On Tue, 28 Sep 2010 07:35 -0500, "Christoph Lameter" <cl@xxxxxxxxx> wrote: > > The problem we saw was purely with file caching. The application wasn't > > actually allocating much memory itself, but it was reading lots of files > > from disk (via mmap'ed memory mostly), and as most people would, we > > expected that data would be cached in memory to reduce future reads from > > disk. That was not happening. > > Obviously and you have stated that numerous times. Problem that the use > of > a remote memory will reduced performance of reads so the OS (with > zone_reclaim=1) defaults to the use of local memory and favors reclaim of > local memory over the allocation from the remote node. This is fine if > you have multiple applications running on both nodes because then each > application will get memory local to it and therefore run faster. That > does not work with a single app that only allocates from one node. Is this what's happening, or is IO actually coming from disk in preference to the remote node? I can certainly see the logic behind preferring to reclaim the local node if that's all that's happening - though the OS should be allocating the different tasks more evenly across the nodes in that case. > Control over memory allocations over the various nodes under NUMA > for a process can occur via the numactl ctl or the libnuma C apis. > > F.e.e > > numactl --interleave ... command > > will address that issue for a specific command that needs to go Gosh what a pain. While it won't kill us too much to add to our startup, it does feel a lot like the tail is wagging the dog from here still. A task that doesn't ask for anything special should get sane defaults, and the cost of data from the other node should be a lot less than the cost of the same data from spinning rust. Bron. -- Bron Gondwana brong@xxxxxxxxxxx -- 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>