On 12/06/2013 08:22 AM, Marcelo Tosatti wrote: > On Thu, Dec 05, 2013 at 11:30:27PM +0800, Xiao Guangrong wrote: >> In some cases, the lockless walker will do endless-walking on desc and >> without rewalk, consider this case: >> >> there are two descs: desc1 and desc2 who is pointed by desc1->next： >> desc1->next = desc2. >> >> CPU 0 CPU 1 >> >> lockless walk on desc1 >> deleting desc1 from the rmap >> lockless walk on desc2 (desc1->next) >> delete desc2 from the rmap >> add desc1 >> add desc2, then desc2->next = desc1 >> >> lockless walk on desc1 >> delete desc2 >> delete desc1 >> add desc2 >> add desc1; the desc1->next = desc2 >> lockless walk on desc2 >> >> …… >> >> Then, the walker is endlessly walking on desc1 and desc2 without any rewalk. > > The counter can be local to the walker. If its more than maximum rmap > size, break. > > (but still, please consider carefully whether lockless list walking is > really necessary or can be avoided). Yep, Marcelo, you're right. After thinking more, i do not have any idea to simplify this. Your approach (lockless on the first level) seems a better solution. Will do it based on that ways. Thanks! -- 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
