1 files changed, 33 insertions, 62 deletions

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index ea0b7cb4a8c7..2cf69a5e46e6 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -253,32 +253,6 @@ static void bdi_writeout_fraction(struct backing_dev_info *bdi,
         }
 }
 
-/*
- * Clip the earned share of dirty pages to that which is actually available.
- * This avoids exceeding the total dirty_limit when the floating averages
- * fluctuate too quickly.
- */
-static void clip_bdi_dirty_limit(struct backing_dev_info *bdi,
-                unsigned long dirty, unsigned long *pbdi_dirty)
-{
-        unsigned long avail_dirty;
-
-        avail_dirty = global_page_state(NR_FILE_DIRTY) +
-                 global_page_state(NR_WRITEBACK) +
-                 global_page_state(NR_UNSTABLE_NFS) +
-                 global_page_state(NR_WRITEBACK_TEMP);
-
-        if (avail_dirty < dirty)
-                avail_dirty = dirty - avail_dirty;
-        else
-                avail_dirty = 0;
-
-        avail_dirty += bdi_stat(bdi, BDI_RECLAIMABLE) +
-                bdi_stat(bdi, BDI_WRITEBACK);
-
-        *pbdi_dirty = min(*pbdi_dirty, avail_dirty);
-}
-
 static inline void task_dirties_fraction(struct task_struct *tsk,
                 long *numerator, long *denominator)
 {
@@ -469,7 +443,6 @@ get_dirty_limits(unsigned long *pbackground, unsigned long *pdirty,
                         bdi_dirty = dirty * bdi->max_ratio / 100;
 
                 *pbdi_dirty = bdi_dirty;
-                clip_bdi_dirty_limit(bdi, dirty, pbdi_dirty);
                 task_dirty_limit(current, pbdi_dirty);
         }
 }
@@ -491,7 +464,7 @@ static void balance_dirty_pages(struct address_space *mapping,
         unsigned long bdi_thresh;
         unsigned long pages_written = 0;
         unsigned long pause = 1;
-
+        bool dirty_exceeded = false;
         struct backing_dev_info *bdi = mapping->backing_dev_info;
 
         for (;;) {
@@ -509,10 +482,35 @@ static void balance_dirty_pages(struct address_space *mapping,
                                         global_page_state(NR_UNSTABLE_NFS);
                 nr_writeback = global_page_state(NR_WRITEBACK);
 
-                bdi_nr_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE);
-                bdi_nr_writeback = bdi_stat(bdi, BDI_WRITEBACK);
+                /*
+                 * In order to avoid the stacked BDI deadlock we need
+                 * to ensure we accurately count the 'dirty' pages when
+                 * the threshold is low.
+                 *
+                 * Otherwise it would be possible to get thresh+n pages
+                 * reported dirty, even though there are thresh-m pages
+                 * actually dirty; with m+n sitting in the percpu
+                 * deltas.
+                 */
+                if (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);
+                } else {
+                        bdi_nr_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE);
+                        bdi_nr_writeback = bdi_stat(bdi, BDI_WRITEBACK);
+                }
 
-                if (bdi_nr_reclaimable + bdi_nr_writeback <= bdi_thresh)
+                /*
+                 * The bdi thresh is somehow "soft" limit derived from the
+                 * global "hard" limit. The former helps to prevent heavy IO
+                 * 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);
+
+                if (!dirty_exceeded)
                         break;
 
                 /*
@@ -540,34 +538,10 @@ static void balance_dirty_pages(struct address_space *mapping,
                 if (bdi_nr_reclaimable > bdi_thresh) {
                         writeback_inodes_wb(&bdi->wb, &wbc);
                         pages_written += write_chunk - wbc.nr_to_write;
-                        get_dirty_limits(&background_thresh, &dirty_thresh,
-                                       &bdi_thresh, bdi);
                         trace_wbc_balance_dirty_written(&wbc, bdi);
+                        if (pages_written >= write_chunk)
+                                break;          /* We've done our duty */
                 }
-
-                /*
-                 * In order to avoid the stacked BDI deadlock we need
-                 * to ensure we accurately count the 'dirty' pages when
-                 * the threshold is low.
-                 *
-                 * Otherwise it would be possible to get thresh+n pages
-                 * reported dirty, even though there are thresh-m pages
-                 * actually dirty; with m+n sitting in the percpu
-                 * deltas.
-                 */
-                if (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);
-                } else if (bdi_nr_reclaimable) {
-                        bdi_nr_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE);
-                        bdi_nr_writeback = bdi_stat(bdi, BDI_WRITEBACK);
-                }
-
-                if (bdi_nr_reclaimable + bdi_nr_writeback <= bdi_thresh)
-                        break;
-                if (pages_written >= write_chunk)
-                        break;          /* We've done our duty */
-
                 trace_wbc_balance_dirty_wait(&wbc, bdi);
                 __set_current_state(TASK_INTERRUPTIBLE);
                 io_schedule_timeout(pause);
@@ -581,8 +555,7 @@ static void balance_dirty_pages(struct address_space *mapping,
                         pause = HZ / 10;
         }
 
-        if (bdi_nr_reclaimable + bdi_nr_writeback < bdi_thresh &&
-                        bdi->dirty_exceeded)
+        if (!dirty_exceeded && bdi->dirty_exceeded)
                 bdi->dirty_exceeded = 0;
 
         if (writeback_in_progress(bdi))
@@ -597,9 +570,7 @@ static void balance_dirty_pages(struct address_space *mapping,
          * background_thresh, to keep the amount of dirty memory low.
          */
         if ((laptop_mode && pages_written) ||
-            (!laptop_mode && ((global_page_state(NR_FILE_DIRTY)
-                               + global_page_state(NR_UNSTABLE_NFS))
-                                          > background_thresh)))
+            (!laptop_mode && (nr_reclaimable > background_thresh)))
                 bdi_start_background_writeback(bdi);
 }