From: Gerald Schaefer <email@example.com> To: Dan Williams <firstname.lastname@example.org> Cc: "Christoph Hellwig" <email@example.com>, "Jan Kara" <firstname.lastname@example.org>, linux-nvdimm <email@example.com>, "Martin Schwidefsky" <firstname.lastname@example.org>, "Heiko Carstens" <email@example.com>, "Michal Hocko" <firstname.lastname@example.org>, "kbuild test robot" <email@example.com>, "Thomas Meyer" <firstname.lastname@example.org>, "Dave Jiang" <email@example.com>, "Jérôme Glisse" <firstname.lastname@example.org>, linux-fsdevel <email@example.com>, "Linux MM" <firstname.lastname@example.org> Subject: Re: [PATCH v10] mm: introduce MEMORY_DEVICE_FS_DAX and CONFIG_DEV_PAGEMAP_OPS Date: Fri, 1 Jun 2018 17:01:00 +0200 [thread overview] Message-ID: <20180601170100.0a8e5567@thinkpad> (raw) In-Reply-To: <CAPcyv4gRvG=yT==SPgF940F7v9FqGqG-dQ8Vjcm0LPch86i1RA@mail.gmail.com> On Tue, 29 May 2018 13:26:33 -0700 Dan Williams <email@example.com> wrote: > On Wed, May 23, 2018 at 11:50 AM, Gerald Schaefer > <firstname.lastname@example.org> wrote: > > On Tue, 22 May 2018 08:28:06 +0200 > > Christoph Hellwig <email@example.com> wrote: > > > >> On Mon, May 21, 2018 at 11:04:10AM +0200, Jan Kara wrote: > >> > We definitely do have customers using "execute in place" on s390x from > >> > dcssblk. I've got about two bug reports for it when customers were updating > >> > from old kernels using original XIP to kernels using DAX. So we need to > >> > keep that working. > >> > >> That is all good an fine, but I think time has come where s390 needs > >> to migrate to provide the pmem API so that we can get rid of these > >> special cases. Especially given that the old XIP/legacy DAX has all > >> kinds of known bugs at this point in time. > > > > I haven't yet looked at this patch series, but I can feel that this > > FS_DAX_LIMITED workaround is beginning to cause some headaches, apart > > from being quite ugly of course. > > > > Just to make sure I still understand the basic problem, which I thought > > was missing struct pages for the dcssblk memory, what exactly do you > > mean with "provide the pmem API", is there more to do? > > No, just 'struct page' is needed. > > What used to be the pmem API is now pushed down into to dax_operations > provided by the device driver. dcssblk is free to just redirect to the > generic implementations for copy_from_iter() and copy_to_iter(), and > be done. I.e. we've removed the "pmem API" requirement. > > > I do have a prototype patch lying around that adds struct pages, but > > didn't yet have time to fully test/complete it. Of course we initially > > introduced XIP as a mechanism to reduce memory consumption, and that > > is probably the use case for the remaining customer(s). Adding struct > > pages would somehow reduce that benefit, but as long as we can still > > "execute in place", I guess it will be OK. > > The pmem driver has the option to allocate the 'struct page' map out > of pmem directly. If the overhead of having the map in System RAM is > too high it could borrow the same approach, but that adds another > degree of configuration complexity freedom. > Thanks for clarifying, and mentioning the pmem altmap support, that looks interesting. I also noticed that I probably should enable CONFIG_ZONE_DEVICE for s390, and use devm_memremap_pages() to get the struct pages, rather than my homegrown solution so far. This will take some time however, so I hope you can live with the FS_DAX_LIMITED a little longer. Regards, Gerald
next prev parent reply other threads:[~2018-06-01 15:01 UTC|newest] Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top 2018-05-17 20:06 Dan Williams 2018-05-18 9:00 ` Jan Kara 2018-05-18 9:46 ` Christoph Hellwig 2018-05-18 16:00 ` Dan Williams 2018-05-21 9:04 ` Jan Kara 2018-05-22 6:28 ` Christoph Hellwig 2018-05-23 18:50 ` Gerald Schaefer 2018-05-29 20:26 ` Dan Williams 2018-06-01 15:01 ` Gerald Schaefer [this message] 2018-06-02 0:03 ` Dan Williams
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