lkml.org 
[lkml]   [2010]   [May]   [12]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH -mm] cpuset,mm: fix no node to alloc memory when changing cpuset's mems - fix2
On Wed, 12 May 2010 17:00:45 +0800
Miao Xie <miaox@cn.fujitsu.com> wrote:

> on 2010-5-12 12:32, Andrew Morton wrote:
> > On Wed, 12 May 2010 15:20:51 +0800 Miao Xie <miaox@cn.fujitsu.com> wrote:
> >
> >> @@ -985,6 +984,7 @@ repeat:
> >> * for the read-side.
> >> */
> >> while (ACCESS_ONCE(tsk->mems_allowed_change_disable)) {
> >> + task_unlock(tsk);
> >> if (!task_curr(tsk))
> >> yield();
> >> goto repeat;
> >
> > Oh, I meant to mention that. No yield()s, please. Their duration is
> > highly unpredictable. Can we do something more deterministic here?
>
> Maybe we can use wait_for_completion().

That would work.

> >
> > Did you consider doing all this with locking? get_mems_allowed() does
> > mutex_lock(current->lock)?
>
> do you means using a real lock(such as: mutex) to protect mempolicy and mem_allowed?

yes.

> It may cause the performance regression, so I do my best to abstain from using a real
> lock.

Well, the code as-is is pretty exotic with lots of open-coded tricky
barriers - it's best to avoid inventing new primitives if possible.
For example, there's no lockdep support for this new "lock".

mutex_lock() is pretty quick - basically a simgle atomic op. How
frequently do these operations occur?

The code you have at present is fairly similar to sequence locks. I
wonder if there's some way of (ab)using sequence locks for this.
seqlocks don't have lockdep support either...



\
 
 \ /
  Last update: 2010-05-12 19:51    [W:0.052 / U:3.428 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site