Messages in this thread | | | Date | Wed, 11 May 2005 21:42:24 +0100 (BST) | From | Hugh Dickins <> | Subject | Re: [openib-general] Re: [PATCH][RFC][0/4] InfiniBand userspace verbs implementation |
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On Wed, 11 May 2005, William Jordan wrote: > On 5/7/05, Hugh Dickins <hugh@veritas.com> wrote: > > > My understanding is that mlock() could in theory allow the page to be moved, > > > but that currently nothing in the kernel would actually move it. However, > > > that could change in the future to allow hot-swapping of RAM. > > > > That's my understanding too, that nothing currently does so. Aside from > > hot-swapping RAM, there's also a need to be able to migrate pages around > > RAM, either to unfragment memory allowing higher-order allocations to > > succeed more often, or to get around extreme dmamem/normal-mem/highmem > > imbalances without dedicating huge reserves. Those would more often > > succeed if uninhibited by mlock. > > If I am reading you correctly, you are saying that mlock currently > prevents pages from migrating around to unfragment memory, but > get_user_pages does not prevent this?
No, not what I meant at all. I'm saying that currently (aside from proposed patches) there is no such migration of pages; that we'd prefer to implement migration in such a way that mlock does not inhibit it (though there might prove to be strong arguments defeating that); and that get_user_pages _must_ prevent migration (and if there were already such migration, I'd be saying it _does_ prevent it).
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