From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qg0-f47.google.com (mail-qg0-f47.google.com [209.85.192.47]) by kanga.kvack.org (Postfix) with ESMTP id E44CB6B0036 for ; Tue, 16 Sep 2014 09:52:02 -0400 (EDT) Received: by mail-qg0-f47.google.com with SMTP id i50so5570360qgf.34 for ; Tue, 16 Sep 2014 06:52:02 -0700 (PDT) Received: from mail-qa0-x235.google.com (mail-qa0-x235.google.com [2607:f8b0:400d:c00::235]) by mx.google.com with ESMTPS id v3si19112863qap.120.2014.09.16.06.52.00 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Tue, 16 Sep 2014 06:52:00 -0700 (PDT) Received: by mail-qa0-f53.google.com with SMTP id n8so5529087qaq.40 for ; Tue, 16 Sep 2014 06:52:00 -0700 (PDT) Message-ID: <54184078.4070505@redhat.com> Date: Tue, 16 Sep 2014 15:51:52 +0200 From: Paolo Bonzini MIME-Version: 1.0 Subject: Re: [PATCH] kvm: Faults which trigger IO release the mmap_sem References: <1410811885-17267-1-git-send-email-andreslc@google.com> In-Reply-To: <1410811885-17267-1-git-send-email-andreslc@google.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 8bit Sender: owner-linux-mm@kvack.org List-ID: 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 Il 15/09/2014 22:11, Andres Lagar-Cavilla ha scritto: > + if (!locked) { > + BUG_ON(npages != -EBUSY); VM_BUG_ON perhaps? > @@ -1177,9 +1210,15 @@ static int hva_to_pfn_slow(unsigned long addr, bool *async, bool write_fault, > npages = get_user_page_nowait(current, current->mm, > addr, write_fault, page); > up_read(¤t->mm->mmap_sem); > - } else > - npages = 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 = 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 = 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