On Thu, Jun 20, 2013 at 7:48 AM, Christoph Lameter <cl@xxxxxxxxx> wrote: > There is no way that user space can initiate a page pin right now. Perf is > pinning the page from the kernel. Similarly the IB subsystem pins memory > meeded for device I/O. Christoph, your argument would be a lot more convincing if you stopped repeating this nonsense. Sure, in a strict sense, it might be true that the IB subsystem in the kernel is the code that actually pins memory, but given that unprivileged userspace can tell the kernel to pin arbitrary parts of its memory for any amount of time, is that relevant? And in fact taking your "initiate" word choice above, I don't even think your statement is true -- userspace initiates the pinning by, for example, doing an IB memory registration (libibverbs ibv_reg_mr() call), which turns into a system call, which leads to the kernel trying to pin pages. The pages aren't unpinned until userspace unregisters the memory (or causes a cleanup by closing the context fd). Here's an argument by analogy. Would it make any sense for me to say userspace can't mlock memory, because only the kernel can set VM_LOCKED on a vma? Of course not. Userspace has the mlock() system call, and although the actual work happens in the kernel, we clearly want to be able to limit the amount of memory locked by the kernel ON BEHALF OF USERSPACE. - R. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>