Merge branch 'writeback-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/wfg/linux
* 'writeback-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/wfg/linux:
writeback: move MIN_WRITEBACK_PAGES to fs-writeback.c
writeback: balanced_rate cannot exceed write bandwidth
writeback: do strict bdi dirty_exceeded
writeback: avoid tiny dirty poll intervals
writeback: max, min and target dirty pause time
writeback: dirty ratelimit - think time compensation
btrfs: fix dirtied pages accounting on sub-page writes
writeback: fix dirtied pages accounting on redirty
writeback: fix dirtied pages accounting on sub-page writes
writeback: charge leaked page dirties to active tasks
writeback: Include all dirty inodes in background writeback
diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 20375e6..034d985 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -1136,7 +1136,8 @@
GFP_NOFS);
}
for (i = 0; i < num_pages; i++) {
- clear_page_dirty_for_io(pages[i]);
+ if (clear_page_dirty_for_io(pages[i]))
+ account_page_redirty(pages[i]);
set_page_extent_mapped(pages[i]);
WARN_ON(!PageLocked(pages[i]));
}
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index e295150..f855916 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -20,6 +20,7 @@
#include <linux/sched.h>
#include <linux/fs.h>
#include <linux/mm.h>
+#include <linux/pagemap.h>
#include <linux/kthread.h>
#include <linux/freezer.h>
#include <linux/writeback.h>
@@ -29,6 +30,11 @@
#include "internal.h"
/*
+ * 4MB minimal write chunk size
+ */
+#define MIN_WRITEBACK_PAGES (4096UL >> (PAGE_CACHE_SHIFT - 10))
+
+/*
* Passed into wb_writeback(), essentially a subset of writeback_control
*/
struct wb_writeback_work {
@@ -742,11 +748,17 @@
if (work->for_background && !over_bground_thresh(wb->bdi))
break;
+ /*
+ * Kupdate and background works are special and we want to
+ * include all inodes that need writing. Livelock avoidance is
+ * handled by these works yielding to any other work so we are
+ * safe.
+ */
if (work->for_kupdate) {
oldest_jif = jiffies -
msecs_to_jiffies(dirty_expire_interval * 10);
- work->older_than_this = &oldest_jif;
- }
+ } else if (work->for_background)
+ oldest_jif = jiffies;
trace_writeback_start(wb->bdi, work);
if (list_empty(&wb->b_io))
diff --git a/include/linux/sched.h b/include/linux/sched.h
index f044f66..21cd030 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1544,6 +1544,7 @@
*/
int nr_dirtied;
int nr_dirtied_pause;
+ unsigned long dirty_paused_when; /* start of a write-and-pause period */
#ifdef CONFIG_LATENCYTOP
int latency_record_count;
diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index 6dff473..995b8bf 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -7,6 +7,8 @@
#include <linux/sched.h>
#include <linux/fs.h>
+DECLARE_PER_CPU(int, dirty_throttle_leaks);
+
/*
* The 1/4 region under the global dirty thresh is for smooth dirty throttling:
*
@@ -23,11 +25,6 @@
#define DIRTY_SCOPE 8
#define DIRTY_FULL_SCOPE (DIRTY_SCOPE / 2)
-/*
- * 4MB minimal write chunk size
- */
-#define MIN_WRITEBACK_PAGES (4096UL >> (PAGE_CACHE_SHIFT - 10))
-
struct backing_dev_info;
/*
@@ -194,6 +191,8 @@
void tag_pages_for_writeback(struct address_space *mapping,
pgoff_t start, pgoff_t end);
+void account_page_redirty(struct page *page);
+
/* pdflush.c */
extern int nr_pdflush_threads; /* Global so it can be exported to sysctl
read-only. */
diff --git a/include/trace/events/writeback.h b/include/trace/events/writeback.h
index 99d1d0d..8588a89 100644
--- a/include/trace/events/writeback.h
+++ b/include/trace/events/writeback.h
@@ -300,12 +300,13 @@
unsigned long dirty_ratelimit,
unsigned long task_ratelimit,
unsigned long dirtied,
+ unsigned long period,
long pause,
