From: Huaisheng HS1 Ye <yehs1@lenovo.com>
To: Mike Snitzer <snitzer@redhat.com>
Cc: Jan Kara <jack@suse.cz>,
"linux-nvdimm@lists.01.org" <linux-nvdimm@lists.01.org>,
NingTing Cheng <chengnt@lenovo.com>,
Dave Chinner <david@fromorbit.com>, colyli <colyli@suse.de>,
Christoph Hellwig <hch@infradead.org>,
"dm-devel@redhat.com" <dm-devel@redhat.com>,
Mikulas Patocka <mpatocka@redhat.com>,
"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
"Theodore Y. Ts'o" <tytso@mit.edu>
Subject: RE: [External] Re: Snapshot target and DAX-capable devices
Date: Fri, 14 Dec 2018 08:24:49 +0000 [thread overview]
Message-ID: <HK2PR03MB441871946735DE9EE714D10B92A10@HK2PR03MB4418.apcprd03.prod.outlook.com> (raw)
In-Reply-To: <20181212224321.GA2902@redhat.com>
From: Mike Snitzer <snitzer@redhat.com>
Sent: Thursday, December 13, 2018 6:43 AM
> On Wed, Dec 12 2018 at 4:15pm -0500,
> Theodore Y. Ts'o <tytso@mit.edu> wrote:
>
> > On Wed, Dec 12, 2018 at 12:50:47PM -0500, Mike Snitzer wrote:
> > > On Wed, Dec 12 2018 at 11:12am -0500,
> > > Christoph Hellwig <hch@infradead.org> 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).
> >
> > I would expect that dm-snapshot will be used quite a lot for
> > short-lived snapshots (that only live during a database backup or an
> > fsck run). I would hardly call that a "niche use case".
>
> dm-snapshot is only ~60% performant for 1 snapshot. Try to do
> additional snapshots and performance crawls to a stop (though I haven't
> reassessed performance in a while).
>
> dm-snapshot has been in Linux since before 2005, I don't know of all the
> users of it -- maybe there are a ton of users who only take a single
> temporary snapshot and we're all oblivious.
>
> Definitely not seeing many bugs against it (but it has been around
> forever). I do know that there are relatively few people showing
> interest in it. But for 4.21 I did stage a couple useful performance
> fixes:
> https://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm.git/commit/?h=dm-4.
> 21&id=61d594bb7e1cf86dca49cbc9524eb80169d9fca6
> https://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm.git/commit/?h=dm-4.
> 21&id=d1f7898c7a1b24aa9ae670f9cc21b65e730827eb
Hi Mike,
Could these two patches be applied to current code of LVM?
Although there is a difficult problem as mmap for dm-snapshot with
DAX-capable, the two patches can be used for other complex DM targets
when trying to implement DAX.
[RFC PATCH v2 2/3] dm: expand hc_map in mapped_device for lack of map
https://lkml.org/lkml/2018/11/21/273
[RFC PATCH v2 3/3] dm: expand valid types for dm-ioctl
https://lkml.org/lkml/2018/11/21/276
Cheers,
Huaisheng Ye
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next prev parent reply other threads:[~2018-12-14 8:25 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-08-27 16:07 Snapshot target and DAX-capable devices Jan Kara
2018-08-27 16:43 ` Kani, Toshi
2018-08-28 7:50 ` Jan Kara
2018-08-28 17:56 ` Mike Snitzer
2018-08-28 22:38 ` Kani, Toshi
2018-08-30 9:30 ` Jan Kara
2018-08-30 18:49 ` Mike Snitzer
2018-08-30 19:32 ` Jeff Moyer
2018-08-30 19:47 ` Mikulas Patocka
2018-08-30 19:53 ` Jeff Moyer
2018-08-30 23:38 ` Dave Chinner
2018-08-31 9:42 ` Jan Kara
2018-09-05 1:25 ` Dave Chinner
2018-12-12 16:11 ` Huaisheng Ye
2018-12-12 16:12 ` Christoph Hellwig
2018-12-12 17:50 ` Mike Snitzer
2018-12-12 19:49 ` Kani, Toshi
2018-12-12 21:15 ` Theodore Y. Ts'o
2018-12-12 22:43 ` Mike Snitzer
2018-12-14 4:11 ` [dm-devel] " Theodore Y. Ts'o
2018-12-14 8:24 ` Huaisheng HS1 Ye [this message]
2018-12-18 19:49 ` Mike Snitzer
2018-08-30 19:44 ` Mikulas Patocka
2018-08-31 10:01 ` Jan Kara
2018-08-30 22:55 ` Dave Chinner
2018-08-31 9:54 ` Jan Kara
2018-08-30 19:17 ` [dm-devel] " Jeff Moyer
2018-08-31 9:14 ` Jan Kara
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