On (30/07/08 13:07), Andrew Morton didst pronounce: > On Wed, 30 Jul 2008 20:30:10 +0100 > Mel Gorman <[EMAIL PROTECTED]> wrote: > > > With Erics patch and libhugetlbfs, we can automatically back text/data[1], > > malloc[2] and stacks without source modification. Fairly soon, libhugetlbfs > > will also be able to override shmget() to add SHM_HUGETLB. That should cover > > a lot of the memory-intensive apps without source modification. > > The weak link in all of this still might be the need to reserve > hugepages and the unreliability of dynamically allocating them. > > The dynamic allocation should be better nowadays, but I've lost track > of how reliable it really is. What's our status there? >
We are a lot more reliable than we were although exact quantification is difficult because it's workload dependent. For a long time, I've been able to test bits and pieces with hugepages by allocating the pool at the time I needed it even after days of uptime. Previously this required a reboot. I've also been able to use the dynamic hugepage pool resizing effectively and we track how much it is succeeding and failing in /proc/vmstat (see the htlb fields) to watch for problems. Between that and /proc/pagetypeinfo, I am expecting to be able to identify availablilty problems. As an administrator can now set a minimum pool size and the maximum size of the pool (nr_hugepages and nr_overcommit_hugepages), the configuration difficulties should be relaxed. If it is found that anti-fragmentation can be broken down and pool resizing starts failing after X amount of time on Y workloads, there is still the option of using movablecore=BiggestPoolSizeIWillEverNeed and writing 1 to /proc/sys/vm/hugepages_treat_as_movable so the hugepage pool can grow/shrink reliably there. Overall, it's in pretty good shape. To be fair, one snag is that that swap is almost required for pool resizing to work as I never pushed to complete memory compaction (http://lwn.net/Articles/238837/). Hence, we depend on the workload to have lots of filesystem-backed data for lumpy-reclaim to do its job, for pool resizing to take place between batch jobs or for swap to be configured even if it's just for the duration of a pool resize. -- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-dev