unsigned long start_time),
TP_ARGS(bdi, thresh, bg_thresh, dirty, bdi_thresh, bdi_dirty,
dirty_ratelimit, task_ratelimit,
- dirtied, pause, start_time),
+ dirtied, period, pause, start_time),
TP_STRUCT__entry(
__array( char, bdi, 32)
@@ -320,6 +321,8 @@
__field(unsigned int, dirtied_pause)
__field(unsigned long, paused)
__field( long, pause)
+ __field(unsigned long, period)
+ __field( long, think)
),
TP_fast_assign(
@@ -336,6 +339,9 @@
__entry->task_ratelimit = KBps(task_ratelimit);
__entry->dirtied = dirtied;
__entry->dirtied_pause = current->nr_dirtied_pause;
+ __entry->think = current->dirty_paused_when == 0 ? 0 :
+ (long)(jiffies - current->dirty_paused_when) * 1000/HZ;
+ __entry->period = period * 1000 / HZ;
__entry->pause = pause * 1000 / HZ;
__entry->paused = (jiffies - start_time) * 1000 / HZ;
),
@@ -346,7 +352,7 @@
"bdi_setpoint=%lu bdi_dirty=%lu "
"dirty_ratelimit=%lu task_ratelimit=%lu "
"dirtied=%u dirtied_pause=%u "
- "paused=%lu pause=%ld",
+ "paused=%lu pause=%ld period=%lu think=%ld",
__entry->bdi,
__entry->limit,
__entry->setpoint,
@@ -358,7 +364,9 @@
__entry->dirtied,
__entry->dirtied_pause,
__entry->paused, /* ms */
- __entry->pause /* ms */
+ __entry->pause, /* ms */
+ __entry->period, /* ms */
+ __entry->think /* ms */
)
);
diff --git a/kernel/exit.c b/kernel/exit.c
index d9eab2e..94ed6e2 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -51,6 +51,7 @@
#include <trace/events/sched.h>
#include <linux/hw_breakpoint.h>
#include <linux/oom.h>
+#include <linux/writeback.h>
#include <asm/uaccess.h>
#include <asm/unistd.h>
@@ -1035,6 +1036,8 @@
validate_creds_for_do_exit(tsk);
preempt_disable();
+ if (tsk->nr_dirtied)
+ __this_cpu_add(dirty_throttle_leaks, tsk->nr_dirtied);
exit_rcu();
/* causes final put_task_struct in finish_task_switch(). */
tsk->state = TASK_DEAD;
diff --git a/kernel/fork.c b/kernel/fork.c
index 5e1391b..443f512 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1294,6 +1294,7 @@
p->nr_dirtied = 0;
p->nr_dirtied_pause = 128 >> (PAGE_SHIFT - 10);
+ p->dirty_paused_when = 0;
/*
* Ok, make it visible to the rest of the system.
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 5cdd4f2..363ba70 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -42,6 +42,12 @@
#define MAX_PAUSE max(HZ/5, 1)
/*
+ * Try to keep balance_dirty_pages() call intervals higher than this many pages
+ * by raising pause time to max_pause when falls below it.
+ */
+#define DIRTY_POLL_THRESH (128 >> (PAGE_SHIFT - 10))
+
+/*
* Estimate write bandwidth at 200ms intervals.
*/
#define BANDWIDTH_INTERVAL max(HZ/5, 1)
@@ -898,6 +904,11 @@
*/
balanced_dirty_ratelimit = div_u64((u64)task_ratelimit * write_bw,
dirty_rate | 1);
+ /*
+ * balanced_dirty_ratelimit ~= (write_bw / N) <= write_bw
+ */
+ if (unlikely(balanced_dirty_ratelimit > write_bw))
+ balanced_dirty_ratelimit = write_bw;
/*
* We could safely do this and return immediately:
@@ -1044,25 +1055,11 @@
return 1;
}
-static unsigned long bdi_max_pause(struct backing_dev_info *bdi,
- unsigned long bdi_dirty)
+static long bdi_max_pause(struct backing_dev_info *bdi,
+ unsigned long bdi_dirty)
{
- unsigned long bw = bdi->avg_write_bandwidth;
- unsigned long hi = ilog2(bw);
- unsigned long lo = ilog2(bdi->dirty_ratelimit);
- unsigned long t;
-
- /* target for 20ms max pause on 1-dd case */
- t = HZ / 50;
-
- /*
- * Scale up pause time for concurrent dirtiers in order to reduce CPU
- * overheads.
- *
- * (N * 20ms) on 2^N concurrent tasks.
- */
- if (hi > lo)
- t += (hi - lo) * (20 * HZ) / 1024;
+ long bw = bdi->avg_write_bandwidth;
+ long t;
/*
* Limit pause time for small memory systems. If sleeping for too long
@@ -1071,13 +1068,85 @@
*
* 8 serves as the safety ratio.
*/
- t = min(t, bdi_dirty * HZ / (8 * bw + 1));
+ t = bdi_dirty / (1 + bw / roundup_pow_of_two(1 + HZ / 8));
+ t++;
+
+ return min_t(long, t, MAX_PAUSE);
+}
+
+static long bdi_min_pause(struct backing_dev_info *bdi,
+ long max_pause,
+ unsigned long task_ratelimit,
+ unsigned long dirty_ratelimit,
+ int *nr_dirtied_pause)
+{
+ long hi = ilog2(bdi->avg_write_bandwidth);
+ long lo = ilog2(bdi->dirty_ratelimit);
+ long t; /* target pause */
+ long pause; /* estimated next pause */
+ int pages; /* target nr_dirtied_pause */
+
+ /* target for 10ms pause on 1-dd case */
+ t = max(1, HZ / 100);
/*
- * The pause time will be settled within range (max_pause/4, max_pause).
- * Apply a minimal value of 4 to get a non-zero max_pause/4.
+ * Scale up pause time for concurrent dirtiers in order to reduce CPU
+ * overheads.
+ *
+ * (N * 10ms) on 2^N concurrent tasks.
*/
- return clamp_val(t, 4, MAX_PAUSE);
+ if (hi > lo)
+ t += (hi - lo) * (10 * HZ) / 1024;
+
+ /*
+ * This is a bit convoluted. We try to base the next nr_dirtied_pause
+ * on the much more stable dirty_ratelimit. However the next pause time
+ * will be computed based on task_ratelimit and the two rate limits may
+ * depart considerably at some time. Especially if task_ratelimit goes
+ * below dirty_ratelimit/2 and the target pause is max_pause, the next
+ * pause time will be max_pause*2 _trimmed down_ to max_pause. As a
+ * result task_ratelimit won't be executed faithfully, which could
+ * eventually bring down dirty_ratelimit.
+ *
+ * We apply two rules to fix it up:
+ * 1) try to estimate the next pause time and if necessary, use a lower
+ * nr_dirtied_pause so as not to exceed max_pause. When this happens,
+ * nr_dirtied_pause will be "dancing" with task_ratelimit.
+ * 2) limit the target pause time to max_pause/2, so that the normal
+ * small fluctuations of task_ratelimit won't trigger rule (1) and
+ * nr_dirtied_pause will remain as stable as dirty_ratelimit.
+ */
+ t = min(t, 1 + max_pause / 2);
+ pages = dirty_ratelimit * t / roundup_pow_of_two(HZ);
+
+ /*
+ * Tiny nr_dirtied_pause is found to hurt I/O performance in the test
+ * case fio-mmap-randwrite-64k, which does 16*{sync read, async write}.
+ * When the 16 consecutive reads are often interrupted by some dirty
+ * throttling pause during the async writes, cfq will go into idles
+ * (deadline is fine). So push nr_dirtied_pause as high as possible
+ * until reaches DIRTY_POLL_THRESH=32 pages.
+ */
+ if (pages < DIRTY_POLL_THRESH) {
+ t = max_pause;
+ pages = dirty_ratelimit * t / roundup_pow_of_two(HZ);
+ if (pages > DIRTY_POLL_THRESH) {
+ pages = DIRTY_POLL_THRESH;
+ t = HZ * DIRTY_POLL_THRESH / dirty_ratelimit;
+ }
+ }
+
+ pause = HZ * pages / (task_ratelimit + 1);
+ if (pause > max_pause) {
+ t = max_pause;
+ pages = task_ratelimit * t / roundup_pow_of_two(HZ);
+ }
+
+ *nr_dirtied_pause = pages;
+ /*
+ * The minimal pause time will normally be half the target pause time.
