On Tue, 2 Jan 2001, Linus Torvalds wrote:
> On Tue, 2 Jan 2001, Mike Galbraith wrote:
> >
> > Yes and no. I've seen nasty stalls for quite a while now. (I think
> > that there is a wakeup problem lurking)
> >
> > I found the change which triggers my horrid stalls. Nobody is going
> > to believe this...
>
> Hmm.. I can believe it. The code that waits on bdflush in wakeup_bdflush()
> is somewhat suspicious. In particular, if/when that ever triggers, and
> bdflush() is busy in flush_dirty_buffers(), then the process that is
> trying to wake bdflush up is going to wait until flush_dirty_buffers() is
> done.
>
> Which, if there is a process dirtying pages, can basically be
> pretty much forever.
>
> This was probably hidden by the lower limits simply by virtue of bdflush
> never being very active before.
>
> What does the system feel like if you just change the "sleep for bdflush"
> logic in wakeup_bdflush() to something like
>
> wake_up_process(bdflush_tsk);
> __set_current_state(TASK_RUNNING);
> current->policy |= SCHED_YIELD;
> schedule();
>
> instead of trying to wait for bdflush to wake us up?
No difference (except more context switching as expected)
-Mike
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