From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paolo Bonzini Subject: Re: [PATCH] kvm: Faults which trigger IO release the mmap_sem Date: Tue, 16 Sep 2014 15:51:52 +0200 Message-ID: <54184078.4070505@redhat.com> References: <1410811885-17267-1-git-send-email-andreslc@google.com> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: quoted-printable To: Andres Lagar-Cavilla , Gleb Natapov , Rik van Riel , Peter Zijlstra , Mel Gorman , Andy Lutomirski , Andrew Morton , Andrea Arcangeli , Sasha Levin , Jianyu Zhan , Paul Cassella , Hugh Dickins , Peter Feiner , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Return-path: In-Reply-To: <1410811885-17267-1-git-send-email-andreslc@google.com> Sender: owner-linux-mm@kvack.org List-Id: kvm.vger.kernel.org Il 15/09/2014 22:11, Andres Lagar-Cavilla ha scritto: > + if (!locked) { > + BUG_ON(npages !=3D -EBUSY); VM_BUG_ON perhaps? > @@ -1177,9 +1210,15 @@ static int hva_to_pfn_slow(unsigned long addr, b= ool *async, bool write_fault, > npages =3D get_user_page_nowait(current, current->mm, > addr, write_fault, page); > up_read(¤t->mm->mmap_sem); > - } else > - npages =3D get_user_pages_fast(addr, 1, write_fault, > - page); > + } else { > + /* > + * By now we have tried gup_fast, and possible async_pf, and we > + * are certainly not atomic. Time to retry the gup, allowing > + * mmap semaphore to be relinquished in the case of IO. > + */ > + npages =3D kvm_get_user_page_retry(current, current->mm, addr, > + write_fault, page); This is a separate logical change. Was this: down_read(&mm->mmap_sem); npages =3D 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 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"). Apart from this, the patch looks good. The mm/ parts are minimal, so I think it's best to merge it through the KVM tree with someone's Acked-by. Paolo -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org