cgroup memory, blkio and the lovely swapping

Hi,

currently when one process causes heavy swapping, the responsiveness of the hole system suffers greatly. With the small memleak [1] test tool I wrote, the effect can be experienced very easily, depending on the delay the lag can become quite large. If I ensure that 10% of the RAM stay free for free memory and cache, the system never swaps to death. That works very well, but if accesses to the swap are very heavy, the system still lags on all other processes, not only the swapping one. Putting the swapping process into a blkio cgroup with little weight does not affect the io or swap io from other processes with larger weight in their group.

Maybe I'm mistaken, but wouldn't it be the easiest way to get fair swapping and control to let the pagein respect the blkio.weight value or even better add a second weight value for swapping io ?

Hi,

currently when one process causes heavy swapping, the responsiveness of the hole system suffers greatly. With the small memleak [1] test tool I wrote, the effect can be experienced very easily, depending on the delay the lag can become quite large. If I ensure that 10% of the RAM stay free for free memory and cache, the system never swaps to death. That works very well, but if accesses to the swap are very heavy, the system still lags on all other processes, not only the swapping one. Putting the swapping process into a blkio cgroup with little weight does not affect the io or swap io from other processes with larger weight in their group.

Maybe I'm mistaken, but wouldn't it be the easiest way to get fair swapping and control to let the pagein respect the blkio.weight value or even better add a second weight value for swapping io ?

Now, blkio cgroup does work only with synchronous I/O(direct I/O) and never work with swap I/O. And I don't think swap-i/o limit is a blkio matter.

Memory cgroup is now developping dirty_ratio for memory cgroup. By that, you can control the number of pages in writeback, in memory cgroup. I think it will work for you.

Now, blkio cgroup does work only with synchronous I/O(direct I/O) and never work with swap I/O. And I don't think swap-i/o limit is a blkio matter.

Memory cgroup is now developping dirty_ratio for memory cgroup. By that, you can control the number of pages in writeback, in memory cgroup. I think it will work for you.

Quoted 3 lines · On Fri, 4 Mar 2011 16:54:55 +0900 KAMEZAWA Hiroyuki…

Now, blkio cgroup does work only with synchronous I/O(direct I/O) and never work with swap I/O. And I don't think swap-i/o limit is a blkio matter.

I'm totally unsure about what subsystem it really belongs to. It is memory for sure, but disk access, which it actually affects, belongs to the blkio subsystem. Is there a technical reason why swap I/O is not run through the blkio system ?

Quoted 4 lines

Memory cgroup is now developping dirty_ratio for memory cgroup. By that, you can control the number of pages in writeback, in memory cgroup. I think it will work for you.

I'm not sure that fixes the fairness problem on swapio. Just having a larger buffer before a writeback happens will reduce seeks, but not give fair share of io in swap in. It's good to control over it on cgroup level, but i doubt it will fix the problem.

Quoted 3 lines · On Fri, 4 Mar 2011 16:54:55 +0900 KAMEZAWA Hiroyuki…

Now, blkio cgroup does work only with synchronous I/O(direct I/O) and never work with swap I/O. And I don't think swap-i/o limit is a blkio matter.

I'm totally unsure about what subsystem it really belongs to. It is memory for sure, but disk access, which it actually affects, belongs to the blkio subsystem. Is there a technical reason why swap I/O is not run through the blkio system ?

Quoted 4 lines

Memory cgroup is now developping dirty_ratio for memory cgroup. By that, you can control the number of pages in writeback, in memory cgroup. I think it will work for you.

I'm not sure that fixes the fairness problem on swapio. Just having a larger buffer before a writeback happens will reduce seeks, but not give fair share of io in swap in. It's good to control over it on cgroup level, but i doubt it will fix the problem.