on 2010-3-11 16:15, Nick Piggin wrote: > On Tue, Mar 09, 2010 at 03:25:54PM +0800, Miao Xie wrote: >> on 2010-3-9 5:46, David Rientjes wrote: >> [snip] >>>> Considering the change of task->mems_allowed is not frequent, so in this patch, >>>> I use two variables as a tag to indicate whether task->mems_allowed need be >>>> update or not. And before setting the tag, cpuset caches the new mask of every >>>> task at its task_struct. >>>> >>> >>> So what exactly is the benefit of 58568d2 from last June that caused this >>> issue to begin with? It seems like this entire patchset is a revert of >>> that commit. So why shouldn't we just revert that one commit and then add >>> the locking and updating necessary for configs where >>> MAX_NUMNODES > BITS_PER_LONG on top? >> >> I worried about the consistency of task->mempolicy with task->mems_allowed for >> configs where MAX_NUMNODES <= BITS_PER_LONG. >> >> The problem that I worried is fowllowing: >> When the kernel allocator allocates pages for tasks, it will access task->mempolicy >> first and get the allowed node, then check whether that node is allowed by >> task->mems_allowed. >> >> But, Without this patch, ->mempolicy and ->mems_allowed is not updated at the same >> time. the kernel allocator may access the inconsistent information of ->mempolicy >> and ->mems_allowed, sush as the allocator gets the allowed node from old mempolicy, >> but checks whether that node is allowed by new mems_allowed which does't intersect >> old mempolicy. >> >> So I made this patchset. > > I like your focus on keeping the hotpath light, but it is getting a bit > crazy. I wonder if it wouldn't be better just to teach those places that > matter to retry on finding an inconsistent nodemask? The only failure > case to worry about is getting an empty nodemask, isn't it? > Ok, I try to make a new patch by using seqlock. Miao -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>