+ */
+ return pages >= DIRTY_POLL_THRESH ? 1 + t / 2 : t;
}
/*
@@ -1098,16 +1167,21 @@
unsigned long background_thresh;
unsigned long dirty_thresh;
unsigned long bdi_thresh;
- long pause = 0;
- long uninitialized_var(max_pause);
+ long period;
+ long pause;
+ long max_pause;
+ long min_pause;
+ int nr_dirtied_pause;
bool dirty_exceeded = false;
unsigned long task_ratelimit;
- unsigned long uninitialized_var(dirty_ratelimit);
+ unsigned long dirty_ratelimit;
unsigned long pos_ratio;
struct backing_dev_info *bdi = mapping->backing_dev_info;
unsigned long start_time = jiffies;
for (;;) {
+ unsigned long now = jiffies;
+
/*
* Unstable writes are a feature of certain networked
* filesystems (i.e. NFS) in which data may have been
@@ -1127,8 +1201,13 @@
*/
freerun = dirty_freerun_ceiling(dirty_thresh,
background_thresh);
- if (nr_dirty <= freerun)
+ if (nr_dirty <= freerun) {
+ current->dirty_paused_when = now;
+ current->nr_dirtied = 0;
+ current->nr_dirtied_pause =
+ dirty_poll_interval(nr_dirty, dirty_thresh);
break;
+ }
if (unlikely(!writeback_in_progress(bdi)))
bdi_start_background_writeback(bdi);
@@ -1168,7 +1247,7 @@
bdi_stat(bdi, BDI_WRITEBACK);
}
- dirty_exceeded = (bdi_dirty > bdi_thresh) ||
+ dirty_exceeded = (bdi_dirty > bdi_thresh) &&
(nr_dirty > dirty_thresh);
if (dirty_exceeded && !bdi->dirty_exceeded)
bdi->dirty_exceeded = 1;
@@ -1177,20 +1256,34 @@
nr_dirty, bdi_thresh, bdi_dirty,
start_time);
- max_pause = bdi_max_pause(bdi, bdi_dirty);
-
dirty_ratelimit = bdi->dirty_ratelimit;
pos_ratio = bdi_position_ratio(bdi, dirty_thresh,
background_thresh, nr_dirty,
bdi_thresh, bdi_dirty);
task_ratelimit = ((u64)dirty_ratelimit * pos_ratio) >>
RATELIMIT_CALC_SHIFT;
+ max_pause = bdi_max_pause(bdi, bdi_dirty);
+ min_pause = bdi_min_pause(bdi, max_pause,
+ task_ratelimit, dirty_ratelimit,
+ &nr_dirtied_pause);
+
if (unlikely(task_ratelimit == 0)) {
+ period = max_pause;
pause = max_pause;
goto pause;
}
- pause = HZ * pages_dirtied / task_ratelimit;
- if (unlikely(pause <= 0)) {
+ period = HZ * pages_dirtied / task_ratelimit;
+ pause = period;
+ if (current->dirty_paused_when)
+ pause -= now - current->dirty_paused_when;
+ /*
+ * For less than 1s think time (ext3/4 may block the dirtier
+ * for up to 800ms from time to time on 1-HDD; so does xfs,
+ * however at much less frequency), try to compensate it in
+ * future periods by updating the virtual time; otherwise just
+ * do a reset, as it may be a light dirtier.
+ */
+ if (pause < min_pause) {
trace_balance_dirty_pages(bdi,
dirty_thresh,
background_thresh,
@@ -1200,12 +1293,24 @@
dirty_ratelimit,
task_ratelimit,
pages_dirtied,
- pause,
+ period,
+ min(pause, 0L),
start_time);
- pause = 1; /* avoid resetting nr_dirtied_pause below */
+ if (pause < -HZ) {
+ current->dirty_paused_when = now;
+ current->nr_dirtied = 0;
+ } else if (period) {
+ current->dirty_paused_when += period;
+ current->nr_dirtied = 0;
+ } else if (current->nr_dirtied_pause <= pages_dirtied)
+ current->nr_dirtied_pause += pages_dirtied;
break;
}
- pause = min(pause, max_pause);
+ if (unlikely(pause > max_pause)) {
+ /* for occasional dropped task_ratelimit */
+ now += min(pause - max_pause, max_pause);
+ pause = max_pause;
+ }
pause:
trace_balance_dirty_pages(bdi,
@@ -1217,11 +1322,16 @@
dirty_ratelimit,
task_ratelimit,
pages_dirtied,
+ period,
pause,
start_time);
__set_current_state(TASK_KILLABLE);
io_schedule_timeout(pause);
+ current->dirty_paused_when = now + pause;
+ current->nr_dirtied = 0;
+ current->nr_dirtied_pause = nr_dirtied_pause;
+
/*
* This is typically equal to (nr_dirty < dirty_thresh) and can
* also keep "1000+ dd on a slow USB stick" under control.
