On Monday, 23 April 2007 16:19, Gautham R Shenoy wrote: > Hi Satyam, > On Mon, Apr 23, 2007 at 09:39:30AM +0530, Satyam Sharma wrote: > > Hi Rafael, > > > > >+/* > > >+ * Per task flags used by the freezer > > >+ * > > >+ * They should not be referred to directly outside of this file. > > >+ */ > > >+#define TFF_NOFREEZE 0 /* task should not be frozen */ > > >+#define TFF_FREEZE 8 /* task should go to the refrigerator ASAP > > >*/ > > >+#define TFF_SKIP 9 /* do not count this task as freezable */ > > >+#define TFF_FROZEN 10 /* task is frozen */ > > > > Aren't NOFREEZE and SKIP doing the same thing? One of them appears > > superfluous. I'm looking at 21-rc6-mm1 and vfork(2) seems to be its > > only user. Seeing how vfork(2) used it, can't the call to > > freezer_do_not_count() be replaced with a call to freezer_exempt()? > > Similarly, the freezer_count() after the wait_for_completion might > > just as well be a clear of the NOFREEZE bit followed by a > > try_to_freeze(). Could you please explain the rationale behind the > > SKIP flag? > > The difference between the NOFREEZE and the SKIP flag is a subtle one. > > When a task (say p) sets it's NOFREEZE flag, it tells the freezer not to > consider it for freezing. Which means freezeable(p) will return 0. > So the freezer will not even mark it for freezing. > > However, when a task sets it SKIP flag, it tells the freezer - "I might > block at a safe place. So when you are counting the processes which > have been marked as freezeable, but have not frozen yet, please don't > count me in. IOW, please skip me." > Thus such a task can still be marked for freezing. > > The typical usage is > freezer_do_not_count(current); > /* currents goes to an uninterruptible sleep, like wait_for_completion. */ > freezer_count(current); > > Once the task wakes up from it's uninterruptible sleep, it will > call freezer_count which in turn calls try_to_freeze. > If the task was marked for freezing, it will be frozen now. > > You may want to check the thread http://lkml.org/lkml/2007/2/18/47 > on how it came into existance.
Very well explained. Thanks! Greetings, Rafael - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
