On Fri, 2014-02-21 at 13:24 -0800, Linus Torvalds wrote: > On Fri, Feb 21, 2014 at 12:57 PM, Davidlohr Bueso <davidl...@hp.com> wrote: > > > > Btw, one concern I had is regarding seqnum overflows... if such > > scenarios should happen we'd end up potentially returning bogus vmas and > > getting bus errors and other sorts of issues. So we'd have to flush the > > caches, but, do we care? I guess on 32bit systems it could be a bit more > > possible to trigger given enough forking. > > I guess we should do something like > > if (unlikely(!++seqnum)) > flush_vma_cache() > > just to not have to worry about it. > > And we can either use a "#ifndef CONFIG_64BIT" to disable it for the > 64-bit case (because no, we really don't need to worry about overflow > in 64 bits ;), or just decide that a 32-bit sequence number actually > packs better in the structures, and make it be an "u32" even on 64-bit > architectures? > > It looks like a 32-bit sequence number might pack nicely next to the > > unsigned brk_randomized:1;
And probably specially so for structures like task and mm. I hadn't considered the benefits of packing vs overflowing. So we can afford flushing all tasks's vmacache every 4 billion forks. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
