Messages in this thread | | | Date | Wed, 17 Sep 2014 10:41:06 -0700 | Subject | Re: [PATCH] kvm: Faults which trigger IO release the mmap_sem | From | Andres Lagar-Cavilla <> |
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On Wed, Sep 17, 2014 at 10:21 AM, Gleb Natapov <gleb@kernel.org> wrote: > On Wed, Sep 17, 2014 at 10:13:45AM -0700, Andres Lagar-Cavilla wrote: >> On Wed, Sep 17, 2014 at 10:08 AM, Gleb Natapov <gleb@kernel.org> wrote: >> > On Wed, Sep 17, 2014 at 10:00:32AM -0700, Andres Lagar-Cavilla wrote: >> >> On Wed, Sep 17, 2014 at 4:42 AM, Gleb Natapov <gleb@kernel.org> wrote: >> >> > On Wed, Sep 17, 2014 at 01:27:14PM +0200, Radim Krčmář wrote: >> >> >> 2014-09-17 13:26+0300, Gleb Natapov: >> >> >> > For async_pf_execute() you do not need to even retry. Next guest's page fault >> >> >> > will retry it for you. >> >> >> >> >> >> Wouldn't that be a waste of vmentries? >> >> > This is how it will work with or without this second gup. Page is not >> >> > mapped into a shadow page table on this path, it happens on a next fault. >> >> >> >> The point is that the gup in the async pf completion from the work >> >> queue will not relinquish the mmap semaphore. And it most definitely >> >> should, given that we are likely looking at swap/filemap. >> >> >> > I get this point and the patch looks good in general, but my point is >> > that when _retry() is called from async_pf_execute() second gup is not >> > needed. In the original code gup is called to do IO and nothing else. >> > In your patch this is accomplished by the first gup already, so you >> > can skip second gup if pagep == nullptr. >> >> I see. However, if this function were to be used elsewhere in the >> future, then the "if pagep == NULL don't retry" semantics may not >> match the new caller's intention. Would you prefer an explicit flag? >> > We can add explicit flag whenever such caller will be added, if ever.
Ok. Patch forthcoming.
Paolo, I'm not sure the split will buy anything, because the first patch will be a one-liner (no point in the new kvm_gup_something function if the impl won't match the intended semantics of the function). But if you push back, I'll cut a v3.
Thanks all, Andres > > -- > Gleb.
-- Andres Lagar-Cavilla | Google Kernel Team | andreslc@google.com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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