Hi, i have recently been playing with an old idea (originally in grsecurity for security reasons) to change the policy from zero on allocate to zero after free in the linux page allocator. My concern is that linux leaves a lot of waste in the physical memory unlike Windows which per default zeros pages after they are freed. I have run some tests and I can confirm some old results that a hardware Linux machine is approximately 2-3% slower with zero after free on big compilation jobs. This might be due to either the fact that pages are only zeroed on allocate if GFP_ZERO is set or due to caching benefits. However, in a virtual machine I have not observed the above slow down to that extend while the benefit of zero after free in a virtualisation environment is obvious: 1) zero pages can easily be merged by ksm or other technique. 2) zero (dup) pages are a lot faster to transfer in case of migration. Therefore I would like to hear your thoughts if it would be a good idea to change the strategy in the Linux kernel from zero on allocate to zero after free automatically if the 'hypervisor' cpu feature is set? Or even have another technique to tell a linux guest that ksm is running on the host. If this is not feasible can someone think of a kernel module / userspace program that zeroes out unused pages periodically. Peter -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
