Nick Piggin <piggin@cyberone.com.au> wrote:
>
> it seems to me that
> doing writeout whenever the disk would otherwise be idle
> (and we have dirty memory to write out) would be a good
> solution.
This is what the recently-removed BDI_read_active flag in backing_dev_info
was supposed to be for. I let it go because I don't think it's terribly
important and it's time to stop fiddling with the vfs writeout code and it
wasn't right anyway.
Note that 2.5 starts pdflush writeout at 10% of memory dirty. Or even lower
if there is a lot of mapped memory around. Whereas 2.4 will start background
writeout at 30% or 40% dirty. That's a fairly significant tuning change.
The algorithm for utilisation of an idle disk should be, in
balance_dirty_pages():
if (ps.nr_dirty + ps.nr_writeback < background_thresh) {
if (time_after(jiffies, bdi->last_read + HZ/100)) {
if (bdi->write_requests_in_flight < 2) {
struct writeback_control wbc = {
.bdi = bdi,
.sync_mode = WB_SYNC_NONE,
.nr_to_write = write_chunk,
};
writeback_inodes(&wbc);
}
}
return;
}
Or something like that. It's pretty close.
It could have pretty bad failure modes. Short-lived files in /tmp now
perform writeout, which needs to be waited on when those files are removed.
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This archive was generated by hypermail 2b29 : Mon Mar 31 2003 - 22:00:37 EST