unsigned int for_kupdate:1;
unsigned int range_cyclic:1;
unsigned int for_background:1;
+ enum wb_reason reason; /* why was writeback initiated? */
struct list_head list; /* pending work list */
struct completion *done; /* set if the caller waits */
};
+const char *wb_reason_name[] = {
+ [WB_REASON_BACKGROUND] = "background",
+ [WB_REASON_TRY_TO_FREE_PAGES] = "try_to_free_pages",
+ [WB_REASON_SYNC] = "sync",
+ [WB_REASON_PERIODIC] = "periodic",
+ [WB_REASON_LAPTOP_TIMER] = "laptop_timer",
+ [WB_REASON_FREE_MORE_MEM] = "free_more_memory",
+ [WB_REASON_FS_FREE_SPACE] = "fs_free_space",
+ [WB_REASON_FORKER_THREAD] = "forker_thread"
+};
+
/*
* Include the creation of the trace points after defining the
* wb_writeback_work structure so that the definition remains local to this
static void
__bdi_start_writeback(struct backing_dev_info *bdi, long nr_pages,
- bool range_cyclic)
+ bool range_cyclic, enum wb_reason reason)
{
struct wb_writeback_work *work;
work->sync_mode = WB_SYNC_NONE;
work->nr_pages = nr_pages;
work->range_cyclic = range_cyclic;
+ work->reason = reason;
bdi_queue_work(bdi, work);
}
* completion. Caller need not hold sb s_umount semaphore.
*
*/
-void bdi_start_writeback(struct backing_dev_info *bdi, long nr_pages)
+void bdi_start_writeback(struct backing_dev_info *bdi, long nr_pages,
+ enum wb_reason reason)
{
- __bdi_start_writeback(bdi, nr_pages, true);
+ __bdi_start_writeback(bdi, nr_pages, true, reason);
}
/**
*/
static int move_expired_inodes(struct list_head *delaying_queue,
struct list_head *dispatch_queue,
- unsigned long *older_than_this)
+ struct wb_writeback_work *work)
{
LIST_HEAD(tmp);
struct list_head *pos, *node;
while (!list_empty(delaying_queue)) {
inode = wb_inode(delaying_queue->prev);
- if (older_than_this &&
- inode_dirtied_after(inode, *older_than_this))
+ if (work->older_than_this &&
+ inode_dirtied_after(inode, *work->older_than_this))
break;
if (sb && sb != inode->i_sb)
do_sb_sort = 1;
* |
* +--> dequeue for IO
*/
-static void queue_io(struct bdi_writeback *wb, unsigned long *older_than_this)
+static void queue_io(struct bdi_writeback *wb, struct wb_writeback_work *work)
{
int moved;
assert_spin_locked(&wb->list_lock);
list_splice_init(&wb->b_more_io, &wb->b_io);
- moved = move_expired_inodes(&wb->b_dirty, &wb->b_io, older_than_this);
- trace_writeback_queue_io(wb, older_than_this, moved);
+ moved = move_expired_inodes(&wb->b_dirty, &wb->b_io, work);
+ trace_writeback_queue_io(wb, work, moved);
}
static int write_inode(struct inode *inode, struct writeback_control *wbc)
return wrote;
}
-long writeback_inodes_wb(struct bdi_writeback *wb, long nr_pages)
+long writeback_inodes_wb(struct bdi_writeback *wb, long nr_pages,
+ enum wb_reason reason)
{
struct wb_writeback_work work = {
.nr_pages = nr_pages,
.sync_mode = WB_SYNC_NONE,
.range_cyclic = 1,
+ .reason = reason,
};
spin_lock(&wb->list_lock);
if (list_empty(&wb->b_io))
- queue_io(wb, NULL);
+ queue_io(wb, &work);
__writeback_inodes_wb(wb, &work);
spin_unlock(&wb->list_lock);
return nr_pages - work.nr_pages;
}
-static inline bool over_bground_thresh(void)
+static bool over_bground_thresh(struct backing_dev_info *bdi)
{
unsigned long background_thresh, dirty_thresh;
global_dirty_limits(&background_thresh, &dirty_thresh);
- return (global_page_state(NR_FILE_DIRTY) +
- global_page_state(NR_UNSTABLE_NFS) > background_thresh);
+ if (global_page_state(NR_FILE_DIRTY) +
+ global_page_state(NR_UNSTABLE_NFS) > background_thresh)
+ return true;
+
+ if (bdi_stat(bdi, BDI_RECLAIMABLE) >
+ bdi_dirty_limit(bdi, background_thresh))
+ return true;
+
+ return false;
}
/*
static void wb_update_bandwidth(struct bdi_writeback *wb,
unsigned long start_time)
{
- __bdi_update_bandwidth(wb->bdi, 0, 0, 0, 0, start_time);
+ __bdi_update_bandwidth(wb->bdi, 0, 0, 0, 0, 0, start_time);
}
/*
* For background writeout, stop when we are below the
* background dirty threshold
*/
- if (work->for_background && !over_bground_thresh())
+ if (work->for_background && !over_bground_thresh(wb->bdi))
break;
if (work->for_kupdate) {
trace_writeback_start(wb->bdi, work);
if (list_empty(&wb->b_io))
- queue_io(wb, work->older_than_this);
+ queue_io(wb, work);
if (work->sb)
progress = writeback_sb_inodes(work->sb, wb, work);
else
static long wb_check_background_flush(struct bdi_writeback *wb)
{
- if (over_bground_thresh()) {
+ if (over_bground_thresh(wb->bdi)) {
struct wb_writeback_work work = {
.nr_pages = LONG_MAX,
.sync_mode = WB_SYNC_NONE,
.for_background = 1,
.range_cyclic = 1,
+ .reason = WB_REASON_BACKGROUND,
};
return wb_writeback(wb, &work);
.sync_mode = WB_SYNC_NONE,
.for_kupdate = 1,
.range_cyclic = 1,
+ .reason = WB_REASON_PERIODIC,
};
return wb_writeback(wb, &work);
* Start writeback of `nr_pages' pages. If `nr_pages' is zero, write back
* the whole world.
