Messages in this thread | | | Date | Tue, 16 Sep 2014 20:29:13 +0200 | From | Paolo Bonzini <> | Subject | Re: [PATCH] kvm: Faults which trigger IO release the mmap_sem |
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Il 16/09/2014 18:52, Andres Lagar-Cavilla ha scritto: > Was this: > > down_read(&mm->mmap_sem); > npages = get_user_pages(NULL, mm, addr, 1, 1, 0, NULL, NULL); > up_read(&mm->mmap_sem); > > the intention rather than get_user_pages_fast?
I meant the intention of the original author, not yours.
> By that point in the call chain I felt comfortable dropping the _fast. > All paths that get there have already tried _fast (and some have tried > _NOWAIT).
Yes, understood.
> I think a first patch should introduce kvm_get_user_page_retry ("Retry a > fault after a gup with FOLL_NOWAIT.") and the second would add > FOLL_TRIED ("This properly relinquishes mmap semaphore if the > filemap/swap has to wait on page lock (and retries the gup to completion > after that"). > > That's not what FOLL_TRIED does. The relinquishing of mmap semaphore is > done by this patch minus the FOLL_TRIED bits. FOLL_TRIED will let the > fault handler (e.g. filemap) know that we've been there and waited on > the IO already, so in the common case we won't need to redo the IO.
Yes, that's not what FOLL_TRIED does. But it's the difference between get_user_pages and kvm_get_user_page_retry, right?
Paolo
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