From: Dan Williams <dan.j.williams@intel.com>
To: Christoph Hellwig <hch@lst.de>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Jan Kara <jack@suse.cz>,
"Darrick J. Wong" <darrick.wong@oracle.com>,
Linux API <linux-api@vger.kernel.org>,
"linux-nvdimm@lists.01.org" <linux-nvdimm@lists.01.org>,
Dave Chinner <david@fromorbit.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
linux-xfs@vger.kernel.org, Linux MM <linux-mm@kvack.org>,
Jeff Moyer <jmoyer@redhat.com>,
Alexander Viro <viro@zeniv.linux.org.uk>,
Andy Lutomirski <luto@kernel.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
Ross Zwisler <ross.zwisler@linux.intel.com>
Subject: Re: [PATCH v6 2/5] fs, xfs: introduce S_IOMAP_SEALED
Date: Fri, 25 Aug 2017 12:44:29 -0700 [thread overview]
Message-ID: <CAPcyv4iT+7M6NwzE0WDZLZVjDYRr1Tj0_ug-Bcu9YWDtq13rXg@mail.gmail.com> (raw)
In-Reply-To: <CAPcyv4gWD7sTLdmwoX7Ce+McMvtLKhOf60e-1ax12qQs7=Qzdg@mail.gmail.com>
On Thu, Aug 24, 2017 at 11:00 PM, Dan Williams <dan.j.williams@intel.com> wrote:
> On Thu, Aug 24, 2017 at 9:13 AM, Christoph Hellwig <hch@lst.de> wrote:
>> I'm still very unhappy about the get/set flag state. What is the
>> reason you can't use/extend leases? (take a look at the fcntl
>> man page and look for Leases). A variant of the concept is what
>> the pNFS block server uses.
>
> So I think leases could potentially be extended to replace the inode
> flag. A MAP_DIRECT operation would take out a lease that is broken by
> break_layouts(). However, like the pNFS case the lease break would
> need to held off while any DMA might be in-flight. We can use an
> elevated page count as that indication as ZONE_DEVICE pages only ever
> have an elevated page count in response to get_user_pages().
>
> However, I think the only practical difference is turning an immediate
> ETXTBSY response that S_IOMAP_SEALED provides into an indefinite
> blocking wait for break_layouts() to complete. Can pNFS run
> break_layouts() in bounded time?
>
> As far I can see a lease and S_IOMAP_SEALED have the same DMA
> cancelling problem, so a lease is not better in that regard. Absent an
> overlaying protocol like pNFS, I think S_IOMAP_SEALED is cleaner
> because it fails incompatible operations outright rather than stalls
> them in break_layouts(). Were their other benefits to a lease over an
> inode flag that you had in mind for this case where the protocol is
> userspace defined? Maybe I'm thinking too small on the ways a lease
> might be extended.
At a minimum I can at least use a new lease type as an indication of
when to bail out an block-map operation with ETXTBSY, and reuse the
lease security model. That way we at least start to converge the
in-kernel lease machinery for pinning blocks with this userspace
mechanism.
next prev parent reply other threads:[~2017-08-25 19:44 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-08-23 23:48 [PATCH v6 0/5] MAP_DIRECT and block-map-atomic files Dan Williams
[not found] ` <150353211413.5039.5228914877418362329.stgit-p8uTFz9XbKj2zm6wflaqv1nYeNYlB/vhral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
2017-08-23 23:48 ` [PATCH v6 1/5] vfs: add flags parameter to ->mmap() in 'struct file_operations' Dan Williams
[not found] ` <150353211985.5039.4333061601382775843.stgit-p8uTFz9XbKj2zm6wflaqv1nYeNYlB/vhral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
2017-08-24 16:58 ` Christoph Hellwig
2017-08-24 17:42 ` Dan Williams
2017-08-23 23:48 ` [PATCH v6 2/5] fs, xfs: introduce S_IOMAP_SEALED Dan Williams
[not found] ` <150353212577.5039.14069456126848863439.stgit-p8uTFz9XbKj2zm6wflaqv1nYeNYlB/vhral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
2017-08-24 16:13 ` Christoph Hellwig
2017-08-25 6:00 ` Dan Williams
2017-08-25 19:44 ` Dan Williams [this message]
2017-08-23 23:48 ` [PATCH v6 4/5] fs, xfs: introduce MAP_DIRECT for creating block-map-atomic file ranges Dan Williams
[not found] ` <150353213655.5039.7662200155640827407.stgit-p8uTFz9XbKj2zm6wflaqv1nYeNYlB/vhral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
2017-08-24 16:11 ` Christoph Hellwig
[not found] ` <20170824161152.GB27591-jcswGhMUV9g@public.gmane.org>
2017-08-24 16:31 ` Dan Williams
2017-08-24 16:39 ` Christoph Hellwig
[not found] ` <20170824163925.GA28503-jcswGhMUV9g@public.gmane.org>
2017-08-24 20:26 ` Dan Williams
2017-08-23 23:49 ` [PATCH v6 5/5] fs, fcntl: add F_MAP_DIRECT Dan Williams
2017-08-23 23:48 ` [PATCH v6 3/5] mm: introduce mmap3 for safely defining new mmap flags Dan Williams
[not found] ` <150353213097.5039.6729469069608762658.stgit-p8uTFz9XbKj2zm6wflaqv1nYeNYlB/vhral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
2017-08-24 13:04 ` Jan Kara
2017-08-24 16:55 ` Christoph Hellwig
[not found] ` <20170824165546.GA3121-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>
2017-08-24 17:36 ` Dan Williams
[not found] ` <CAPcyv4iN0QpUSgOUvisnNQsiV1Pp=4dh7CwAV8FFj=_rFU=aug-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2017-08-25 13:00 ` Christoph Hellwig
2017-08-25 15:58 ` Kirill A. Shutemov
2017-08-25 16:02 ` Christoph Hellwig
2017-08-25 16:16 ` Kirill A. Shutemov
[not found] ` <20170825161607.6v6beg4zjktllt2z-sVvlyX1904swdBt8bTSxpkEMvNT87kid@public.gmane.org>
2017-08-25 16:19 ` Helge Deller
2017-08-25 16:56 ` Kirill A. Shutemov
2017-08-25 20:24 ` Dan Williams
[not found] ` <CAPcyv4jeZc8P+E0aHNChzy-wfNpOx3GehKck1nXqJ1b9JdydFA-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2017-08-26 7:40 ` Helge Deller
2017-08-26 15:15 ` Dan Williams
[not found] ` <CAPcyv4ic0zxQzWEipZ=1LpDC8VnmphGzVSYmrFcjOAgX7esfUw-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2017-08-26 19:50 ` Helge Deller
2017-08-26 22:46 ` Dan Williams
2017-08-26 23:56 ` Kirill A. Shutemov
2017-08-24 16:08 ` [PATCH v6 0/5] MAP_DIRECT and block-map-atomic files Christoph Hellwig
2017-08-24 16:25 ` Dan Williams
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