*/
-void wakeup_flusher_threads(long nr_pages)
+void wakeup_flusher_threads(long nr_pages, enum wb_reason reason)
{
struct backing_dev_info *bdi;
list_for_each_entry_rcu(bdi, &bdi_list, bdi_list) {
if (!bdi_has_dirty_io(bdi))
continue;
- __bdi_start_writeback(bdi, nr_pages, false);
+ __bdi_start_writeback(bdi, nr_pages, false, reason);
}
rcu_read_unlock();
}
* on how many (if any) will be written, and this function does not wait
* for IO completion of submitted IO.
*/
-void writeback_inodes_sb_nr(struct super_block *sb, unsigned long nr)
+void writeback_inodes_sb_nr(struct super_block *sb,
+ unsigned long nr,
+ enum wb_reason reason)
{
DECLARE_COMPLETION_ONSTACK(done);
struct wb_writeback_work work = {
.tagged_writepages = 1,
.done = &done,
.nr_pages = nr,
+ .reason = reason,
};
WARN_ON(!rwsem_is_locked(&sb->s_umount));
* on how many (if any) will be written, and this function does not wait
* for IO completion of submitted IO.
*/
-void writeback_inodes_sb(struct super_block *sb)
+void writeback_inodes_sb(struct super_block *sb, enum wb_reason reason)
{
- return writeback_inodes_sb_nr(sb, get_nr_dirty_pages());
+ return writeback_inodes_sb_nr(sb, get_nr_dirty_pages(), reason);
}
EXPORT_SYMBOL(writeback_inodes_sb);
* Invoke writeback_inodes_sb if no writeback is currently underway.
* Returns 1 if writeback was started, 0 if not.
*/
-int writeback_inodes_sb_if_idle(struct super_block *sb)
+int writeback_inodes_sb_if_idle(struct super_block *sb, enum wb_reason reason)
{
if (!writeback_in_progress(sb->s_bdi)) {
down_read(&sb->s_umount);
- writeback_inodes_sb(sb);
+ writeback_inodes_sb(sb, reason);
up_read(&sb->s_umount);
return 1;
} else
* Returns 1 if writeback was started, 0 if not.
*/
int writeback_inodes_sb_nr_if_idle(struct super_block *sb,
- unsigned long nr)
+ unsigned long nr,
+ enum wb_reason reason)
{
if (!writeback_in_progress(sb->s_bdi)) {
down_read(&sb->s_umount);
- writeback_inodes_sb_nr(sb, nr);
+ writeback_inodes_sb_nr(sb, nr, reason);
up_read(&sb->s_umount);
return 1;
} else
.nr_pages = LONG_MAX,
.range_cyclic = 0,
.done = &done,
+ .reason = WB_REASON_SYNC,
};
WARN_ON(!rwsem_is_locked(&sb->s_umount));
__field(int, for_kupdate)
__field(int, range_cyclic)
__field(int, for_background)
+ __field(int, reason)
),
TP_fast_assign(
strncpy(__entry->name, dev_name(bdi->dev), 32);
__entry->for_kupdate = work->for_kupdate;
__entry->range_cyclic = work->range_cyclic;
__entry->for_background = work->for_background;
+ __entry->reason = work->reason;
),
TP_printk("bdi %s: sb_dev %d:%d nr_pages=%ld sync_mode=%d "
- "kupdate=%d range_cyclic=%d background=%d",
+ "kupdate=%d range_cyclic=%d background=%d reason=%s",
__entry->name,
MAJOR(__entry->sb_dev), MINOR(__entry->sb_dev),
__entry->nr_pages,
__entry->sync_mode,
__entry->for_kupdate,
__entry->range_cyclic,
- __entry->for_background
+ __entry->for_background,
+ wb_reason_name[__entry->reason]
)
);
#define DEFINE_WRITEBACK_WORK_EVENT(name) \
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),
TRACE_EVENT(writeback_queue_io,
TP_PROTO(struct bdi_writeback *wb,
- unsigned long *older_than_this,
+ struct wb_writeback_work *work,
int moved),
- TP_ARGS(wb, older_than_this, moved),
+ TP_ARGS(wb, work, moved),
TP_STRUCT__entry(
__array(char, name, 32)
__field(unsigned long, older)
__field(long, age)
__field(int, moved)
+ __field(int, reason)
),
TP_fast_assign(
+ unsigned long *older_than_this = work->older_than_this;
strncpy(__entry->name, dev_name(wb->bdi->dev), 32);
