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-rw-r--r--mm/page-writeback.c32
1 files changed, 28 insertions, 4 deletions
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 71252486bc6f..50f08241f981 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -411,8 +411,13 @@ void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty)
411 * 411 *
412 * Returns @bdi's dirty limit in pages. The term "dirty" in the context of 412 * Returns @bdi's dirty limit in pages. The term "dirty" in the context of
413 * dirty balancing includes all PG_dirty, PG_writeback and NFS unstable pages. 413 * dirty balancing includes all PG_dirty, PG_writeback and NFS unstable pages.
414 * And the "limit" in the name is not seriously taken as hard limit in 414 *
415 * balance_dirty_pages(). 415 * Note that balance_dirty_pages() will only seriously take it as a hard limit
416 * when sleeping max_pause per page is not enough to keep the dirty pages under
417 * control. For example, when the device is completely stalled due to some error
418 * conditions, or when there are 1000 dd tasks writing to a slow 10MB/s USB key.
419 * In the other normal situations, it acts more gently by throttling the tasks
420 * more (rather than completely block them) when the bdi dirty pages go high.
416 * 421 *
417 * It allocates high/low dirty limits to fast/slow devices, in order to prevent 422 * It allocates high/low dirty limits to fast/slow devices, in order to prevent
418 * - starving fast devices 423 * - starving fast devices
@@ -594,6 +599,13 @@ static unsigned long bdi_position_ratio(struct backing_dev_info *bdi,
594 */ 599 */
595 if (unlikely(bdi_thresh > thresh)) 600 if (unlikely(bdi_thresh > thresh))
596 bdi_thresh = thresh; 601 bdi_thresh = thresh;
602 /*
603 * It's very possible that bdi_thresh is close to 0 not because the
604 * device is slow, but that it has remained inactive for long time.
605 * Honour such devices a reasonable good (hopefully IO efficient)
606 * threshold, so that the occasional writes won't be blocked and active
607 * writes can rampup the threshold quickly.
608 */
597 bdi_thresh = max(bdi_thresh, (limit - dirty) / 8); 609 bdi_thresh = max(bdi_thresh, (limit - dirty) / 8);
598 /* 610 /*
599 * scale global setpoint to bdi's: 611 * scale global setpoint to bdi's:
@@ -977,8 +989,7 @@ static unsigned long bdi_max_pause(struct backing_dev_info *bdi,
977 * 989 *
978 * 8 serves as the safety ratio. 990 * 8 serves as the safety ratio.
979 */ 991 */
980 if (bdi_dirty) 992 t = min(t, bdi_dirty * HZ / (8 * bw + 1));
981 t = min(t, bdi_dirty * HZ / (8 * bw + 1));
982 993
983 /* 994 /*
984 * The pause time will be settled within range (max_pause/4, max_pause). 995 * The pause time will be settled within range (max_pause/4, max_pause).
@@ -1136,6 +1147,19 @@ pause:
1136 if (task_ratelimit) 1147 if (task_ratelimit)
1137 break; 1148 break;
1138 1149
1150 /*
1151 * In the case of an unresponding NFS server and the NFS dirty
1152 * pages exceeds dirty_thresh, give the other good bdi's a pipe
1153 * to go through, so that tasks on them still remain responsive.
1154 *
1155 * In theory 1 page is enough to keep the comsumer-producer
1156 * pipe going: the flusher cleans 1 page => the task dirties 1
1157 * more page. However bdi_dirty has accounting errors. So use
1158 * the larger and more IO friendly bdi_stat_error.
1159 */
1160 if (bdi_dirty <= bdi_stat_error(bdi))
1161 break;
1162
1139 if (fatal_signal_pending(current)) 1163 if (fatal_signal_pending(current))
1140 break; 1164 break;
1141 } 1165 }