On 09/07/2016 08:36 PM, Xiao Guangrong wrote:>> The user will see two VMAs in their output: >> >> A: 0x1000->0x2000 >> C: 0x1000->0x3000 >> >> Will it confuse them to see the same virtual address range twice? Or is >> there something preventing that happening that I'm missing? >> > > You are right. Nothing can prevent it. > > However, it is not easy to handle the case that the new VMA overlays > with the old VMA > already got by userspace. I think we have some choices: > 1: One way is completely skipping the new VMA region as current kernel > code does but i > do not think this is good as the later VMAs will be dropped. > > 2: show the un-overlayed portion of new VMA. In your case, we just show > the region > (0x2000 -> 0x3000), however, it can not work well if the VMA is a new > created > region with different attributions. > > 3: completely show the new VMA as this patch does. > > Which one do you prefer? I'd be willing to bet that #3 will break *somebody's* tooling. Addresses going backwards is certainly screwy. Imagine somebody using smaps to search for address holes and doing hole_size=0x1000-0x2000. #1 can lies about there being no mapping in place where there there may have _always_ been a mapping and is very similar to the bug you were originally fixing. I think that throws it out. #2 is our best bet, I think. It's unfortunately also the most code. It's also a bit of a fib because it'll show a mapping that never actually existed, but I think this is OK. I'm not sure what the downside is that you're referring to, though. Can you explain? -- 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>