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yaml
---
r: 274359
b: refs/heads/master
c: 143dfe8
h: refs/heads/master
i:
  274357: 09cc3db
  274355: 20a6930
  274351: 163ace8
v: v3
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Wu Fengguang committed Oct 3, 2011
1 parent e6aa646 commit fcd09d5
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Showing 3 changed files with 57 additions and 130 deletions.
2 changes: 1 addition & 1 deletion [refs]
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Original file line number Diff line number Diff line change
@@ -1,2 +1,2 @@
---
refs/heads/master: 9d823e8f6b1b7b39f952d7d1795f29162143a433
refs/heads/master: 143dfe8611a63030ce0c79419dc362f7838be557
24 changes: 0 additions & 24 deletions trunk/include/trace/events/writeback.h
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Original file line number Diff line number Diff line change
Expand Up @@ -104,30 +104,6 @@ DEFINE_WRITEBACK_EVENT(writeback_bdi_register);
DEFINE_WRITEBACK_EVENT(writeback_bdi_unregister);
DEFINE_WRITEBACK_EVENT(writeback_thread_start);
DEFINE_WRITEBACK_EVENT(writeback_thread_stop);
DEFINE_WRITEBACK_EVENT(balance_dirty_start);
DEFINE_WRITEBACK_EVENT(balance_dirty_wait);

TRACE_EVENT(balance_dirty_written,

TP_PROTO(struct backing_dev_info *bdi, int written),

TP_ARGS(bdi, written),

TP_STRUCT__entry(
__array(char, name, 32)
__field(int, written)
),

TP_fast_assign(
strncpy(__entry->name, dev_name(bdi->dev), 32);
__entry->written = written;
),

TP_printk("bdi %s written %d",
__entry->name,
__entry->written
)
);

DECLARE_EVENT_CLASS(wbc_class,
TP_PROTO(struct writeback_control *wbc, struct backing_dev_info *bdi),
Expand Down
161 changes: 56 additions & 105 deletions trunk/mm/page-writeback.c
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Original file line number Diff line number Diff line change
Expand Up @@ -250,50 +250,6 @@ static void bdi_writeout_fraction(struct backing_dev_info *bdi,
numerator, denominator);
}

static inline void task_dirties_fraction(struct task_struct *tsk,
long *numerator, long *denominator)
{
prop_fraction_single(&vm_dirties, &tsk->dirties,
numerator, denominator);
}

/*
* task_dirty_limit - scale down dirty throttling threshold for one task
*
* task specific dirty limit:
*
* dirty -= (dirty/8) * p_{t}
*
* To protect light/slow dirtying tasks from heavier/fast ones, we start
* throttling individual tasks before reaching the bdi dirty limit.
* Relatively low thresholds will be allocated to heavy dirtiers. So when
* dirty pages grow large, heavy dirtiers will be throttled first, which will
* 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 / TASK_LIMIT_FRACTION;

task_dirties_fraction(tsk, &numerator, &denominator);
inv *= numerator;
do_div(inv, denominator);

dirty -= inv;

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;
}

/*
*
*/
Expand Down Expand Up @@ -986,30 +942,36 @@ static unsigned long dirty_poll_interval(unsigned long dirty,
/*
* 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
* the caller to perform writeback if the system is over `vm_dirty_ratio'.
* the caller to wait once crossing the (background_thresh + dirty_thresh) / 2.
* If we're over `background_thresh' then the writeback threads are woken to
* perform some writeout.
*/
static void balance_dirty_pages(struct address_space *mapping,
unsigned long write_chunk)
unsigned long pages_dirtied)
{
unsigned long nr_reclaimable, bdi_nr_reclaimable;
unsigned long nr_reclaimable; /* = file_dirty + unstable_nfs */
unsigned long bdi_reclaimable;
unsigned long nr_dirty; /* = file_dirty + writeback + unstable_nfs */
unsigned long bdi_dirty;
unsigned long freerun;
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;
long pause = 0;
bool dirty_exceeded = false;
bool clear_dirty_exceeded = true;
unsigned long task_ratelimit;
unsigned long dirty_ratelimit;
unsigned long pos_ratio;
struct backing_dev_info *bdi = mapping->backing_dev_info;
unsigned long start_time = jiffies;

for (;;) {
/*
* Unstable writes are a feature of certain networked
* filesystems (i.e. NFS) in which data may have been
* written to the server's write cache, but has not yet
* been flushed to permanent storage.
*/
nr_reclaimable = global_page_state(NR_FILE_DIRTY) +
global_page_state(NR_UNSTABLE_NFS);
nr_dirty = nr_reclaimable + global_page_state(NR_WRITEBACK);
Expand All @@ -1026,9 +988,23 @@ static void balance_dirty_pages(struct address_space *mapping,
if (nr_dirty <= freerun)
break;

if (unlikely(!writeback_in_progress(bdi)))
bdi_start_background_writeback(bdi);

