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SubjectRe: spindown [was Re: 2.4.6-pre2, pre3 VM Behavior]
On Sat, 16 Jun 2001, Daniel Phillips wrote:

> On Saturday 16 June 2001 23:06, Rik van Riel wrote:
> > On Sat, 16 Jun 2001, Daniel Phillips wrote:
> > > As a side note, the good old multisecond delay before bdflush kicks in
> > > doesn't really make a lot of sense - when bandwidth is available the
> > > filesystem-initiated writeouts should happen right away.
> >
> > ... thus spinning up the disk ?
>
> Nope, the disk is already spinning, some other writeouts just finished.
>
> > How about just making sure we write out a bigger bunch
> > of dirty pages whenever one buffer gets too old ?
>
> It's simpler than that. It's basically just: disk traffic low? good, write
> out all the dirty buffers. Not quite as crude as that, but nearly.
>
> > Does the patch below do anything good for your laptop? ;)
>
> I'll wait for the next one ;-)

Greetings! (well, not next one, but one anyway)

It _juuust_ so happens that I was tinkering... what do you think of
something like the below? (and boy do I ever wonder what a certain
box doing slrn stuff thinks of it.. hint hint;)

-Mike

Doing Bonnie in big fragmented 1k bs partition on the worst spot on
the disk. Bad benchmark, bad conditions.. but interesting results.

2.4.6.pre3 before
-------Sequential Output-------- ---Sequential Input-- --Random--
-Per Char- --Block--- -Rewrite-- -Per Char- --Block--- --Seeks---
MB K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU /sec %CPU
500 9609 36.0 10569 14.3 3322 6.4 9509 47.6 10597 13.8 101.7 1.4

2.4.6.pre3 after (using flushto behavior as in defaults)
-------Sequential Output-------- ---Sequential Input-- --Random--
-Per Char- --Block--- -Rewrite-- -Per Char- --Block--- --Seeks---
MB K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU /sec %CPU
500 8293 30.2 11834 29.4 5072 9.5 8879 44.1 10597 13.6 100.4 0.9


2.4.6.pre3 after (flushto = ndirty)
-------Sequential Output-------- ---Sequential Input-- --Random--
-Per Char- --Block--- -Rewrite-- -Per Char- --Block--- --Seeks---
MB K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU /sec %CPU
500 10286 38.4 10715 14.4 3267 6.1 9605 47.6 10596 13.4 102.7 1.6


--- fs/buffer.c.org Fri Jun 15 06:48:17 2001
+++ fs/buffer.c Sun Jun 17 09:14:17 2001
@@ -118,20 +118,21 @@
wake-cycle */
int nrefill; /* Number of clean buffers to try to obtain
each time we call refill */
- int dummy1; /* unused */
+ int nflushto; /* Level to flush down to once bdflush starts */
int interval; /* jiffies delay between kupdate flushes */
int age_buffer; /* Time for normal buffer to age before we flush it */
int nfract_sync; /* Percentage of buffer cache dirty to
activate bdflush synchronously */
- int dummy2; /* unused */
+ int nmonitor; /* Size (%physpages) at which bdflush should
+ begin monitoring the buffercache */
int dummy3; /* unused */
} b_un;
unsigned int data[N_PARAM];
-} bdf_prm = {{30, 64, 64, 256, 5*HZ, 30*HZ, 60, 0, 0}};
+} bdf_prm = {{60, 64, 64, 50, 5*HZ, 30*HZ, 85, 15, 0}};

/* These are the min and max parameter values that we will allow to be assigned */
-int bdflush_min[N_PARAM] = { 0, 10, 5, 25, 0, 1*HZ, 0, 0, 0};
-int bdflush_max[N_PARAM] = {100,50000, 20000, 20000,600*HZ, 6000*HZ, 100, 0, 0};
+int bdflush_min[N_PARAM] = {0, 10, 5, 0, 0, 1*HZ, 0, 0, 0};
+int bdflush_max[N_PARAM] = {100,50000, 20000, 100,600*HZ, 6000*HZ, 100, 100, 0};

/*
* Rewrote the wait-routines to use the "new" wait-queue functionality,
@@ -763,12 +764,8 @@
balance_dirty(NODEV);
if (free_shortage())
page_launder(GFP_BUFFER, 0);
- if (!grow_buffers(size)) {
+ if (!grow_buffers(size))
wakeup_bdflush(1);
- current->policy |= SCHED_YIELD;
- __set_current_state(TASK_RUNNING);
- schedule();
- }
}

void init_buffer(struct buffer_head *bh, bh_end_io_t *handler, void *private)
@@ -1042,25 +1039,43 @@
1 -> sync flush (wait for I/O completion) */
int balance_dirty_state(kdev_t dev)
{
- unsigned long dirty, tot, hard_dirty_limit, soft_dirty_limit;
-
- dirty = size_buffers_type[BUF_DIRTY] >> PAGE_SHIFT;
- tot = nr_free_buffer_pages();
+ unsigned long dirty, cache, buffers = 0;
+ int i;