__entry->older = older_than_this ? *older_than_this : 0;
__entry->age = older_than_this ?
(jiffies - *older_than_this) * 1000 / HZ : -1;
__entry->moved = moved;
+ __entry->reason = work->reason;
),
- TP_printk("bdi %s: older=%lu age=%ld enqueue=%d",
+ TP_printk("bdi %s: older=%lu age=%ld enqueue=%d reason=%s",
__entry->name,
__entry->older, /* older_than_this in jiffies */
__entry->age, /* older_than_this in relative milliseconds */
- __entry->moved)
+ __entry->moved,
+ wb_reason_name[__entry->reason])
);
TRACE_EVENT(global_dirty_state,
)
);
+#define KBps(x) ((x) << (PAGE_SHIFT - 10))
+
+TRACE_EVENT(bdi_dirty_ratelimit,
+
+ TP_PROTO(struct backing_dev_info *bdi,
+ unsigned long dirty_rate,
+ unsigned long task_ratelimit),
+
+ TP_ARGS(bdi, dirty_rate, task_ratelimit),
+
+ TP_STRUCT__entry(
+ __array(char, bdi, 32)
+ __field(unsigned long, write_bw)
+ __field(unsigned long, avg_write_bw)
+ __field(unsigned long, dirty_rate)
+ __field(unsigned long, dirty_ratelimit)
+ __field(unsigned long, task_ratelimit)
+ __field(unsigned long, balanced_dirty_ratelimit)
+ ),
+
+ TP_fast_assign(
+ strlcpy(__entry->bdi, dev_name(bdi->dev), 32);
+ __entry->write_bw = KBps(bdi->write_bandwidth);
+ __entry->avg_write_bw = KBps(bdi->avg_write_bandwidth);
+ __entry->dirty_rate = KBps(dirty_rate);
+ __entry->dirty_ratelimit = KBps(bdi->dirty_ratelimit);
+ __entry->task_ratelimit = KBps(task_ratelimit);
+ __entry->balanced_dirty_ratelimit =
+ KBps(bdi->balanced_dirty_ratelimit);
+ ),
+
+ TP_printk("bdi %s: "
+ "write_bw=%lu awrite_bw=%lu dirty_rate=%lu "
+ "dirty_ratelimit=%lu task_ratelimit=%lu "
+ "balanced_dirty_ratelimit=%lu",
+ __entry->bdi,
+ __entry->write_bw, /* write bandwidth */
+ __entry->avg_write_bw, /* avg write bandwidth */
+ __entry->dirty_rate, /* bdi dirty rate */
+ __entry->dirty_ratelimit, /* base ratelimit */
+ __entry->task_ratelimit, /* ratelimit with position control */
+ __entry->balanced_dirty_ratelimit /* the balanced ratelimit */
+ )
+);
+
+TRACE_EVENT(balance_dirty_pages,
+
+ TP_PROTO(struct backing_dev_info *bdi,
+ unsigned long thresh,
+ unsigned long bg_thresh,
+ unsigned long dirty,
+ unsigned long bdi_thresh,
+ unsigned long bdi_dirty,
+ unsigned long dirty_ratelimit,
+ unsigned long task_ratelimit,
+ unsigned long dirtied,
+ 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),
+
+ TP_STRUCT__entry(
+ __array( char, bdi, 32)
+ __field(unsigned long, limit)
+ __field(unsigned long, setpoint)
+ __field(unsigned long, dirty)
+ __field(unsigned long, bdi_setpoint)
+ __field(unsigned long, bdi_dirty)
+ __field(unsigned long, dirty_ratelimit)
+ __field(unsigned long, task_ratelimit)
+ __field(unsigned int, dirtied)
+ __field(unsigned int, dirtied_pause)
+ __field(unsigned long, paused)
+ __field( long, pause)
+ ),
+
+ TP_fast_assign(
+ unsigned long freerun = (thresh + bg_thresh) / 2;
+ strlcpy(__entry->bdi, dev_name(bdi->dev), 32);
+
+ __entry->limit = global_dirty_limit;
+ __entry->setpoint = (global_dirty_limit + freerun) / 2;
+ __entry->dirty = dirty;
+ __entry->bdi_setpoint = __entry->setpoint *
+ bdi_thresh / (thresh + 1);
+ __entry->bdi_dirty = bdi_dirty;
+ __entry->dirty_ratelimit = KBps(dirty_ratelimit);
+ __entry->task_ratelimit = KBps(task_ratelimit);
+ __entry->dirtied = dirtied;
+ __entry->dirtied_pause = current->nr_dirtied_pause;
+ __entry->pause = pause * 1000 / HZ;
+ __entry->paused = (jiffies - start_time) * 1000 / HZ;
+ ),
+
+
+ TP_printk("bdi %s: "
+ "limit=%lu setpoint=%lu dirty=%lu "
+ "bdi_setpoint=%lu bdi_dirty=%lu "
+ "dirty_ratelimit=%lu task_ratelimit=%lu "
+ "dirtied=%u dirtied_pause=%u "
+ "paused=%lu pause=%ld",
+ __entry->bdi,
+ __entry->limit,
+ __entry->setpoint,
+ __entry->dirty,
+ __entry->bdi_setpoint,
+ __entry->bdi_dirty,
+ __entry->dirty_ratelimit,
+ __entry->task_ratelimit,
+ __entry->dirtied,
+ __entry->dirtied_pause,
+ __entry->paused, /* ms */
+ __entry->pause /* ms */
+ )
+);
+
DECLARE_EVENT_CLASS(writeback_congest_waited_template,
TP_PROTO(unsigned int usec_timeout, unsigned int usec_delayed),
*/
#define BANDWIDTH_INTERVAL max(HZ/5, 1)
+#define RATELIMIT_CALC_SHIFT 10
+
/*
* After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited
* will look to see if it needs to force writeback or throttling.
