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@xxxxxxxxxx> 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@xxxxxxxxxx> 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. -- Gleb. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