/*
* bdi_thresh is not treated as some limiting factor as
* dirty_thresh, due to reasons
* - in JBOD setup, bdi_thresh can fluctuate a lot
* - in a system with HDD and USB key, the USB key may somehow
* go into state (bdi_dirty >> bdi_thresh) either because
* bdi_dirty starts high, or because bdi_thresh drops low.
* In this case we don't want to hard throttle the USB key
* dirtiers for 100 seconds until bdi_dirty drops under
* bdi_thresh. Instead the auxiliary bdi control line in
* bdi_position_ratio() will let the dirtier task progress
* at some rate <= (write_bw / 2) for bringing down bdi_dirty.
*/
bdi_thresh = bdi_dirty_limit(bdi, dirty_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
Expand All @@ -1040,57 +1016,41 @@ static void balance_dirty_pages(struct address_space *mapping,
* actually dirty; with m+n sitting in the percpu
* deltas.
*/
if (task_bdi_thresh < 2 * bdi_stat_error(bdi)) {
bdi_nr_reclaimable = bdi_stat_sum(bdi, BDI_RECLAIMABLE);
bdi_dirty = bdi_nr_reclaimable +
if (bdi_thresh < 2 * bdi_stat_error(bdi)) {
bdi_reclaimable = bdi_stat_sum(bdi, BDI_RECLAIMABLE);
bdi_dirty = bdi_reclaimable +
bdi_stat_sum(bdi, BDI_WRITEBACK);
} else {
bdi_nr_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE);
bdi_dirty = bdi_nr_reclaimable +
bdi_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE);
bdi_dirty = bdi_reclaimable +
bdi_stat(bdi, BDI_WRITEBACK);
}

/*
* 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_dirty > task_bdi_thresh) ||
dirty_exceeded = (bdi_dirty > bdi_thresh) ||
(nr_dirty > dirty_thresh);
clear_dirty_exceeded = (bdi_dirty <= min_task_bdi_thresh) &&
(nr_dirty <= dirty_thresh);

if (!dirty_exceeded)
break;

if (!bdi->dirty_exceeded)
if (dirty_exceeded && !bdi->dirty_exceeded)
bdi->dirty_exceeded = 1;

bdi_update_bandwidth(bdi, dirty_thresh, background_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
* written to the server's write cache, but has not yet
* been flushed to permanent storage.
* Only move pages to writeback if this bdi is over its
* threshold otherwise wait until the disk writes catch
* up.
*/
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 */
dirty_ratelimit = bdi->dirty_ratelimit;
pos_ratio = bdi_position_ratio(bdi, dirty_thresh,
background_thresh, nr_dirty,
bdi_thresh, bdi_dirty);
if (unlikely(pos_ratio == 0)) {
pause = MAX_PAUSE;
goto pause;
}
task_ratelimit = (u64)dirty_ratelimit *
pos_ratio >> RATELIMIT_CALC_SHIFT;
pause = (HZ * pages_dirtied) / (task_ratelimit | 1);
pause = min_t(long, pause, MAX_PAUSE);

pause:
__set_current_state(TASK_UNINTERRUPTIBLE);
io_schedule_timeout(pause);
trace_balance_dirty_wait(bdi);

dirty_thresh = hard_dirty_limit(dirty_thresh);
/*
Expand All @@ -1099,22 +1059,11 @@ static void balance_dirty_pages(struct address_space *mapping,
* 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 &&
bdi_dirty < (task_bdi_thresh + bdi_thresh) / 2 &&
time_after(jiffies, start_time + MAX_PAUSE))
if (nr_dirty < dirty_thresh)
break;

/*
* Increase the delay for each loop, up to our previous
* default of taking a 100ms nap.
*/
pause <<= 1;
if (pause > HZ / 10)
pause = HZ / 10;
}

/* Clear dirty_exceeded flag only when no task can exceed the limit */
if (clear_dirty_exceeded && bdi->dirty_exceeded)
if (!dirty_exceeded && bdi->dirty_exceeded)
bdi->dirty_exceeded = 0;

current->nr_dirtied = 0;
Expand All @@ -1131,8 +1080,10 @@ static void balance_dirty_pages(struct address_space *mapping,
* In normal mode, we start background writeout at the lower
* background_thresh, to keep the amount of dirty memory low.
*/
if ((laptop_mode && pages_written) ||
(!laptop_mode && (nr_reclaimable > background_thresh)))
if (laptop_mode)
return;

if (nr_reclaimable > background_thresh)
bdi_start_background_writeback(bdi);
}

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