*/
static long ratelimit_pages = 32;
-/*
- * When balance_dirty_pages decides that the caller needs to perform some
- * non-background writeback, this is how many pages it will attempt to write.
- * It should be somewhat larger than dirtied pages to ensure that reasonably
- * large amounts of I/O are submitted.
- */
-static inline long sync_writeback_pages(unsigned long dirtied)
-{
- if (dirtied < ratelimit_pages)
- dirtied = ratelimit_pages;
-
- return dirtied + dirtied / 2;
-}
-
/* The following parameters are exported via /proc/sys/vm */
/*
int shift = calc_period_shift();
prop_change_shift(&vm_completions, shift);
prop_change_shift(&vm_dirties, shift);
+
+ writeback_set_ratelimit();
}
int dirty_background_ratio_handler(struct ctl_table *table, int write,
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;
-}
-
/*
* bdi_min_ratio keeps the sum of the minimum dirty shares of all
* registered backing devices, which, for obvious reasons, can not
return x + 1; /* Ensure that we never return 0 */
}
+static unsigned long dirty_freerun_ceiling(unsigned long thresh,
+ unsigned long bg_thresh)
+{
+ return (thresh + bg_thresh) / 2;
+}
+
static unsigned long hard_dirty_limit(unsigned long thresh)
{
return max(thresh, global_dirty_limit);
return bdi_dirty;
}
+/*
+ * Dirty position control.
+ *
+ * (o) global/bdi setpoints
+ *
+ * We want the dirty pages be balanced around the global/bdi setpoints.
+ * When the number of dirty pages is higher/lower than the setpoint, the
+ * dirty position control ratio (and hence task dirty ratelimit) will be
+ * decreased/increased to bring the dirty pages back to the setpoint.
+ *
+ * pos_ratio = 1 << RATELIMIT_CALC_SHIFT
+ *
+ * if (dirty < setpoint) scale up pos_ratio
+ * if (dirty > setpoint) scale down pos_ratio
+ *
+ * if (bdi_dirty < bdi_setpoint) scale up pos_ratio
+ * if (bdi_dirty > bdi_setpoint) scale down pos_ratio
+ *
+ * task_ratelimit = dirty_ratelimit * pos_ratio >> RATELIMIT_CALC_SHIFT
+ *
+ * (o) global control line
+ *
+ * ^ pos_ratio
+ * |
+ * | |<===== global dirty control scope ======>|
+ * 2.0 .............*
+ * | .*
+ * | . *
+ * | . *
+ * | . *
+ * | . *
+ * | . *
+ * 1.0 ................................*
+ * | . . *
+ * | . . *
+ * | . . *
+ * | . . *
+ * | . . *
+ * 0 +------------.------------------.----------------------*------------->
+ * freerun^ setpoint^ limit^ dirty pages
+ *
+ * (o) bdi control line
+ *
+ * ^ pos_ratio
+ * |
+ * | *
+ * | *
+ * | *
+ * | *
+ * | * |<=========== span ============>|
+ * 1.0 .......................*
+ * | . *
+ * | . *
+ * | . *
+ * | . *
+ * | . *
+ * | . *
+ * | . *
+ * | . *
+ * | . *
+ * | . *
+ * | . *
+ * 1/4 ...............................................* * * * * * * * * * * *
+ * | . .
+ * | . .
+ * | . .
+ * 0 +----------------------.-------------------------------.------------->
+ * bdi_setpoint^ x_intercept^
+ *
+ * The bdi control line won't drop below pos_ratio=1/4, so that bdi_dirty can
+ * be smoothly throttled down to normal if it starts high in situations like
+ * - start writing to a slow SD card and a fast disk at the same time. The SD
+ * card's bdi_dirty may rush to many times higher than bdi_setpoint.
