From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qg0-f43.google.com (mail-qg0-f43.google.com [209.85.192.43]) by kanga.kvack.org (Postfix) with ESMTP id AD8186B0036 for ; Tue, 16 Sep 2014 14:29:57 -0400 (EDT) Received: by mail-qg0-f43.google.com with SMTP id a108so362372qge.16 for ; Tue, 16 Sep 2014 11:29:57 -0700 (PDT) Received: from mx1.redhat.com (mx1.redhat.com. [209.132.183.28]) by mx.google.com with ESMTPS id c20si20063451qax.63.2014.09.16.11.29.55 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 16 Sep 2014 11:29:56 -0700 (PDT) Message-ID: <54188179.7010705@redhat.com> Date: Tue, 16 Sep 2014 20:29:13 +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> <54184078.4070505@redhat.com> In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Andres Lagar-Cavilla Cc: 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 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 -- 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