linux-kernel - Re: [RFC PATCH v3] ceph: add new obj copy OSD Op

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Date:   Mon, 18 Nov 2019 14:05:51 +0000
From:   Luis Henriques <lhenriques@...e.com>
To:     Jeff Layton <jlayton@...nel.org>
Cc:     Sage Weil <sage@...hat.com>, Ilya Dryomov <idryomov@...il.com>,
        "Yan, Zheng" <zyan@...hat.com>,
        Gregory Farnum <gfarnum@...hat.com>,
        ceph-devel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v3] ceph: add new obj copy OSD Op

On Mon, Nov 18, 2019 at 08:12:39AM -0500, Jeff Layton wrote:
> On Mon, 2019-11-18 at 12:09 +0000, Luis Henriques wrote:
> > Hi,
> > 
> > Before going ahead with a pull-request for ceph I would like to make sure
> > we're all on the same page regarding the final fix for this problem.
> > Thus, following this email, I'm sending 2 patches: one for ceph OSDs and
> > the another for the kernel client.
> > 
> > * osd: add new 'copy-from-notrunc' operation
> >   This patch shall be applied to ceph master after reverting commit
> >   ba152435fd85 ("osd: add flag to prevent truncate_seq copy in copy-from
> >   operation").  It adds a new operation that will be exactly the same as
> >   the original 'copy-from' operation, but with the extra 2 parameters
> >   (truncate_{seq,size})
> > 
> > * ceph: switch copy_file_range to 'copy-from-notrunc' operation
> >   This will make the kernel client use the new OSD op in
> >   copy_file_range.  One extra thing that could probably be added is
> >   changing the mount options to NOCOPYFROM if the first call to
> >   ceph_osdc_copy_from() fails.
> > 
> 
> I probably wouldn't change the mount options to be different from what
> was initially specified. How about just disable copy_file_range
> internally for that superblock, and then pr_notice a message that says
> that copy_file_range is being autodisabled. If they mount with '-o
> nocopyfrom' that will make the warning go away.

Ok, that makes sense.  I'll include this in the next rev, which will
probably be sent only after the pull-request for ceph goes in (assuming
the OSD patch won't need any major rework).

> > Does this look good, or did I missed something from the previous
> > discussion?
> > 
> > (One advantage of this approach: the OSD patch can be easily backported!)
> > 
> 
> Yep, I think this looks like a _much_ simpler approach to the problem.

Agreed!

Cheers,
--
Luís