+ * - the bdi dirty thresh drops quickly due to change of JBOD workload
+ */
+static unsigned long bdi_position_ratio(struct backing_dev_info *bdi,
+ unsigned long thresh,
+ unsigned long bg_thresh,
+ unsigned long dirty,
+ unsigned long bdi_thresh,
+ unsigned long bdi_dirty)
+{
+ unsigned long write_bw = bdi->avg_write_bandwidth;
+ unsigned long freerun = dirty_freerun_ceiling(thresh, bg_thresh);
+ unsigned long limit = hard_dirty_limit(thresh);
+ unsigned long x_intercept;
+ unsigned long setpoint; /* dirty pages' target balance point */
+ unsigned long bdi_setpoint;
+ unsigned long span;
+ long long pos_ratio; /* for scaling up/down the rate limit */
+ long x;
+
+ if (unlikely(dirty >= limit))
+ return 0;
+
+ /*
+ * global setpoint
+ *
+ * setpoint - dirty 3
+ * f(dirty) := 1.0 + (----------------)
+ * limit - setpoint
+ *
+ * it's a 3rd order polynomial that subjects to
+ *
+ * (1) f(freerun) = 2.0 => rampup dirty_ratelimit reasonably fast
+ * (2) f(setpoint) = 1.0 => the balance point
+ * (3) f(limit) = 0 => the hard limit
+ * (4) df/dx <= 0 => negative feedback control
+ * (5) the closer to setpoint, the smaller |df/dx| (and the reverse)
+ * => fast response on large errors; small oscillation near setpoint
+ */
+ setpoint = (freerun + limit) / 2;
+ x = div_s64((setpoint - dirty) << RATELIMIT_CALC_SHIFT,
+ limit - setpoint + 1);
+ pos_ratio = x;
+ pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
+ pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
+ pos_ratio += 1 << RATELIMIT_CALC_SHIFT;
+
+ /*
+ * We have computed basic pos_ratio above based on global situation. If
+ * the bdi is over/under its share of dirty pages, we want to scale
+ * pos_ratio further down/up. That is done by the following mechanism.
+ */
+
+ /*
+ * bdi setpoint
+ *
+ * f(bdi_dirty) := 1.0 + k * (bdi_dirty - bdi_setpoint)
+ *
+ * x_intercept - bdi_dirty
+ * := --------------------------
+ * x_intercept - bdi_setpoint
+ *
+ * The main bdi control line is a linear function that subjects to
+ *
+ * (1) f(bdi_setpoint) = 1.0
+ * (2) k = - 1 / (8 * write_bw) (in single bdi case)
+ * or equally: x_intercept = bdi_setpoint + 8 * write_bw
+ *
+ * For single bdi case, the dirty pages are observed to fluctuate
+ * regularly within range
+ * [bdi_setpoint - write_bw/2, bdi_setpoint + write_bw/2]
+ * for various filesystems, where (2) can yield in a reasonable 12.5%
+ * fluctuation range for pos_ratio.
+ *
+ * For JBOD case, bdi_thresh (not bdi_dirty!) could fluctuate up to its
+ * own size, so move the slope over accordingly and choose a slope that
+ * yields 100% pos_ratio fluctuation on suddenly doubled bdi_thresh.
+ */
+ if (unlikely(bdi_thresh > thresh))
+ bdi_thresh = thresh;
+ bdi_thresh = max(bdi_thresh, (limit - dirty) / 8);
+ /*
+ * scale global setpoint to bdi's:
+ * bdi_setpoint = setpoint * bdi_thresh / thresh
+ */
+ x = div_u64((u64)bdi_thresh << 16, thresh + 1);
+ bdi_setpoint = setpoint * (u64)x >> 16;
+ /*
+ * Use span=(8*write_bw) in single bdi case as indicated by
+ * (thresh - bdi_thresh ~= 0) and transit to bdi_thresh in JBOD case.
+ *
+ * bdi_thresh thresh - bdi_thresh
+ * span = ---------- * (8 * write_bw) + ------------------- * bdi_thresh
+ * thresh thresh
+ */
+ span = (thresh - bdi_thresh + 8 * write_bw) * (u64)x >> 16;
+ x_intercept = bdi_setpoint + span;
+
+ if (bdi_dirty < x_intercept - span / 4) {
+ pos_ratio = div_u64(pos_ratio * (x_intercept - bdi_dirty),
+ x_intercept - bdi_setpoint + 1);
+ } else
+ pos_ratio /= 4;
+
+ /*
+ * bdi reserve area, safeguard against dirty pool underrun and disk idle
+ * It may push the desired control point of global dirty pages higher
+ * than setpoint.
+ */
+ x_intercept = bdi_thresh / 2;
+ if (bdi_dirty < x_intercept) {
+ if (bdi_dirty > x_intercept / 8)
+ pos_ratio = div_u64(pos_ratio * x_intercept, bdi_dirty);
+ else
+ pos_ratio *= 8;
+ }
+
+ return pos_ratio;
+}
+
static void bdi_update_write_bandwidth(struct backing_dev_info *bdi,
unsigned long elapsed,
unsigned long written)
spin_unlock(&dirty_lock);
}
+/*
+ * Maintain bdi->dirty_ratelimit, the base dirty throttle rate.
