On Thu, 2007-04-05 at 15:44 -0700, Andrew Morton wrote: > On Thu, 05 Apr 2007 19:42:18 +0200 > [EMAIL PROTECTED] wrote: > > > rely on accurate dirty page accounting to provide enough push back > > I think we'd like to see a bit more justification than that, please.
it should read like this: for ( ; ; ) { get_dirty_limits(&background_thresh, &dirty_thresh, NULL, NULL); /* * Boost the allowable dirty threshold a bit for page * allocators so they don't get DoS'ed by heavy writers */ dirty_thresh += dirty_thresh / 10; /* wheeee... */ if (global_page_state(NR_FILE_DIRTY) + global_page_state(NR_UNSTABLE_NFS) + global_page_state(NR_WRITEBACK) <= dirty_thresh) break; congestion_wait(WRITE, HZ/10); } [ note the extra NR_FILE_DIRTY ] now, balance_dirty_pages() is there to ensure: nr_dirty + nr_unstable + nr_writeback < dirty_thresh (1) reclaim will (with the introduction of dirty page tracking) never generate dirty pages, so the only disturbance of that equation is an increase in nr_writeback. [ pageout() sets wbc.for_reclaim=1, so NFS traffic will not generate unstable pages ] So, what throttle_vm_writeout() does is limit the number of added writeback pages to 10% of the total limit. pageout() seems to avoid stuffing pages down a congested bdi (TODO: has details), along with the much smaller io-queues, the initial purpose of this function - which was to avoid all memory getting stuck in io-queues - seems to be handled. Now the problems... Trouble is that it currently does not take nr_dirty into account which in the worst case limits it to 110% of the limit. Also, I'm seeing (2.6.23-rc8-mm1) live-locks in throttle_vm_writeback() where nr_dirty + nr_unstable > thresh - which according to (1) should not happen, and will not change without explicit action. Hmm maybe the 10% is < nr_cpus * ratelimit_pages. 2 cpus, mem=128M -> ratelimit_pages ~ 512 threshold ~ 1500 so indeed: 150 < 1024. Still not conclusive but at least getting somewhere. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/