From: Dave Chinner <email@example.com> To: Dan Williams <firstname.lastname@example.org> Cc: "email@example.com" <firstname.lastname@example.org>, "email@example.com" <firstname.lastname@example.org>, "email@example.com" <firstname.lastname@example.org>, "email@example.com" <firstname.lastname@example.org>, "email@example.com" <firstname.lastname@example.org>, "email@example.com" <firstname.lastname@example.org>, "email@example.com" <firstname.lastname@example.org>, "email@example.com" <firstname.lastname@example.org>, "email@example.com" <firstname.lastname@example.org>, "email@example.com" <firstname.lastname@example.org>, "email@example.com" <firstname.lastname@example.org>, "email@example.com" <firstname.lastname@example.org>, "email@example.com" <firstname.lastname@example.org> Subject: Re: [Ocfs2-devel] Question about the "EXPERIMENTAL" tag for dax in XFS Date: Sat, 27 Feb 2021 08:27:48 +1100 [thread overview] Message-ID: <20210226212748.GY4662@dread.disaster.area> (raw) In-Reply-To: <CAPcyv4iDefA3Y0wUW=p080SYAsM_2TPJba-V-sxdK_BeJMkmsw@mail.gmail.com> On Fri, Feb 26, 2021 at 12:59:53PM -0800, Dan Williams wrote: > On Fri, Feb 26, 2021 at 12:51 PM Dave Chinner <email@example.com> wrote: > > > > On Fri, Feb 26, 2021 at 11:24:53AM -0800, Dan Williams wrote: > > > On Fri, Feb 26, 2021 at 11:05 AM Darrick J. Wong <firstname.lastname@example.org> wrote: > > > > > > > > On Fri, Feb 26, 2021 at 09:45:45AM +0000, email@example.com wrote: > > > > > Hi, guys > > > > > > > > > > Beside this patchset, I'd like to confirm something about the > > > > > "EXPERIMENTAL" tag for dax in XFS. > > > > > > > > > > In XFS, the "EXPERIMENTAL" tag, which is reported in waring message > > > > > when we mount a pmem device with dax option, has been existed for a > > > > > while. It's a bit annoying when using fsdax feature. So, my initial > > > > > intention was to remove this tag. And I started to find out and solve > > > > > the problems which prevent it from being removed. > > > > > > > > > > As is talked before, there are 3 main problems. The first one is "dax > > > > > semantics", which has been resolved. The rest two are "RMAP for > > > > > fsdax" and "support dax reflink for filesystem", which I have been > > > > > working on. > > > > > > > > <nod> > > > > > > > > > So, what I want to confirm is: does it means that we can remove the > > > > > "EXPERIMENTAL" tag when the rest two problem are solved? > > > > > > > > Yes. I'd keep the experimental tag for a cycle or two to make sure that > > > > nothing new pops up, but otherwise the two patchsets you've sent close > > > > those two big remaining gaps. Thank you for working on this! > > > > > > > > > Or maybe there are other important problems need to be fixed before > > > > > removing it? If there are, could you please show me that? > > > > > > > > That remains to be seen through QA/validation, but I think that's it. > > > > > > > > Granted, I still have to read through the two patchsets... > > > > > > I've been meaning to circle back here as well. > > > > > > My immediate concern is the issue Jason recently highlighted  with > > > respect to invalidating all dax mappings when / if the device is > > > ripped out from underneath the fs. I don't think that will collide > > > with Ruan's implementation, but it does need new communication from > > > driver to fs about removal events. > > > > > > : http://lore.kernel.org/r/CAPcyv4i+PZhYZiePf2PaH0dT5jDfkmkDX-3usQy1fAhf6LPyfw@mail.gmail.com > > > > Oh, yay. > > > > The XFS shutdown code is centred around preventing new IO from being > > issued - we don't actually do anything about DAX mappings because, > > well, I don't think anyone on the filesystem side thought they had > > to do anything special if pmem went away from under it. > > > > My understanding -was- that the pmem removal invalidates > > all the ptes currently mapped into CPU page tables that point at > > the dax device across the system. THe vmas that manage these > > mappings are not really something the filesystem really manages, > > but a function of the mm subsystem. What the filesystem cares about > > is that it gets page faults triggered when a change of state occurs > > so that it can remap the page to it's backing store correctly. > > > > IOWs, all the mm subsystem needs to when pmem goes away is clear the > > CPU ptes, because then when then when userspace tries to access the > > mapped DAX pages we get a new page fault. In processing the fault, the > > filesystem will try to get direct access to the pmem from the block > > device. This will get an ENODEV error from the block device because > > because the backing store (pmem) has been unplugged and is no longer > > there... > > > > AFAICT, as long as pmem removal invalidates all the active ptes that > > point at the pmem being removed, the filesystem doesn't need to > > care about device removal at all, DAX or no DAX... > > How would the pmem removal do that without walking all the active > inodes in the fs at the time of shutdown and call > unmap_mapping_range(inode->i_mapping, 0, 0, 1)? Which then immediately ends up back at the vmas that manage the ptes to unmap them. Isn't finding the vma(s) that map a specific memory range exactly what the rmap code in the mm subsystem is supposed to address? Cheers, Dave. -- Dave Chinner firstname.lastname@example.org _______________________________________________ Ocfs2-devel mailing list Ocfs2email@example.com https://oss.oracle.com/mailman/listinfo/ocfs2-devel
next prev parent reply other threads:[~2021-02-26 21:28 UTC|newest] Thread overview: 73+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-02-26 0:20 [Ocfs2-devel] [PATCH v2 00/10] fsdax, xfs: Add reflink&dedupe support for fsdax Shiyang Ruan 2021-02-26 0:20 ` [Ocfs2-devel] [PATCH v2 01/10] fsdax: Factor helpers to simplify dax fault code Shiyang Ruan 2021-03-03 9:13 ` Christoph Hellwig 2021-02-26 0:20 ` [Ocfs2-devel] [PATCH v2 02/10] fsdax: Factor helper: dax_fault_actor() Shiyang Ruan 2021-03-03 9:28 ` Christoph Hellwig 2021-03-12 9:01 ` ruansy.fnst 2021-02-26 0:20 ` [Ocfs2-devel] [PATCH v2 03/10] fsdax: Output address in dax_iomap_pfn() and rename it Shiyang Ruan 2021-02-26 0:20 ` [Ocfs2-devel] [PATCH v2 05/10] fsdax: Replace mmap entry in case of CoW Shiyang Ruan 2021-03-03 9:30 ` Christoph Hellwig 2021-03-03 9:41 ` ruansy.fnst 2021-03-03 9:44 ` Christoph Hellwig 2021-03-03 9:48 ` Christoph Hellwig 2021-02-26 0:20 ` [Ocfs2-devel] [PATCH v2 08/10] fsdax: Dedup file range to use a compare function Shiyang Ruan 2021-02-26 8:28 ` Shiyang Ruan 2021-03-03 8:20 ` Joe Perches 2021-03-03 8:45 ` ruansy.fnst 2021-03-03 9:04 ` Joe Perches 2021-03-03 9:39 ` hch 2021-03-03 9:46 ` ruansy.fnst 2021-03-04 5:42 ` [Ocfs2-devel] [RESEND PATCH v2.1 " Shiyang Ruan 2021-02-26 0:20 ` [Ocfs2-devel] [PATCH v2 09/10] fs/xfs: Handle CoW for fsdax write() path Shiyang Ruan 2021-03-03 9:43 ` Christoph Hellwig 2021-03-03 9:57 ` ruansy.fnst 2021-03-03 10:43 ` Christoph Hellwig 2021-03-04 1:35 ` ruansy.fnst 2021-02-26 0:20 ` [Ocfs2-devel] [PATCH v2 10/10] fs/xfs: Add dedupe support for fsdax Shiyang Ruan 2021-02-26 9:45 ` [Ocfs2-devel] Question about the "EXPERIMENTAL" tag for dax in XFS ruansy.fnst 2021-02-26 19:04 ` Darrick J. Wong 2021-02-26 19:24 ` Dan Williams 2021-02-26 20:51 ` Dave Chinner 2021-02-26 20:59 ` Dan Williams 2021-02-26 21:27 ` Dave Chinner [this message] 2021-02-26 22:41 ` Dan Williams 2021-02-27 22:36 ` Dave Chinner 2021-02-27 23:40 ` Dan Williams 2021-02-28 22:38 ` Dave Chinner 2021-03-01 20:55 ` Dan Williams 2021-03-01 22:46 ` Dave Chinner 2021-03-02 0:32 ` Dan Williams 2021-03-02 2:42 ` Dave Chinner 2021-03-02 3:33 ` Dan Williams 2021-03-02 5:38 ` Dave Chinner 2021-03-02 5:50 ` Dan Williams 2021-03-02 3:28 ` Darrick J. Wong 2021-03-02 5:41 ` Dan Williams 2021-03-02 7:57 ` Dave Chinner 2021-03-02 17:49 ` Dan Williams 2021-03-04 23:40 ` Darrick J. Wong 2021-03-01 7:26 ` Yasunori Goto 2021-03-01 21:34 ` Dan Williams [not found] ` <firstname.lastname@example.org> 2021-03-03 9:29 ` [Ocfs2-devel] [PATCH v2 04/10] fsdax: Introduce dax_iomap_cow_copy() Christoph Hellwig [not found] ` <email@example.com> 2021-03-03 9:31 ` [Ocfs2-devel] [PATCH v2 06/10] fsdax: Add dax_iomap_cow_copy() for dax_iomap_zero Christoph Hellwig [not found] ` <firstname.lastname@example.org> 2021-02-26 4:14 ` [Ocfs2-devel] [PATCH v2 07/10] iomap: Introduce iomap_apply2() for operations on two files Darrick J. Wong 2021-02-26 8:11 ` ruansy.fnst 2021-02-26 8:25 ` Shiyang Ruan 2021-03-04 5:41 ` [Ocfs2-devel] [RESEND PATCH v2.1 " Shiyang Ruan 2021-03-11 12:30 ` Christoph Hellwig 2021-03-09 6:36 ` [Ocfs2-devel] [PATCH v2 00/10] fsdax, xfs: Add reflink&dedupe support for fsdax Xiaoguang Wang 2021-03-10 1:32 ` ruansy.fnst 2021-03-09 16:19 ` Goldwyn Rodrigues 2021-03-10 1:26 ` ruansy.fnst 2021-03-10 12:30 ` Neal Gompa 2021-03-10 13:02 ` Matthew Wilcox 2021-03-10 13:36 ` Neal Gompa 2021-03-10 13:55 ` Matthew Wilcox 2021-03-10 14:21 ` Goldwyn Rodrigues 2021-03-10 14:26 ` Matthew Wilcox 2021-03-10 17:04 ` Goldwyn Rodrigues 2021-03-11 0:53 ` Dan Williams 2021-03-11 8:26 ` Neal Gompa 2021-03-13 13:07 ` Adam Borowski 2021-03-13 16:24 ` Neal Gompa 2021-03-13 22:00 ` Adam Borowski
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