On 11/03/2010 06:40 PM, Mandeep Singh Baines wrote:
I've created a patch which takes a slightly different approach. Instead of limiting how fast pages get reclaimed, the patch limits how fast the active list gets scanned. This should result in the active list being a better measure of the working set. I've seen fairly good results with this patch and a scan inteval of 1 centisecond. I see no thrashing when the scan interval is non-zero. I've made it a tunable because I don't know what to set the scan interval. The final patch could set the value based on HZ and some other system parameters. Maybe relate it to sched_period?
I like your approach. For file pages it looks like it could work fine, since new pages always start on the inactive file list. However, for anonymous pages I could see your patch leading to problems, because all anonymous pages start on the active list. With a scan interval of 1 centiseconds, that means there would be a limit of 3200 pages, or 12MB of anonymous memory that can be moved to the inactive list a second. I have seen systems with single SATA disks push out several times that to swap per second, which matters when someone starts up a program that is just too big to fit in memory and requires that something is pushed out. That would reduce the size of the inactive list to zero, reducing our page replacement to a slow FIFO at best, causing false OOM kills at worst. Staying with a default of 0 would of course not do anything, which would make merging the code not too useful. I believe we absolutely need to preserve the ability to evict pages quickly, when new pages are brought into memory or allocated quickly. However, speed limits are probably a very good idea once a cache has been reduced to a smaller size, or when most IO bypasses the reclaim-speed-limited cache. -- All rights reversed -- 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>