Messages in this thread |  | | Subject | Re: [PATCH] mm: per-thread vma caching | From | Davidlohr Bueso <> | Date | Fri, 21 Feb 2014 20:55:55 -0800 |
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On Fri, 2014-02-21 at 13:24 -0800, Linus Torvalds wrote: > On Fri, Feb 21, 2014 at 12:57 PM, Davidlohr Bueso <davidlohr@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.
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