+ *
+ * Normal bdi tasks will be curbed at or below it in long term.
+ * Obviously it should be around (write_bw / N) when there are N dd tasks.
+ */
+static void bdi_update_dirty_ratelimit(struct backing_dev_info *bdi,
+ unsigned long thresh,
+ unsigned long bg_thresh,
+ unsigned long dirty,
+ unsigned long bdi_thresh,
+ unsigned long bdi_dirty,
+ unsigned long dirtied,
+ unsigned long elapsed)
+{
+ unsigned long freerun = dirty_freerun_ceiling(thresh, bg_thresh);
+ unsigned long limit = hard_dirty_limit(thresh);
+ unsigned long setpoint = (freerun + limit) / 2;
+ unsigned long write_bw = bdi->avg_write_bandwidth;
+ unsigned long dirty_ratelimit = bdi->dirty_ratelimit;
+ unsigned long dirty_rate;
+ unsigned long task_ratelimit;
+ unsigned long balanced_dirty_ratelimit;
+ unsigned long pos_ratio;
+ unsigned long step;
+ unsigned long x;
+
+ /*
+ * The dirty rate will match the writeout rate in long term, except
+ * when dirty pages are truncated by userspace or re-dirtied by FS.
+ */
+ dirty_rate = (dirtied - bdi->dirtied_stamp) * HZ / elapsed;
+
+ pos_ratio = bdi_position_ratio(bdi, thresh, bg_thresh, dirty,
+ bdi_thresh, bdi_dirty);
+ /*
+ * task_ratelimit reflects each dd's dirty rate for the past 200ms.
+ */
+ task_ratelimit = (u64)dirty_ratelimit *
+ pos_ratio >> RATELIMIT_CALC_SHIFT;
+ task_ratelimit++; /* it helps rampup dirty_ratelimit from tiny values */
+
+ /*
+ * A linear estimation of the "balanced" throttle rate. The theory is,
+ * if there are N dd tasks, each throttled at task_ratelimit, the bdi's
+ * dirty_rate will be measured to be (N * task_ratelimit). So the below
+ * formula will yield the balanced rate limit (write_bw / N).
+ *
+ * Note that the expanded form is not a pure rate feedback:
+ * rate_(i+1) = rate_(i) * (write_bw / dirty_rate) (1)
+ * but also takes pos_ratio into account:
+ * rate_(i+1) = rate_(i) * (write_bw / dirty_rate) * pos_ratio (2)
+ *
+ * (1) is not realistic because pos_ratio also takes part in balancing
+ * the dirty rate. Consider the state
+ * pos_ratio = 0.5 (3)
+ * rate = 2 * (write_bw / N) (4)
+ * If (1) is used, it will stuck in that state! Because each dd will
+ * be throttled at
+ * task_ratelimit = pos_ratio * rate = (write_bw / N) (5)
+ * yielding
+ * dirty_rate = N * task_ratelimit = write_bw (6)
+ * put (6) into (1) we get
+ * rate_(i+1) = rate_(i) (7)
+ *
+ * So we end up using (2) to always keep
+ * rate_(i+1) ~= (write_bw / N) (8)
+ * regardless of the value of pos_ratio. As long as (8) is satisfied,
+ * pos_ratio is able to drive itself to 1.0, which is not only where
+ * the dirty count meet the setpoint, but also where the slope of
+ * pos_ratio is most flat and hence task_ratelimit is least fluctuated.
+ */
+ balanced_dirty_ratelimit = div_u64((u64)task_ratelimit * write_bw,
+ dirty_rate | 1);
+
+ /*
+ * We could safely do this and return immediately:
+ *
+ * bdi->dirty_ratelimit = balanced_dirty_ratelimit;
+ *
+ * However to get a more stable dirty_ratelimit, the below elaborated
+ * code makes use of task_ratelimit to filter out sigular points and
+ * limit the step size.
+ *
+ * The below code essentially only uses the relative value of
+ *
+ * task_ratelimit - dirty_ratelimit
+ * = (pos_ratio - 1) * dirty_ratelimit
+ *
+ * which reflects the direction and size of dirty position error.
+ */
+
+ /*
+ * dirty_ratelimit will follow balanced_dirty_ratelimit iff
+ * task_ratelimit is on the same side of dirty_ratelimit, too.
+ * For example, when
+ * - dirty_ratelimit > balanced_dirty_ratelimit
+ * - dirty_ratelimit > task_ratelimit (dirty pages are above setpoint)
+ * lowering dirty_ratelimit will help meet both the position and rate
+ * control targets. Otherwise, don't update dirty_ratelimit if it will
+ * only help meet the rate target. After all, what the users ultimately
+ * feel and care are stable dirty rate and small position error.
