From: Martin Schwidefsky <schwidefsky@de.ibm.com>
To: Christoph Hellwig <hch@lst.de>
Cc: Dan Williams <dan.j.williams@intel.com>,
Andrew Morton <akpm@linux-foundation.org>,
Jan Kara <jack@suse.cz>,
"linux-nvdimm@lists.01.org" <linux-nvdimm@lists.01.org>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Heiko Carstens <heiko.carstens@de.ibm.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>, Paul Mackerras <paulus@samba.org>,
Michael Ellerman <mpe@ellerman.id.au>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
Ross Zwisler <ross.zwisler@linux.intel.com>,
Gerald Schaefer <gerald.schaefer@de.ibm.com>
Subject: Re: [PATCH v3 02/13] dax: require 'struct page' for filesystem dax
Date: Mon, 23 Oct 2017 07:18:35 +0200 [thread overview]
Message-ID: <20171023071835.67ee5210@mschwideX1> (raw)
In-Reply-To: <20171020162933.GA26320@lst.de>
On Fri, 20 Oct 2017 18:29:33 +0200
Christoph Hellwig <hch@lst.de> wrote:
> On Fri, Oct 20, 2017 at 08:23:02AM -0700, Dan Williams wrote:
> > Yes, however it seems these drivers / platforms have been living with
> > the lack of struct page for a long time. So they either don't use DAX,
> > or they have a constrained use case that never triggers
> > get_user_pages(). If it is the latter then they could introduce a new
> > configuration option that bypasses the pfn_t_devmap() check in
> > bdev_dax_supported() and fix up the get_user_pages() paths to fail.
> > So, I'd like to understand how these drivers have been using DAX
> > support without struct page to see if we need a workaround or we can
> > go ahead delete this support. If the usage is limited to
> > execute-in-place perhaps we can do a constrained ->direct_access() for
> > just that case.
>
> For axonram I doubt anyone is using it any more - it was a very for
> the IBM Cell blades, which were produceѕ in a rather limited number.
> And Cell basically seems to be dead as far as I can tell.
>
> For S/390 Martin might be able to help out what the status of xpram
> in general and DAX support in particular is.
The goes back to the time where DAX was called XIP. The initial design
point has been *not* to have struct pages for a large read-only memory
area. There is a block device driver for z/VM that maps a DCSS segment
somewhere in memore (no struct page!) with e.g. the complete /usr
filesystem. The xpram driver is a different beast and has nothing to
do with XIP/DAX.
Now, if any there are very few users of the dcssblk driver out there.
The idea to save a few megabyte for /usr never really took of.
We have to look at our get_user_pages() implementation to see how hard
it would be to make it fail if the target address is for an area without
struct pages.
--
blue skies,
Martin.
"Reality continues to ruin my life." - Calvin.
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next prev parent reply other threads:[~2017-10-23 5:18 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-10-20 2:38 [PATCH v3 00/13] dax: fix dma vs truncate and remove 'page-less' support Dan Williams
2017-10-20 2:39 ` [PATCH v3 01/13] dax: quiet bdev_dax_supported() Dan Williams
2017-10-20 2:39 ` [PATCH v3 02/13] dax: require 'struct page' for filesystem dax Dan Williams
2017-10-20 7:57 ` Christoph Hellwig
2017-10-20 15:23 ` Dan Williams
2017-10-20 16:29 ` Christoph Hellwig
2017-10-20 22:29 ` Dan Williams
2017-10-21 3:20 ` Matthew Wilcox
2017-10-21 4:16 ` Dan Williams
2017-10-21 8:15 ` Christoph Hellwig
2017-10-23 5:18 ` Martin Schwidefsky [this message]
2017-10-23 8:55 ` Dan Williams
2017-10-23 10:44 ` Martin Schwidefsky
2017-10-23 11:20 ` Dan Williams
2017-10-20 2:39 ` [PATCH v3 03/13] dax: stop using VM_MIXEDMAP for dax Dan Williams
2017-10-20 2:39 ` [PATCH v3 04/13] dax: stop using VM_HUGEPAGE " Dan Williams
2017-10-20 2:39 ` [PATCH v3 05/13] dax: stop requiring a live device for dax_flush() Dan Williams
2017-10-20 2:39 ` [PATCH v3 06/13] dax: store pfns in the radix Dan Williams
2017-10-20 2:39 ` [PATCH v3 07/13] dax: warn if dma collides with truncate Dan Williams
2017-10-20 2:39 ` [PATCH v3 08/13] tools/testing/nvdimm: add 'bio_delay' mechanism Dan Williams
2017-10-20 2:39 ` [PATCH v3 09/13] IB/core: disable memory registration of fileystem-dax vmas Dan Williams
2017-10-20 2:39 ` [PATCH v3 10/13] mm: disable get_user_pages_fast() for dax Dan Williams
2017-10-20 2:39 ` [PATCH v3 11/13] fs: use smp_load_acquire in break_{layout,lease} Dan Williams
2017-10-20 12:39 ` Jeffrey Layton
2017-10-20 2:40 ` [PATCH v3 12/13] dax: handle truncate of dma-busy pages Dan Williams
2017-10-20 13:05 ` Jeff Layton
2017-10-20 15:42 ` Dan Williams
2017-10-20 16:32 ` Christoph Hellwig
2017-10-20 17:27 ` Dan Williams
2017-10-20 20:36 ` Brian Foster
2017-10-21 8:11 ` Christoph Hellwig
2017-10-20 2:40 ` [PATCH v3 13/13] xfs: wire up FL_ALLOCATED support Dan Williams
2017-10-20 7:47 ` [PATCH v3 00/13] dax: fix dma vs truncate and remove 'page-less' support Christoph Hellwig
2017-10-20 9:31 ` Christoph Hellwig
2017-10-26 10:58 ` Jan Kara
2017-10-26 23:51 ` Williams, Dan J
2017-10-27 6:48 ` Dave Chinner
2017-10-27 11:42 ` Dan Williams
2017-10-29 21:52 ` Dave Chinner
2017-10-27 6:45 ` Christoph Hellwig
2017-10-29 23:46 ` Dan Williams
2017-10-30 2:00 ` Dave Chinner
2017-10-30 8:38 ` Jan Kara
2017-10-30 11:20 ` Dave Chinner
2017-10-30 17:51 ` Dan Williams
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