From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0a-002e3701.pphosted.com (mx0a-002e3701.pphosted.com [148.163.147.86]) (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 269522119681D for ; Wed, 12 Dec 2018 11:49:51 -0800 (PST) From: "Kani, Toshi" Subject: Re: Snapshot target and DAX-capable devices Date: Wed, 12 Dec 2018 19:49:25 +0000 Message-ID: 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> <20181212175047.GA24962@redhat.com> In-Reply-To: <20181212175047.GA24962@redhat.com> Content-Language: en-US Content-ID: <4214681ED56B6A43AED1CAB47BB5D7DE@NAMPRD84.PROD.OUTLOOK.COM> 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: "hch@infradead.org" , "snitzer@redhat.com" Cc: "jack@suse.cz" , "linux-nvdimm@lists.01.org" , "chengnt@lenovo.com" , "david@fromorbit.com" , "colyli@suse.de" , "dm-devel@redhat.com" , "mpatocka@redhat.com" , "linux-fsdevel@vger.kernel.org" List-ID: On Wed, 2018-12-12 at 12:50 -0500, Mike Snitzer wrote: > 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. Just to be clear, "reintroduce DAX support to dm-snapshot" is a bit misleading because there wasn't such attempt before. My original hack/change in dm-snapshot was to support non-DAX use-cases to work with DAX-capable devices. Thanks, -Toshi _______________________________________________ Linux-nvdimm mailing list Linux-nvdimm@lists.01.org https://lists.01.org/mailman/listinfo/linux-nvdimm