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? Andres > > -- > Gleb. -- Andres Lagar-Cavilla | Google Kernel Team | andreslc@xxxxxxxxxx -- 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
