Messages in this thread | | | Subject | Re: [linux-next: Tree for Jun 1] __khugepaged_exit rwsem_down_write_failed lockup | From | Vlastimil Babka <> | Date | Wed, 8 Jun 2016 10:19:03 +0200 |
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On 06/03/2016 05:10 PM, Andrea Arcangeli wrote: > Hello Michal, > > CC'ed Hugh, > > On Fri, Jun 03, 2016 at 04:46:00PM +0200, Michal Hocko wrote: >> What do you think about the external dependencies mentioned above. Do >> you think this is a sufficient argument wrt. occasional higher >> latencies? > > It's a tradeoff and both latencies would be short and uncommon so it's > hard to tell.
Shouldn't it be possible to do a mmput() before the hugepage allocation, and then again mmget_not_zero()? That way it's no longer a tradeoff?
> There's also mmput_async for paths that may care about mmput > latencies. Exit itself cannot use it, it's mostly for people taking > the mm_users pin that may not want to wait for mmput to run. It also > shouldn't happen that often, it's a slow path. > > The whole model inherited from KSM is to deliberately depend only on > the mmap_sem + test_exit + mm_count, and never on mm_users, which to > me in principle doesn't sound bad. I consider KSM version a > "finegrined" implementation but I never thought it would be a problem > to wait a bit in exit() in case the slow path hits. I thought it was > more of a problem if exit() runs, the parent then start a new task but > the memory wasn't freed yet. > > So I would suggest Hugh to share his view on the down_write/up_write > that may temporarily block mmput (until the next test_exit bailout > point) vs higher latency in reaching exit_mmap for a real exit(2) that > would happen with the proposed change. > > Thanks! > Andrea > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo@kvack.org. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a> >
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