From: Jason Gunthorpe <jgg@nvidia.com>
To: Dan Williams <dan.j.williams@intel.com>
Cc: akpm@linux-foundation.org, Jan Kara <jack@suse.cz>,
Christoph Hellwig <hch@lst.de>,
"Darrick J. Wong" <djwong@kernel.org>,
John Hubbard <jhubbard@nvidia.com>,
Matthew Wilcox <willy@infradead.org>,
linux-mm@kvack.org, nvdimm@lists.linux.dev,
linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH 00/13] Fix the DAX-gup mistake
Date: Fri, 9 Sep 2022 08:53:37 -0300 [thread overview]
Message-ID: <YxspQQ7ElQSAN/l3@nvidia.com> (raw)
In-Reply-To: <631a420ad2f28_166f29423@dwillia2-xfh.jf.intel.com.notmuch>
On Thu, Sep 08, 2022 at 12:27:06PM -0700, Dan Williams wrote:
> flag lets the fsdax core track when it has already dropped a page
> reference, but still has use for things like memory-failure to
> opportunistically use page->mapping on a 0-reference page.
This is not straightforward, as discussed before the page->mapping is
allowed to change while the refcount is zero, so there is no generic
way to safely obtain a pointer to the address space from a 0 reference
page.
You'd have to pass the 0 reference page into a new pgmap operation
which could obtain an appropriate internal lock to read page->mapping.
> > I'm not sure what it has to do with normal_page?
>
> This thread is mainly about DAX slowly reinventing _mapcount that gets
> managed in all the right places for a normal_page. Longer term I think
> we either need to get back to the page-less DAX experiment and find a
> way to unwind some of this page usage creep, or cut over to finally
> making DAX-pages be normal pages and delete most of the special case
> handling in fs/dax.c. I am open to discussing the former, but I think
> the latter is more likely.
I think the latter is inevitable at this point..
Jason
next prev parent reply other threads:[~2022-09-09 11:53 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-04 2:16 [PATCH 00/13] Fix the DAX-gup mistake Dan Williams
2022-09-04 2:16 ` [PATCH 01/13] fsdax: Rename "busy page" to "pinned page" Dan Williams
2022-09-04 2:16 ` [PATCH 02/13] fsdax: Use page_maybe_dma_pinned() for DAX vs DMA collisions Dan Williams
2022-09-06 12:07 ` Jason Gunthorpe
2022-09-04 2:16 ` [PATCH 03/13] fsdax: Delete put_devmap_managed_page_refs() Dan Williams
2022-09-04 2:16 ` [PATCH 04/13] fsdax: Update dax_insert_entry() calling convention to return an error Dan Williams
2022-09-04 2:16 ` [PATCH 05/13] fsdax: Cleanup dax_associate_entry() Dan Williams
2022-09-04 2:16 ` [PATCH 06/13] fsdax: Rework dax_insert_entry() calling convention Dan Williams
2022-09-04 2:16 ` [PATCH 07/13] fsdax: Manage pgmap references at entry insertion and deletion Dan Williams
2022-09-06 12:30 ` Jason Gunthorpe
2022-09-04 2:16 ` [PATCH 08/13] devdax: Minor warning fixups Dan Williams
2022-09-04 2:16 ` [PATCH 09/13] devdax: Move address_space helpers to the DAX core Dan Williams
2022-09-04 5:53 ` kernel test robot
2022-09-04 2:16 ` [PATCH 10/13] dax: Prep dax_{associate, disassociate}_entry() for compound pages Dan Williams
2022-09-04 2:17 ` [PATCH 11/13] devdax: add PUD support to the DAX mapping infrastructure Dan Williams
2022-09-04 2:17 ` [PATCH 12/13] devdax: Use dax_insert_entry() + dax_delete_mapping_entry() Dan Williams
2022-09-04 2:17 ` [PATCH 13/13] mm/gup: Drop DAX pgmap accounting Dan Williams
2022-09-06 13:05 ` [PATCH 00/13] Fix the DAX-gup mistake Jason Gunthorpe
2022-09-06 17:23 ` Dan Williams
2022-09-06 17:29 ` Jason Gunthorpe
2022-09-06 18:37 ` Dan Williams
2022-09-06 18:49 ` Jason Gunthorpe
2022-09-06 19:41 ` Dan Williams
2022-09-07 0:54 ` Dan Williams
2022-09-07 12:58 ` Jason Gunthorpe
2022-09-07 17:10 ` Dan Williams
2022-09-07 18:43 ` Dan Williams
2022-09-07 19:30 ` Jason Gunthorpe
2022-09-07 20:45 ` Dan Williams
2022-09-08 18:49 ` Jason Gunthorpe
2022-09-08 19:27 ` Dan Williams
2022-09-09 11:53 ` Jason Gunthorpe [this message]
2022-09-09 17:52 ` Dan Williams
2022-09-09 18:11 ` Matthew Wilcox
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