Re: [RFC][PATCH -mm 7/7] Freezer: Use freezing timeout more efficiently

[Pavel Machek <pavel@ucw.cz>]

Hi!

> There is the problem with try_to_freeze_tasks() that it always loops until the
> timeout expires, even if it is certain to fail much earlier.  Namely, if there
> are uninterruptible tasks waiting for some frozen tasks to let them continue,
> try_to_freeze_tasks() will certainly fail and it shouldn't waste time in that
> cases.
> 
> To detect such situations, we can check if the number of tasks that haven't
> frozen yet changes between subsequent iterations of the main loop in
> try_to_freeze_tasks().  If this number hasn't been changing for sufficiently
> long time (say, 250 ms), then most probably some uninterruptible tasks are
> blocked by some frozen tasks and we should break out of this stalemate.  Thus,
> it seems reasonable to thaw the tasks that have already been frozen without
> clearing the freeze requests of the tasks that are refusing to freeze.  This
> way, if these tasks are really blocked by the frozen ones, they will get extra
> chance to freeze themselves after we have thawed the other tasks and before we
> request those tasks to freeze again.  Next, the freezing loop can be repeated
> and so on, until all tasks are frozen or the timeout expires.

I still don't quite like this patch... it is kind of trick we should
not have to play. Can we at least get confirmation it helps in the
FUSE case?
								Pavel

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