@@ -1249,23 +1359,6 @@
if (!dirty_exceeded && bdi->dirty_exceeded)
bdi->dirty_exceeded = 0;
- current->nr_dirtied = 0;
- if (pause == 0) { /* in freerun area */
- current->nr_dirtied_pause =
- dirty_poll_interval(nr_dirty, dirty_thresh);
- } else if (pause <= max_pause / 4 &&
- pages_dirtied >= current->nr_dirtied_pause) {
- current->nr_dirtied_pause = clamp_val(
- dirty_ratelimit * (max_pause / 2) / HZ,
- pages_dirtied + pages_dirtied / 8,
- pages_dirtied * 4);
- } else if (pause >= max_pause) {
- current->nr_dirtied_pause = 1 | clamp_val(
- dirty_ratelimit * (max_pause / 2) / HZ,
- pages_dirtied / 4,
- pages_dirtied - pages_dirtied / 8);
- }
-
if (writeback_in_progress(bdi))
return;
@@ -1296,6 +1389,22 @@
static DEFINE_PER_CPU(int, bdp_ratelimits);
+/*
+ * Normal tasks are throttled by
+ * loop {
+ * dirty tsk->nr_dirtied_pause pages;
+ * take a snap in balance_dirty_pages();
+ * }
+ * However there is a worst case. If every task exit immediately when dirtied
+ * (tsk->nr_dirtied_pause - 1) pages, balance_dirty_pages() will never be
+ * called to throttle the page dirties. The solution is to save the not yet
+ * throttled page dirties in dirty_throttle_leaks on task exit and charge them
+ * randomly into the running tasks. This works well for the above worst case,
+ * as the new task will pick up and accumulate the old task's leaked dirty
+ * count and eventually get throttled.
+ */
+DEFINE_PER_CPU(int, dirty_throttle_leaks) = 0;
+
/**
* balance_dirty_pages_ratelimited_nr - balance dirty memory state
* @mapping: address_space which was dirtied
@@ -1324,8 +1433,6 @@
if (bdi->dirty_exceeded)
ratelimit = min(ratelimit, 32 >> (PAGE_SHIFT - 10));
- current->nr_dirtied += nr_pages_dirtied;
-
preempt_disable();
/*
* This prevents one CPU to accumulate too many dirtied pages without
@@ -1336,12 +1443,20 @@
p = &__get_cpu_var(bdp_ratelimits);
if (unlikely(current->nr_dirtied >= ratelimit))
*p = 0;
- else {
- *p += nr_pages_dirtied;
- if (unlikely(*p >= ratelimit_pages)) {
- *p = 0;
- ratelimit = 0;
- }
+ else if (unlikely(*p >= ratelimit_pages)) {
+ *p = 0;
+ ratelimit = 0;
+ }
+ /*
+ * Pick up the dirtied pages by the exited tasks. This avoids lots of
+ * short-lived tasks (eg. gcc invocations in a kernel build) escaping
+ * the dirty throttling and livelock other long-run dirtiers.
+ */
+ p = &__get_cpu_var(dirty_throttle_leaks);
+ if (*p > 0 && current->nr_dirtied < ratelimit) {
+ nr_pages_dirtied = min(*p, ratelimit - current->nr_dirtied);
+ *p -= nr_pages_dirtied;
+ current->nr_dirtied += nr_pages_dirtied;
}
preempt_enable();
@@ -1823,6 +1938,8 @@
__inc_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE);
__inc_bdi_stat(mapping->backing_dev_info, BDI_DIRTIED);
task_io_account_write(PAGE_CACHE_SIZE);
+ current->nr_dirtied++;
+ this_cpu_inc(bdp_ratelimits);
}
}
EXPORT_SYMBOL(account_page_dirtied);
@@ -1883,6 +2000,24 @@
EXPORT_SYMBOL(__set_page_dirty_nobuffers);
/*
+ * Call this whenever redirtying a page, to de-account the dirty counters
+ * (NR_DIRTIED, BDI_DIRTIED, tsk->nr_dirtied), so that they match the written
+ * counters (NR_WRITTEN, BDI_WRITTEN) in long term. The mismatches will lead to
+ * systematic errors in balanced_dirty_ratelimit and the dirty pages position
+ * control.
+ */
+void account_page_redirty(struct page *page)
+{
+ struct address_space *mapping = page->mapping;
+ if (mapping && mapping_cap_account_dirty(mapping)) {
+ current->nr_dirtied--;
+ dec_zone_page_state(page, NR_DIRTIED);
+ dec_bdi_stat(mapping->backing_dev_info, BDI_DIRTIED);
+ }
+}
+EXPORT_SYMBOL(account_page_redirty);
+
+/*
* When a writepage implementation decides that it doesn't want to write this
* page for some reason, it should redirty the locked page via
* redirty_page_for_writepage() and it should then unlock the page and return 0
@@ -1890,6 +2025,7 @@
int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page)
{
wbc->pages_skipped++;
+ account_page_redirty(page);
return __set_page_dirty_nobuffers(page);
}
EXPORT_SYMBOL(redirty_page_for_writepage);
