From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx1.redhat.com (mx1.redhat.com [209.132.183.28]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ml01.01.org (Postfix) with ESMTPS id 480A121144CE3 for ; Tue, 9 Oct 2018 12:43:43 -0700 (PDT) From: Jeff Moyer Subject: Re: Problems with VM_MIXEDMAP removal from /proc//smaps References: <20181002100531.GC4135@quack2.suse.cz> Date: Tue, 09 Oct 2018 15:43:41 -0400 In-Reply-To: <20181002100531.GC4135@quack2.suse.cz> (Jan Kara's message of "Tue, 2 Oct 2018 12:05:31 +0200") Message-ID: MIME-Version: 1.0 List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: linux-nvdimm-bounces@lists.01.org Sender: "Linux-nvdimm" To: Jan Kara Cc: linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-nvdimm@lists.01.org List-ID: Jan Kara writes: > Hello, > > commit e1fb4a086495 "dax: remove VM_MIXEDMAP for fsdax and device dax" has > removed VM_MIXEDMAP flag from DAX VMAs. Now our testing shows that in the > mean time certain customer of ours started poking into /proc//smaps > and looks at VMA flags there and if VM_MIXEDMAP is missing among the VMA > flags, the application just fails to start complaining that DAX support is > missing in the kernel. The question now is how do we go about this? > > Strictly speaking, this is a userspace visible regression (as much as I > think that application poking into VMA flags at this level is just too > bold). Is there any precedens in handling similar issues with smaps which > really exposes a lot of information that is dependent on kernel > implementation details? > > I have attached a patch that is an obvious "fix" for the issue - just fake > VM_MIXEDMAP flag in smaps. But I'm open to other suggestions... Hi, Jan, I'm intrigued by the use case. Do I understand you correctly that the database in question does not intend to make data persistent from userspace? In other words, fsync/msync system calls are being issued by the database? I guess what I'm really after is a statement of requirements or expectations. It would be great if you could convince the database developer to engage in this discussion directly. Cheers, Jeff _______________________________________________ Linux-nvdimm mailing list Linux-nvdimm@lists.01.org https://lists.01.org/mailman/listinfo/linux-nvdimm