On Mon, Jun 21, 2010 at 03:42:39PM +0200, Jan Kara wrote:
> On Fri 18-06-10 12:21:37, Peter Zijlstra wrote:
> > On Thu, 2010-06-17 at 20:04 +0200, Jan Kara wrote:
> > > + if (bdi_stat(bdi, BDI_WRITTEN) >= bdi->wb_written_head)
> > > + bdi_wakeup_writers(bdi);
> >
> > For the paranoid amongst us you could make wb_written_head s64 and write
> > the above as:
> >
> > if (bdi_stat(bdi, BDI_WRITTEN) - bdi->wb_written_head > 0)
> >
> > Which, if you assume both are monotonic and wb_written_head is always
> > within 2^63 of the actual bdi_stat() value, should give the same end
> > result and deal with wrap-around.
> >
> > For when we manage to create a device that can write 2^64 pages in our
> > uptime :-)
> OK, the fix is simple enough so I've changed it, although I'm not
> paranoic enough ;) (I actually did the math before writing that test).
a bit more change :)
type:
- u64 wb_written_head
+ s64 wb_written_head
resetting:
- bdi->wb_written_head = ~(u64)0;
+ bdi->wb_written_head = 0;
setting:
bdi->wb_written_head = bdi_stat(bdi, BDI_WRITTEN) + wc->written;
+ bdi->wb_written_head |= 1;
testing:
if (bdi->wb_written_head &&
bdi_stat(bdi, BDI_WRITTEN) - bdi->wb_written_head > 0)
This avoids calling into bdi_wakeup_writers() pointlessly when no one
is being throttled (which is the normal case).
Thanks,
Fengguang
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