Messages in this thread | | | From | Andy Lutomirski <> | Date | Mon, 17 Dec 2012 14:01:05 -0800 | Subject | Re: [PATCH v2] mm: Downgrade mmap_sem before locking or populating on mmap |
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On Sun, Dec 16, 2012 at 7:29 PM, Michel Lespinasse <walken@google.com> wrote: > On Sun, Dec 16, 2012 at 10:05 AM, Andy Lutomirski <luto@amacapital.net> wrote: >> On Sun, Dec 16, 2012 at 4:39 AM, Michel Lespinasse <walken@google.com> wrote: >>> I think this could be done by extending the mlock work I did as part >>> of v2.6.38-rc1. The commit message for >>> c explains the idea; basically >>> mlock() was split into do_mlock() which just sets the VM_LOCKED flag >>> on vmas as needed, and do_mlock_pages() which goes through a range of >>> addresses and actually populates/mlocks each individual page that is >>> part of a VM_LOCKED vma. >> >> Doesn't this have the same problem? It holds mmap_sem for read for a >> long time, and if another writer comes in then r/w starvation >> prevention will kick in. > > Well, my point is that do_mlock_pages() doesn't need to hold the > mmap_sem read side for a long time. It currently releases it when > faulting a page requires a disk read, and could conceptually release > it more often if needed.
I can't find this code. It looks like do_mlock_pages calls __mlock_vma_pages_range, which calls __get_user_pages, which makes its way to __do_fault, which doesn't seem to drop mmap_sem.
--Andy
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