On 05/15/2015 02:53 PM, Ralf Baechle wrote:
On Thu, May 14, 2015 at 06:34:43PM -0700, Leonid Yegoshin wrote: The order 1 allocation for the PGD are concerning me a little. On a system under even moderate memory pressure that might become a bit of a reliability or performance issue. With 4kB pages we already need order 1 or even 2 allocations for the allocation of the stack and some folks have reported that to be an issue so we may have to start using the PUD for very large VA spaces. Ralf
I don't think it is an issue here - people, who wants to exercise 256 TERABAIT of memory PER PROCESS may even doesn't note that they have PGD = 2 pages. It is definitely not for systems with 4GB physmemory.
I also recommend for low memory to look into CONFIG_COMPACTION, it may be a great help for them here, look into mm/vmscan.c, in_reclaim_compaction().
Besides that, I defined this feature for 16KB and 64KB pages only, not for 4KB.
