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 -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html