On Mon, 30 Jan 2012 10:16:39 -0800, Tejun Heo <tj@xxxxxxxxxx> wrote: > On Mon, Jan 30, 2012 at 12:12:18PM -0600, Christoph Lameter wrote: > > > I thought it didn't. I rememer thinking about this and determining > > > that NULL can't be allocated for dynamic addresses. Maybe I'm > > > imagining things. Anyways, if it can return NULL for valid > > > allocation, it is a bug and should be fixed. > > > > I dont see anything that would hinder an arbitrary value to be returned. > > NULL is also used for the failure case. Definitely a bug. > > Given the address translation we do and kernel image layout, I don't > think this can happen on x86. It may theoretically possible on other > archs tho. Anyways, yeah, this one needs improving. I tried setting the lower bit on all percpu ptrs, but since non-dynamic percpu vars could have odd alignments, that fails in general. > > > We don't have returned addr >= PAGE_SIZE guarantee yet but I'm fairly > > > sure that's the only acceptable direction if we want any improvement > > > in this area. > > > > The ZERO_SIZE_PTR patch would not make the situation that much worse. > > I'm not objecting to marking zero-sized allocations per-se. I'm > saying the patch is pointless at this point. It doesn't contribute > anything while giving the illusion of better error checking than we > actually do. Let's do it when it can actually work. Disagree: This patch works. It allows zero-size per-cpu allocs, like the other allocators. Nor does it fail in practice. We should do better, but the perfect is the enemy of the good. Cheers, Rusty. -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>