+ *
+ * |task_ratelimit - dirty_ratelimit| is used to limit the step size
+ * and filter out the sigular points of balanced_dirty_ratelimit. Which
+ * keeps jumping around randomly and can even leap far away at times
+ * due to the small 200ms estimation period of dirty_rate (we want to
+ * keep that period small to reduce time lags).
+ */
+ step = 0;
+ if (dirty < setpoint) {
+ x = min(bdi->balanced_dirty_ratelimit,
+ min(balanced_dirty_ratelimit, task_ratelimit));
+ if (dirty_ratelimit < x)
+ step = x - dirty_ratelimit;
+ } else {
+ x = max(bdi->balanced_dirty_ratelimit,
+ max(balanced_dirty_ratelimit, task_ratelimit));
+ if (dirty_ratelimit > x)
+ step = dirty_ratelimit - x;
+ }
+
+ /*
+ * Don't pursue 100% rate matching. It's impossible since the balanced
+ * rate itself is constantly fluctuating. So decrease the track speed
+ * when it gets close to the target. Helps eliminate pointless tremors.
+ */
+ step >>= dirty_ratelimit / (2 * step + 1);
+ /*
+ * Limit the tracking speed to avoid overshooting.
+ */
+ step = (step + 7) / 8;
+
+ if (dirty_ratelimit < balanced_dirty_ratelimit)
+ dirty_ratelimit += step;
+ else
+ dirty_ratelimit -= step;
+
+ bdi->dirty_ratelimit = max(dirty_ratelimit, 1UL);
+ bdi->balanced_dirty_ratelimit = balanced_dirty_ratelimit;
+
+ trace_bdi_dirty_ratelimit(bdi, dirty_rate, task_ratelimit);
+}
+
void __bdi_update_bandwidth(struct backing_dev_info *bdi,
unsigned long thresh,
+ unsigned long bg_thresh,
unsigned long dirty,
unsigned long bdi_thresh,
unsigned long bdi_dirty,
{
unsigned long now = jiffies;
unsigned long elapsed = now - bdi->bw_time_stamp;
+ unsigned long dirtied;
unsigned long written;
/*
if (elapsed < BANDWIDTH_INTERVAL)
return;
+ dirtied = percpu_counter_read(&bdi->bdi_stat[BDI_DIRTIED]);
written = percpu_counter_read(&bdi->bdi_stat[BDI_WRITTEN]);
/*
if (elapsed > HZ && time_before(bdi->bw_time_stamp, start_time))
goto snapshot;
- if (thresh)
+ if (thresh) {
global_update_bandwidth(thresh, dirty, now);
-
+ bdi_update_dirty_ratelimit(bdi, thresh, bg_thresh, dirty,
+ bdi_thresh, bdi_dirty,
+ dirtied, elapsed);
+ }
bdi_update_write_bandwidth(bdi, elapsed, written);
snapshot:
+ bdi->dirtied_stamp = dirtied;
bdi->written_stamp = written;
bdi->bw_time_stamp = now;
}
static void bdi_update_bandwidth(struct backing_dev_info *bdi,
unsigned long thresh,
+ unsigned long bg_thresh,
unsigned long dirty,
unsigned long bdi_thresh,
unsigned long bdi_dirty,
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);
+ __bdi_update_bandwidth(bdi, thresh, bg_thresh, dirty,
+ bdi_thresh, bdi_dirty, start_time);
spin_unlock(&bdi->wb.list_lock);
}
+/*
+ * After a task dirtied this many pages, balance_dirty_pages_ratelimited_nr()
+ * will look to see if it needs to start dirty throttling.
+ *
+ * If dirty_poll_interval is too low, big NUMA machines will call the expensive
+ * global_page_state() too often. So scale it near-sqrt to the safety margin
+ * (the number of pages we may dirty without exceeding the dirty limits).
+ */
+static unsigned long dirty_poll_interval(unsigned long dirty,
+ unsigned long thresh)
+{
+ if (thresh > dirty)
+ return 1UL << (ilog2(thresh - dirty) >> 1);
+
+ return 1;
+}
+
+static unsigned 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;
+
+ /*
+ * Limit pause time for small memory systems. If sleeping for too long
+ * time, a small pool of dirty/writeback pages may go empty and disk go
+ * idle.
+ *
+ * 8 serves as the safety ratio.
+ */
+ if (bdi_dirty)
+ t = min(t, bdi_dirty * HZ / (8 * bw + 1));
+
+ /*
+ * 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.
+ */
+ return clamp_val(t, 4, MAX_PAUSE);
+}
+
/*
* 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;
+ long uninitialized_var(max_pause);
bool dirty_exceeded = false;
- bool clear_dirty_exceeded = true;
+ unsigned long task_ratelimit;
+ unsigned long uninitialized_var(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);
* catch-up. This avoids (excessively) small writeouts
* when the bdi limits are ramping up.
