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

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)) {