> sigh.. I've been hassled a lot by the possible disharmonies between > the bdi/global dirty limits. > > One example is the below graph, where the bdi dirty pages are > constantly exceeding the bdi dirty limit. The root cause is, > "(dirty + background) / 2" may be close to or even exceed > bdi_dirty_limit. When exceeded, the task will not get throttled at all at some time, and get hard throttled at other times. > http://www.kernel.org/pub/linux/kernel/people/wfg/writeback/tests/256M/ext3-2dd-1M-8p-191M-2.6.37-rc5+-2010-12-09-13-42/dirty-pages-200.png This graph is more obvious. However I'm no longer sure they are the exact graphs that are caused by "(dirty + background) / 2 > bdi_dirty_limit", which evaluates to TRUE after I do "[PATCH 02/35] writeback: safety margin for bdi stat error", which lowered bdi_dirty_limit by 1-2MB in that test case. http://www.kernel.org/pub/linux/kernel/people/wfg/writeback/tests/256M/btrfs-1dd-1M-8p-191M-2.6.37-rc5+-2010-12-09-14-35/dirty-pages-200.png Thanks, Fengguang -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