- dirty *= 100;
- soft_dirty_limit = tot * bdf_prm.b_un.nfract;
- hard_dirty_limit = tot * bdf_prm.b_un.nfract_sync;
-
- /* First, check for the "real" dirty limit. */
- if (dirty > soft_dirty_limit) {
- if (dirty > hard_dirty_limit)
+ for (i = 0; i < NR_LIST; i++)
+ buffers += size_buffers_type[i];
+ buffers >>= PAGE_SHIFT;
+ if (buffers * 100 < num_physpages * bdf_prm.b_un.nmonitor)
+ return -1;
+
+ buffers *= bdf_prm.b_un.nfract;
+ dirty = 100 * (size_buffers_type[BUF_DIRTY] >> PAGE_SHIFT);
+ cache = atomic_read(&page_cache_size) + nr_free_pages();
+ cache *= bdf_prm.b_un.nfract_sync;
+ if (dirty > buffers) {
+ if (dirty > cache)
return 1;
return 0;
}
-
return -1;
}

+int balance_dirty_done(kdev_t dev)
+{
+ unsigned long dirty, buffers = 0;
+ int i;
+
+ for (i = 0; i < NR_LIST; i++)
+ buffers += size_buffers_type[i];
+ buffers >>= PAGE_SHIFT;
+ buffers *= bdf_prm.b_un.nflushto;
+ dirty = 100 * (size_buffers_type[BUF_DIRTY] >> PAGE_SHIFT);
+
+ if (dirty < buffers)
+ return 1;
+ return 0;
+}
+
/*
* if a new dirty buffer is created we need to balance bdflush.
*
@@ -2528,9 +2543,15 @@
static int flush_dirty_buffers(int check_flushtime)
{
struct buffer_head * bh, *next;
- int flushed = 0, i;
+ int flushed = 0, weight = 0, i;

restart:
+ /*
+ * If we have a shortage, we have been laundering and reclaiming
+ * or will be. In either case, we should adjust flush weight.
+ */
+ if (!check_flushtime && current->mm)
+ weight += (free_shortage() + inactive_shortage()) >> 4;
spin_lock(&lru_list_lock);
bh = lru_list[BUF_DIRTY];
if (!bh)
@@ -2552,9 +2573,6 @@
will be too young. */
if (time_before(jiffies, bh->b_flushtime))
goto out_unlock;
- } else {
- if (++flushed > bdf_prm.b_un.ndirty)
- goto out_unlock;
}

/* OK, now we are committed to write it out. */
@@ -2563,8 +2581,14 @@
ll_rw_block(WRITE, 1, &bh);
atomic_dec(&bh->b_count);

- if (current->need_resched)
+ if (++flushed >= bdf_prm.b_un.ndirty + weight ||
+ current->need_resched) {
+ /* kflushd and user tasks return to schedule points. */
+ if (!check_flushtime)
+ return flushed;
+ flushed = 0;
schedule();
+ }
goto restart;
}
out_unlock:
@@ -2580,8 +2604,14 @@
if (waitqueue_active(&bdflush_wait))
wake_up_interruptible(&bdflush_wait);

- if (block)
+ if (block) {
flush_dirty_buffers(0);
+ if (current->mm) {
+ current->policy |= SCHED_YIELD;
+ __set_current_state(TASK_RUNNING);
+ schedule();
+ }
+ }
}

/*
@@ -2672,7 +2702,7 @@
int bdflush(void *sem)
{
struct task_struct *tsk = current;
- int flushed;
+ int flushed, state;
/*
* We have a bare-bones task_struct, and really should fill
* in a few more things so "top" and /proc/2/{exe,root,cwd}
@@ -2696,13 +2726,17 @@
CHECK_EMERGENCY_SYNC

flushed = flush_dirty_buffers(0);
+ state = balance_dirty_state(NODEV);
+ if (state == 1)
+ run_task_queue(&tq_disk);

/*
- * If there are still a lot of dirty buffers around,
- * skip the sleep and flush some more. Otherwise, we
- * go to sleep waiting a wakeup.
+ * If there are still a lot of dirty buffers around, schedule
+ * and flush some more. Otherwise, go back to sleep.
*/
- if (!flushed || balance_dirty_state(NODEV) < 0) {
+ if (current->need_resched || state == 0)
+ schedule();
+ else if (!flushed || balance_dirty_done(NODEV)) {
run_task_queue(&tq_disk);
interruptible_sleep_on(&bdflush_wait);
}
@@ -2738,7 +2772,11 @@
interval = bdf_prm.b_un.interval;
if (interval) {
tsk->state = TASK_INTERRUPTIBLE;
+sleep:
schedule_timeout(interval);
+ /* Get out of the way if kflushd is running. */
+ if (!waitqueue_active(&bdflush_wait))
+ goto sleep;
} else {
stop_kupdate:
tsk->state = TASK_STOPPED;
-
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