Hi,
On Wed, Mar 09, 2016 at 05:52:01PM -0800, Hong Mei Li wrote:
> Thank you Jaegeuk for your quick response.
>
> When using io_schedule_timeout(timeout), seems the timeout parameter is not
> easy to be determined.
>
> We do not know how many data to be transferred.
>
> If we have large amount of data to transact, and the timeout parameter is
> small,
> the waiting task would be waken up several times redundantly and then just
> back to sleep again.
Currently 5*HZ is used.
I think it's okay since wait_on_all_pages_writeback is called only by
checkpoint, which means every operations are waiting for this ends up.
Moreover scheduling redundantly would not a big deal, and pretty rare even.
If we can rely on timeout, we can avoid smp_mb overhead in every end_io too.
Thanks,
>
> Otherwise, if the timeout parameter is big, then, we are just replacing the
> always stuck problem with a long time stuck?
>
> By comparing the implementation of wq_has_sleeper and sock_poll_wait,
> we do need paired smp_mb in both wait_on_all_pages_writeback and end_io.
>
> Thanks
> Hongmei
>
>
>
> On Wed, Mar 9, 2016 at 5:03 PM, Jaegeuk Kim <jaeg...@kernel.org> wrote:
>
> > Hi Hong Mei,
> >
> > In order to avoid this problem, we already added wq_has_sleeper() which
> > calls
> > smp_mb() in end_io, and use io_schedule_timeout() instead of io_schedule()
> > in
> > wait_on_all_pages_writeback().
> >
> > How do you think whether this is enough or not?
> >
> > Thanks,
> >
> > On Wed, Mar 09, 2016 at 01:42:12PM -0800, Hong Mei Li wrote:
> > > From: Hong-Mei Li <a21...@motorola.com>
> > >
> > >
> > > Sometimes, f2fs fdatasync would stuck at wait_on_all_pages_writeback
> > > with pages count == 0 and itself in the waitlist.
> > >
> > > Fix it by adding an explicit smp_mb() after writting wait list, to make
> > > sure the store is done before get_pages.
> > > And add another memory barrier in wakeup side, to make sure cpu reading
> > > wait list happens after decreased pages count syncing to memory.
> > >
> > > Signed-off-by: Hong-Mei Li <a21...@motorola.com>
> > > Cc: linux-f2fs-devel@lists.sourceforge.net
> > > Cc: Jaegeuk Kim <jaeg...@kernel.org>
> > >
> > > ---
> > > fs/f2fs/checkpoint.c | 1 +
> > > fs/f2fs/data.c | 1 +
> > > 2 files changed, 2 insertions(+)
> > >
> > > diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
> > > index 3842af9..4e5acab 100644
> > > --- a/fs/f2fs/checkpoint.c
> > > +++ b/fs/f2fs/checkpoint.c
> > > @@ -899,6 +899,7 @@ static void wait_on_all_pages_writeback(struct
> > > f2fs_sb_info *sbi)
> > > for (;;) {
> > > prepare_to_wait(&sbi->cp_wait, &wait,
> > TASK_UNINTERRUPTIBLE);
> > >
> > > + smp_mb();
> > > if (!get_pages(sbi, F2FS_WRITEBACK))
> > > break;
> > >
> > > diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> > > index 5c06db1..b1d383c 100644
> > > --- a/fs/f2fs/data.c
> > > +++ b/fs/f2fs/data.c
> > > @@ -75,6 +75,7 @@ static void f2fs_write_end_io(struct bio *bio)
> > > dec_page_count(sbi, F2FS_WRITEBACK);
> > > }
> > >
> > > + smp_mb();
> > > if (!get_pages(sbi, F2FS_WRITEBACK) &&
> > > !list_empty(&sbi->cp_wait.task_list))
> > > wake_up(&sbi->cp_wait);
> > > --
> > > 1.9.1
> >
>
>
>
> --
>
> Thanks and Regards
> Hongmei
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