On Tue, 23 Mar 2010, Mel Gorman wrote: > I was having some sort of fit when I wrote that obviously. Try this on > for size > > The fragmentation index may indicate that a failure is due to external > fragmentation but after a compaction run completes, it is still possible > for an allocation to fail. Ok. > > > fail. There are two obvious reasons as to why > > > > > > o Page migration cannot move all pages so fragmentation remains > > > o A suitable page may exist but watermarks are not met > > > > > > In the event of compaction and allocation failure, this patch prevents > > > compaction happening for a short interval. It's only recorded on the > > > > compaction is "recorded"? deferred? > > > > deferred makes more sense. > > What I was thinking at the time was that compact_resume was stored in struct > zone - i.e. that is where it is recorded. Ok adding a dozen or more words here may be useful. > > > preferred zone but that should be enough coverage. This could have been > > > implemented similar to the zonelist_cache but the increased size of the > > > zonelist did not appear to be justified. > > > > > @@ -1787,6 +1787,9 @@ __alloc_pages_direct_reclaim(gfp_t gfp_mask, unsigned int order, > > > */ > > > count_vm_event(COMPACTFAIL); > > > > > > + /* On failure, avoid compaction for a short time. */ > > > + defer_compaction(preferred_zone, jiffies + HZ/50); > > > + > > > > 20ms? How was that interval determined? > > > > Matches the time the page allocator would defer to an event like > congestion. The choice is somewhat arbitrary. Ideally, there would be > some sort of event that would re-enable compaction but there wasn't an > obvious candidate so I used time. There are frequent uses of HZ/10 as well especially in vmscna.c. A longer time may be better? HZ/50 looks like an interval for writeout. But this is related to reclaim? backing-dev.h <global> 283 long congestion_wait(int sync, long timeout); 1 backing-dev.c <global> 762 EXPORT_SYMBOL(congestion_wait); 2 usercopy_32.c __copy_to_user_ll 754 congestion_wait(BLK_RW_ASYNC, HZ/50); 3 pktcdvd.c pkt_make_request 2557 congestion_wait(BLK_RW_ASYNC, HZ); 4 dm-crypt.c kcryptd_crypt_write_convert 834 congestion_wait(BLK_RW_ASYNC, HZ/100); 5 file.c fat_file_release 137 congestion_wait(BLK_RW_ASYNC, HZ/10); 6 journal.c reiserfs_async_progress_wait 990 congestion_wait(BLK_RW_ASYNC, HZ / 10); 7 kmem.c kmem_alloc 61 congestion_wait(BLK_RW_ASYNC, HZ/50); 8 kmem.c kmem_zone_alloc 117 congestion_wait(BLK_RW_ASYNC, HZ/50); 9 xfs_buf.c _xfs_buf_lookup_pages 343 congestion_wait(BLK_RW_ASYNC, HZ/50); a backing-dev.c congestion_wait 751 long congestion_wait(int sync, long timeout) b memcontrol.c mem_cgroup_force_empty 2858 congestion_wait(BLK_RW_ASYNC, HZ/10); c page-writeback.c throttle_vm_writeout 674 congestion_wait(BLK_RW_ASYNC, HZ/10); d page_alloc.c __alloc_pages_high_priority 1753 congestion_wait(BLK_RW_ASYNC, HZ/50); e page_alloc.c __alloc_pages_slowpath 1924 congestion_wait(BLK_RW_ASYNC, HZ/50); f vmscan.c shrink_inactive_list 1136 congestion_wait(BLK_RW_ASYNC, HZ/10); g vmscan.c shrink_inactive_list 1220 congestion_wait(BLK_RW_ASYNC, HZ/10); h vmscan.c do_try_to_free_pages 1837 congestion_wait(BLK_RW_ASYNC, HZ/10); i vmscan.c balance_pgdat 2161 congestion_wait(BLK_RW_ASYNC, HZ/10); -- 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/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>