*/
- if (nr_dirty <= (background_thresh + dirty_thresh) / 2)
+ freerun = dirty_freerun_ceiling(dirty_thresh,
+ background_thresh);
+ 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
* 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, nr_dirty,
- bdi_thresh, bdi_dirty, start_time);
+ 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 */
+ 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);
+ 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);
+ if (unlikely(pause <= 0)) {
+ trace_balance_dirty_pages(bdi,
+ dirty_thresh,
+ background_thresh,
+ nr_dirty,
+ bdi_thresh,
+ bdi_dirty,
+ dirty_ratelimit,
+ task_ratelimit,
+ pages_dirtied,
+ pause,
+ start_time);
+ pause = 1; /* avoid resetting nr_dirtied_pause below */
+ break;
}
+ pause = min(pause, max_pause);
+
+pause:
+ trace_balance_dirty_pages(bdi,
+ dirty_thresh,
+ background_thresh,
+ nr_dirty,
+ bdi_thresh,
+ bdi_dirty,
+ dirty_ratelimit,
+ task_ratelimit,
+ pages_dirtied,
+ pause,
+ start_time);
__set_current_state(TASK_UNINTERRUPTIBLE);
io_schedule_timeout(pause);
- trace_balance_dirty_wait(bdi);
dirty_thresh = hard_dirty_limit(dirty_thresh);
/*
* 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;
+ 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;
* 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);
}
}
}
-static DEFINE_PER_CPU(unsigned long, bdp_ratelimits) = 0;
+static DEFINE_PER_CPU(int, bdp_ratelimits);
/**
* balance_dirty_pages_ratelimited_nr - balance dirty memory state
unsigned long nr_pages_dirtied)
{
struct backing_dev_info *bdi = mapping->backing_dev_info;
- unsigned long ratelimit;
- unsigned long *p;
+ int ratelimit;
+ int *p;
if (!bdi_cap_account_dirty(bdi))
return;
- ratelimit = ratelimit_pages;
- if (mapping->backing_dev_info->dirty_exceeded)
- ratelimit = 8;
+ ratelimit = current->nr_dirtied_pause;
+ if (bdi->dirty_exceeded)
+ ratelimit = min(ratelimit, 32 >> (PAGE_SHIFT - 10));
+
+ current->nr_dirtied += nr_pages_dirtied;
+ preempt_disable();
/*
- * Check the rate limiting. Also, we do not want to throttle real-time
- * tasks in balance_dirty_pages(). Period.
+ * This prevents one CPU to accumulate too many dirtied pages without
+ * calling into balance_dirty_pages(), which can happen when there are
+ * 1000+ tasks, all of them start dirtying pages at exactly the same
+ * time, hence all honoured too large initial task->nr_dirtied_pause.
*/
- preempt_disable();
p = &__get_cpu_var(bdp_ratelimits);
- *p += nr_pages_dirtied;
- if (unlikely(*p >= ratelimit)) {
- ratelimit = sync_writeback_pages(*p);
+ if (unlikely(current->nr_dirtied >= ratelimit))
*p = 0;
- preempt_enable();
- balance_dirty_pages(mapping, ratelimit);
- return;
+ else {
+ *p += nr_pages_dirtied;
+ if (unlikely(*p >= ratelimit_pages)) {
+ *p = 0;
+ ratelimit = 0;
+ }
}
preempt_enable();
+
+ if (unlikely(current->nr_dirtied >= ratelimit))
+ balance_dirty_pages(mapping, current->nr_dirtied);
}
EXPORT_SYMBOL(balance_dirty_pages_ratelimited_nr);
* threshold
*/
if (bdi_has_dirty_io(&q->backing_dev_info))
- bdi_start_writeback(&q->backing_dev_info, nr_pages);
+ bdi_start_writeback(&q->backing_dev_info, nr_pages,
+ WB_REASON_LAPTOP_TIMER);
}
/*
*
* Here we set ratelimit_pages to a level which ensures that when all CPUs are
* dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
- * thresholds before writeback cuts in.
- *
- * But the limit should not be set too high. Because it also controls the
- * amount of memory which the balance_dirty_pages() caller has to write back.
- * If this is too large then the caller will block on the IO queue all the
- * time. So limit it to four megabytes - the balance_dirty_pages() caller
- * will write six megabyte chunks, max.
+ * thresholds.
*/
void writeback_set_ratelimit(void)
{
- ratelimit_pages = vm_total_pages / (num_online_cpus() * 32);
+ unsigned long background_thresh;
+ unsigned long dirty_thresh;
+ global_dirty_limits(&background_thresh, &dirty_thresh);
+ ratelimit_pages = dirty_thresh / (num_online_cpus() * 32);
if (ratelimit_pages < 16)
ratelimit_pages = 16;
- if (ratelimit_pages * PAGE_CACHE_SIZE > 4096 * 1024)
- ratelimit_pages = (4096 * 1024) / PAGE_CACHE_SIZE;
}
static int __cpuinit
__inc_zone_page_state(page, NR_FILE_DIRTY);
__inc_zone_page_state(page, NR_DIRTIED);
__inc_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE);
+ __inc_bdi_stat(mapping->backing_dev_info, BDI_DIRTIED);
task_dirty_inc(current);
task_io_account_write(PAGE_CACHE_SIZE);
}
git.openpandora.org / pandora-kernel.git / commitdiff