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    SubjectRe: [PATCH 05/17] writeback: quit throttling when signal pending
    On Mon, Sep 13, 2010 at 11:21:16AM +0800, Neil Brown wrote:
    > On Mon, 13 Sep 2010 09:55:29 +0800
    > Wu Fengguang <fengguang.wu@intel.com> wrote:
    >
    > > On Mon, Sep 13, 2010 at 04:46:54AM +0800, Neil Brown wrote:
    > > > On Sun, 12 Sep 2010 23:49:50 +0800
    > > > Wu Fengguang <fengguang.wu@intel.com> wrote:
    > > >
    > > > > This allows quick response to Ctrl-C etc. for impatient users.
    > > > >
    > > > > Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
    > > > > ---
    > > > > mm/page-writeback.c | 3 +++
    > > > > 1 file changed, 3 insertions(+)
    > > > >
    > > > > --- linux-next.orig/mm/page-writeback.c 2010-09-09 16:01:14.000000000 +0800
    > > > > +++ linux-next/mm/page-writeback.c 2010-09-09 16:02:27.000000000 +0800
    > > > > @@ -553,6 +553,9 @@ static void balance_dirty_pages(struct a
    > > > > __set_current_state(TASK_INTERRUPTIBLE);
    > > > > io_schedule_timeout(pause);
    > > > >
    > > > > + if (signal_pending(current))
    > > > > + break;
    > > > > +
    > > >
    > > > Given the patch description, I think you might want "fatal_signal_pending()"
    > > > here ???
    > >
    > > __fatal_signal_pending() tests SIGKILL only, while the one often used
    > > and need more quick responding is SIGINT..
    > >
    >
    > I thought that at first too.... but I don't think that is the case.
    >
    > In kernel/signal.c, in complete_signal, we have
    > if (sig_fatal() ...)
    > ....
    > sigaddset(&t->pending.signal, SIGKILL);
    >
    > where sig_fatal is
    >
    > #define sig_fatal(t, signr) \
    > (!siginmask(signr, SIG_KERNEL_IGNORE_MASK|SIG_KERNEL_STOP_MASK) && \
    > (t)->sighand->action[(signr)-1].sa.sa_handler == SIG_DFL)
    >
    >
    > so (if I'm reading the code correctly), if a process receives a signal for
    > which the handler is SIG_DFL, then SIGKILL is set in the pending mask, so
    > __fatal_signal_pending will be true.
    >
    > So it fatal_signal_pending should catch any signal that will cause the
    > process to exit. I assume that it what you want...

    Ah yes, it does look so. Thanks for the detailed explanation!
    Here is the updated patch.

    Thanks,
    Fengguang
    ---
    Subject: writeback: quit throttling when fatal signal pending
    From: Wu Fengguang <fengguang.wu@intel.com>
    Date: Wed Sep 08 17:40:22 CST 2010

    This allows quick response to Ctrl-C etc. for impatient users.

    It mainly helps the rare bdi/global dirty exceeded cases.
    In the normal case of not exceeded, it will quit the loop anyway.

    CC: Neil Brown <neilb@suse.de>
    Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
    ---
    mm/page-writeback.c | 3 +++
    1 file changed, 3 insertions(+)

    --- linux-next.orig/mm/page-writeback.c 2010-09-12 13:25:23.000000000 +0800
    +++ linux-next/mm/page-writeback.c 2010-09-13 11:39:33.000000000 +0800
    @@ -552,6 +552,9 @@ static void balance_dirty_pages(struct a
    __set_current_state(TASK_INTERRUPTIBLE);
    io_schedule_timeout(pause);

    + if (fatal_signal_pending(current))
    + break;
    +
    check_exceeded:
    /*
    * The bdi thresh is somehow "soft" limit derived from the

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