty_exceeded)
bdi->dirty_exceeded = 0;
if (writeback_in_progress(bdi))
@@ -626,9 +828,13 @@ static DEFINE_PER_CPU(unsigned long, bdp_ratelimits) = 0;
void balance_dirty_pages_ratelimited_nr(struct address_space *mapping,
unsigned long nr_pages_dirtied)
{
+ struct backing_dev_info *bdi = mapping->backing_dev_info;
unsigned long ratelimit;
unsigned long *p;
+ if (!bdi_cap_account_dirty(bdi))
+ return;
+
ratelimit = ratelimit_pages;
if (mapping->backing_dev_info->dirty_exceeded)
ratelimit = 8;
@@ -892,12 +1098,12 @@ int write_cache_pages(struct address_space *mapping,
range_whole = 1;
cycled = 1; /* ignore range_cyclic tests */
}
- if (wbc->sync_mode == WB_SYNC_ALL)
+ if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
tag = PAGECACHE_TAG_TOWRITE;
else
tag = PAGECACHE_TAG_DIRTY;
retry:
- if (wbc->sync_mode == WB_SYNC_ALL)
+ if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
tag_pages_for_writeback(mapping, index, end);
done_index = index;
while (!done && (index <= end)) {