linux-toradex.git/lib/percpu_counter.c, branch v2.6.28

revert "percpu_counter: new function percpu_counter_sum_and_set"

2008-12-10T16:01:52+00:00

Revert

    commit e8ced39d5e8911c662d4d69a342b9d053eaaac4e
    Author: Mingming Cao 
    Date:   Fri Jul 11 19:27:31 2008 -0400

        percpu_counter: new function percpu_counter_sum_and_set

As described in

	revert "percpu counter: clean up percpu_counter_sum_and_set()"

the new percpu_counter_sum_and_set() is racy against updates to the
cpu-local accumulators on other CPUs.  Revert that change.

This means that ext4 will be slow again.  But correct.

Reported-by: Eric Dumazet 
Cc: "David S. Miller" 
Cc: Peter Zijlstra 
Cc: Mingming Cao 
Cc: 
Cc: 		[2.6.27.x]
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

revert "percpu counter: clean up percpu_counter_sum_and_set()"

2008-12-10T16:01:52+00:00

Revert

    commit 1f7c14c62ce63805f9574664a6c6de3633d4a354
    Author: Mingming Cao 
    Date:   Thu Oct 9 12:50:59 2008 -0400

        percpu counter: clean up percpu_counter_sum_and_set()

Before this patch we had the following:

percpu_counter_sum(): return the percpu_counter's value

percpu_counter_sum_and_set(): return the percpu_counter's value, copying
that value into the central value and zeroing the per-cpu counters before
returning.

After this patch, percpu_counter_sum_and_set() has gone, and
percpu_counter_sum() gets the old percpu_counter_sum_and_set()
functionality.

Problem is, as Eric points out, the old percpu_counter_sum_and_set()
functionality was racy and wrong.  It zeroes out counters on "other" cpus,
without holding any locks which will prevent races agaist updates from
those other CPUS.

This patch reverts 1f7c14c62ce63805f9574664a6c6de3633d4a354.  This means
that percpu_counter_sum_and_set() still has the race, but
percpu_counter_sum() does not.

Note that this is not a simple revert - ext4 has since started using
percpu_counter_sum() for its dirty_blocks counter as well.

Note that this revert patch changes percpu_counter_sum() semantics.

Before the patch, a call to percpu_counter_sum() will bring the counter's
central counter mostly up-to-date, so a following percpu_counter_read()
will return a close value.

After this patch, a call to percpu_counter_sum() will leave the counter's
central accumulator unaltered, so a subsequent call to
percpu_counter_read() can now return a significantly inaccurate result.

If there is any code in the tree which was introduced after
e8ced39d5e8911c662d4d69a342b9d053eaaac4e was merged, and which depends
upon the new percpu_counter_sum() semantics, that code will break.

Reported-by: Eric Dumazet 
Cc: "David S. Miller" 
Cc: Peter Zijlstra 
Cc: Mingming Cao 
Cc: 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

percpu_counter: fix CPU unplug race in percpu_counter_destroy()

2008-12-10T16:01:52+00:00

We should first delete the counter from percpu_counters list
before freeing memory, or a percpu_counter_hotcpu_callback()
could dereference a NULL pointer.

Signed-off-by: Eric Dumazet 
Acked-by: David S. Miller 
Cc: Peter Zijlstra 
Cc: Mingming Cao 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

percpu counter: clean up percpu_counter_sum_and_set()

2008-10-09T16:50:59+00:00

percpu_counter_sum_and_set() and percpu_counter_sum() is the same except
the former updates the global counter after accounting.  Since we are
taking the fbc->lock to calculate the precise value of the counter in
percpu_counter_sum() anyway, it should simply set fbc->count too, as the
percpu_counter_sum_and_set() does.

This patch merges these two interfaces into one.
 
Signed-off-by: Mingming Cao 
Acked-by: Peter Zijlstra 
Cc: 
Signed-off-by: Andrew Morton 
Signed-off-by: "Theodore Ts'o"

percpu_counter: new function percpu_counter_sum_and_set

2008-07-11T23:27:31+00:00

Delayed allocation need to check free blocks at every write time.
percpu_counter_read_positive() is not quit accurate. delayed
allocation need a more accurate accounting, but using
percpu_counter_sum_positive() is frequently is quite expensive.

This patch added a new function to update center counter when sum
per-cpu counter, to increase the accurate rate for next
percpu_counter_read() and require less calling expensive
percpu_counter_sum().

Signed-off-by: Mingming Cao 
Signed-off-by: "Theodore Ts'o"

mm: bdi: export BDI attributes in sysfs

2008-04-30T15:29:49+00:00

Provide a place in sysfs (/sys/class/bdi) for the backing_dev_info object.
This allows us to see and set the various BDI specific variables.

In particular this properly exposes the read-ahead window for all relevant
users and /sys/block//queue/read_ahead_kb should be deprecated.

With patient help from Kay Sievers and Greg KH

[mszeredi@suse.cz]

 - split off NFS and FUSE changes into separate patches
 - document new sysfs attributes under Documentation/ABI
 - do bdi_class_init as a core_initcall, otherwise the "default" BDI
   won't be initialized
 - remove bdi_init_fmt macro, it's not used very much

[akpm@linux-foundation.org: fix ia64 warning]
Signed-off-by: Peter Zijlstra 
Cc: Kay Sievers 
Acked-by: Greg KH 
Cc: Trond Myklebust 
Signed-off-by: Miklos Szeredi 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

Add irq protection in the percpu-counters cpu-hotplug-callback path

2007-10-19T18:53:44+00:00

Some of the per-cpu counters and thus their locks are accessed from IRQ
contexts.  This can cause a deadlock if it interrupts a cpu-offline thread
which is transferring a dead-cpu's counts to the global counter.

Add appropriate IRQ protection in the cpu-hotplug callback path.

Signed-off-by: Gautham R Shenoy 
Cc: KAMEZAWA Hiroyuki 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

lib: percpu_counter_init_irq

2007-10-17T15:42:44+00:00

provide a way to tell lockdep about percpu_counters that are supposed to be
used from irq safe contexts.

Signed-off-by: Peter Zijlstra 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

lib: percpu_counter_init error handling

2007-10-17T15:42:44+00:00

alloc_percpu can fail, propagate that error.

Signed-off-by: Peter Zijlstra 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

lib: percpu_count_sum()

2007-10-17T15:42:44+00:00

Provide an accurate version of percpu_counter_read.

Signed-off-by: Peter Zijlstra 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds