On Fri, Jun 24, 2011 at 03:44:53PM +0100, Mel Gorman wrote: > (Built this time and passed a basic sniff-test.) > > During allocator-intensive workloads, kswapd will be woken frequently > causing free memory to oscillate between the high and min watermark. > This is expected behaviour. Unfortunately, if the highest zone is > small, a problem occurs. > > This seems to happen most with recent sandybridge laptops but it's > probably a co-incidence as some of these laptops just happen to have > a small Normal zone. The reproduction case is almost always during > copying large files that kswapd pegs at 100% CPU until the file is > deleted or cache is dropped. > > The problem is mostly down to sleeping_prematurely() keeping kswapd > awake when the highest zone is small and unreclaimable and compounded > by the fact we shrink slabs even when not shrinking zones causing a lot > of time to be spent in shrinkers and a lot of memory to be reclaimed. > > Patch 1 corrects sleeping_prematurely to check the zones matching > the classzone_idx instead of all zones. > > Patch 2 avoids shrinking slab when we are not shrinking a zone. > > Patch 3 notes that sleeping_prematurely is checking lower zones against > a high classzone which is not what allocators or balance_pgdat() > is doing leading to an artifical believe that kswapd should be > still awake. > > Patch 4 notes that when balance_pgdat() gives up on a high zone that the > decision is not communicated to sleeping_prematurely() > > This problem affects 2.6.38.8 for certain and is expected to affect > 2.6.39 and 3.0-rc4 as well. If accepted, they need to go to -stable > to be picked up by distros and this series is against 3.0-rc4. I've > cc'd people that reported similar problems recently to see if they > still suffer from the problem and if this fixes it. > Good! This patch solved the problem. But there is still a mystery. In log, we could see excessive shrink_slab calls. And as you know, we had merged patch which adds cond_resched where last of the function in shrink_slab. So other task should get the CPU and we should not see 100% CPU of kswapd, I think. Do you have any idea about this? > mm/vmscan.c | 59 +++++++++++++++++++++++++++++++++++------------------------ > 1 files changed, 35 insertions(+), 24 deletions(-) > > -- > 1.7.3.4 > -- Kind regards, Minchan Kim -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>