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 533CF2119C8B2 for ; Wed, 12 Dec 2018 09:50:52 -0800 (PST) Date: Wed, 12 Dec 2018 12:50:47 -0500 From: Mike Snitzer Subject: Re: Snapshot target and DAX-capable devices Message-ID: <20181212175047.GA24962@redhat.com> References: <20180828075025.GA17756@quack2.suse.cz> <20180828175630.GA1197@redhat.com> <20180830093028.GC1767@quack2.suse.cz> <20180830184907.GA14867@redhat.com> <20180830233809.GH1572@dastard> <20180831094255.GB11622@quack2.suse.cz> <167a3303a01.11a848ab768799.5161498967766415143@zoho.com> <20181212161254.GA20790@infradead.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20181212161254.GA20790@infradead.org> 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: Christoph Hellwig Cc: Jan Kara , "linux-nvdimm@lists.01.org" , chengnt , Dave Chinner , colyli , "dm-devel@redhat.com" , Mikulas Patocka , "linux-fsdevel@vger.kernel.org" List-ID: On Wed, Dec 12 2018 at 11:12am -0500, Christoph Hellwig wrote: > Does it really make sense to enhance dm-snapshot? I thought all serious > users of snapshots had moved on to dm-thinp? There are cases where dm-snapshot is still useful for people. But those are very niche users. I'm not opposed to others proposing enhancements for dm-snapshot in general but it is definitely not a priority (Google's dm-bow is an example of a case where dm-snapshot may get extended to fulfill google's needs). But for this specific DAX case, I can only assume efforts to prop up dm-snapshot like this are born out of legacy use-cases. The reality is getting DAX to work with dm-snapshot is pretty involved (due to mmap, etc). This thread got into a lot of the details: https://www.redhat.com/archives/dm-devel/2018-August/msg00211.html So any new attempt to reintroduce DAX support to dm-snapshot (or any more complex DM target) will have a very high bar. One that requires much more extensive mm and block (interlock) prep work to make DAX safe. Mike _______________________________________________ Linux-nvdimm mailing list Linux-nvdimm@lists.01.org https://lists.01.org/mailman/listinfo/linux-nvdimm