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From: Alistair Popple <apopple@nvidia.com>
To: Dan Williams <dan.j.williams@intel.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>,
	akpm@linux-foundation.org, Matthew Wilcox <willy@infradead.org>,
	Jan Kara <jack@suse.cz>, "Darrick J. Wong" <djwong@kernel.org>,
	Christoph Hellwig <hch@lst.de>,
	John Hubbard <jhubbard@nvidia.com>,
	linux-fsdevel@vger.kernel.org, nvdimm@lists.linux.dev,
	linux-xfs@vger.kernel.org, linux-mm@kvack.org,
	linux-ext4@vger.kernel.org
Subject: Re: [PATCH v2 16/18] mm/memremap_pages: Support initializing pages to a zero reference count
Date: Mon, 26 Sep 2022 16:17:18 +1000	[thread overview]
Message-ID: <87wn9qlklh.fsf@nvdebian.thelocal> (raw)
In-Reply-To: <632bc9acdbad1_349629435@dwillia2-xfh.jf.intel.com.notmuch>


Dan Williams <dan.j.williams@intel.com> writes:

[...]

>> >> > > How on earth can a free'd page have both a 0 and 1 refcount??
>> >> >
>> >> > This is residual wonkiness from memremap_pages() handing out pages with
>> >> > elevated reference counts at the outset.
>> >>
>> >> I think the answer to my question is the above troubled code where we
>> >> still set the page refcount back to 1 even in the page_free path, so
>> >> there is some consistency "a freed paged may have a refcount of 1" for
>> >> the driver.
>> >>
>> >> So, I guess this patch makes sense but I would put more noise around
>> >> INIT_PAGEMAP_BUSY (eg annotate every driver that is using it with the
>> >> explicit constant) and alert people that they need to fix their stuff
>> >> to get rid of it.
>> >
>> > Sounds reasonable.
>> >
>> >> We should definately try to fix hmm_test as well so people have a good
>> >> reference code to follow in fixing the other drivers :(
>> >
>> > Oh, that's a good idea. I can probably fix that up and leave it to the
>> > GPU driver folks to catch up with that example so we can kill off
>> > INIT_PAGEMAP_BUSY.
>>
>> I'm hoping to send my series that fixes up all drivers using device
>> coherent/private later this week or early next. So you could also just
>> wait for that and remove INIT_PAGEMAP_BUSY entirely.
>
> Oh, perfect, thanks!

See
https://lore.kernel.org/linux-mm/3d74bb439723c7e46cbe47d1711795308aee4ae3.1664171943.git-series.apopple@nvidia.com/

I already had this in a series because the change was motivated by a
later patch there, but it's a standalone change and there's no reason it
couldn't be split out into it's own patch if that's better for you.

 - Alistair

  reply	other threads:[~2022-09-26  6:24 UTC|newest]

Thread overview: 84+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-09-16  3:35 [PATCH v2 00/18] Fix the DAX-gup mistake Dan Williams
2022-09-16  3:35 ` [PATCH v2 01/18] fsdax: Wait on @page not @page->_refcount Dan Williams
2022-09-20 14:30   ` Jason Gunthorpe
2022-09-16  3:35 ` [PATCH v2 02/18] fsdax: Use dax_page_idle() to document DAX busy page checking Dan Williams
2022-09-20 14:31   ` Jason Gunthorpe
2022-09-16  3:35 ` [PATCH v2 03/18] fsdax: Include unmapped inodes for page-idle detection Dan Williams
2022-09-16  3:35 ` [PATCH v2 04/18] ext4: Add ext4_break_layouts() to the inode eviction path Dan Williams
2022-09-16  3:35 ` [PATCH v2 05/18] xfs: Add xfs_break_layouts() " Dan Williams
2022-09-18 22:57   ` Dave Chinner
2022-09-19 16:11     ` Dan Williams
2022-09-19 21:29       ` Dave Chinner
2022-09-20 16:44         ` Dan Williams
2022-09-21 22:14           ` Dave Chinner
2022-09-21 22:28             ` Jason Gunthorpe
2022-09-23  0:18               ` Dave Chinner
2022-09-23  0:41                 ` Dan Williams
2022-09-23  2:10                   ` Dave Chinner
2022-09-23  9:38                     ` Jan Kara
2022-09-23 23:06                       ` Dan Williams
2022-09-25 23:54                       ` Dave Chinner
2022-09-26 14:10                         ` Jan Kara
2022-09-29 23:33                           ` Dan Williams
2022-09-30 13:41                             ` Jan Kara
2022-09-30 17:56                               ` Dan Williams
2022-09-30 18:06                                 ` Jason Gunthorpe
2022-09-30 18:46                                   ` Dan Williams
2022-10-03  7:55                                   ` Jan Kara
2022-09-23 12:39                     ` Jason Gunthorpe
2022-09-26  0:34                       ` Dave Chinner
2022-09-26 13:04                         ` Jason Gunthorpe
2022-09-22  0:02             ` Dan Williams
2022-09-22  0:10               ` Jason Gunthorpe
2022-09-16  3:35 ` [PATCH v2 06/18] fsdax: Rework dax_layout_busy_page() to dax_zap_mappings() Dan Williams
2022-09-16  3:35 ` [PATCH v2 07/18] fsdax: Update dax_insert_entry() calling convention to return an error Dan Williams
2022-09-16  3:35 ` [PATCH v2 08/18] fsdax: Cleanup dax_associate_entry() Dan Williams
2022-09-16  3:36 ` [PATCH v2 09/18] fsdax: Rework dax_insert_entry() calling convention Dan Williams
2022-09-16  3:36 ` [PATCH v2 10/18] fsdax: Manage pgmap references at entry insertion and deletion Dan Williams
2022-09-21 14:03   ` Jason Gunthorpe
2022-09-21 15:18     ` Dan Williams
2022-09-21 21:38       ` Dan Williams
2022-09-21 22:07         ` Jason Gunthorpe
2022-09-22  0:14           ` Dan Williams
2022-09-22  0:25             ` Jason Gunthorpe
2022-09-22  2:17               ` Dan Williams
2022-09-22 17:55                 ` Jason Gunthorpe
2022-09-22 21:54                   ` Dan Williams
2022-09-23  1:36                     ` Dave Chinner
2022-09-23  2:01                       ` Dan Williams
2022-09-23 13:24                     ` Jason Gunthorpe
2022-09-23 16:29                       ` Dan Williams
2022-09-23 17:42                         ` Jason Gunthorpe
2022-09-23 19:03                           ` Dan Williams
2022-09-23 19:23                             ` Jason Gunthorpe
2022-09-27  6:07                             ` Alistair Popple
2022-09-27 12:56                               ` Jason Gunthorpe
2022-09-16  3:36 ` [PATCH v2 11/18] devdax: Minor warning fixups Dan Williams
2022-09-16  3:36 ` [PATCH v2 12/18] devdax: Move address_space helpers to the DAX core Dan Williams
2022-09-27  6:20   ` Alistair Popple
2022-09-29 22:38     ` Dan Williams
2022-09-16  3:36 ` [PATCH v2 13/18] dax: Prep mapping helpers for compound pages Dan Williams
2022-09-21 14:06   ` Jason Gunthorpe
2022-09-21 15:19     ` Dan Williams
2022-09-16  3:36 ` [PATCH v2 14/18] devdax: add PUD support to the DAX mapping infrastructure Dan Williams
2022-09-16  3:36 ` [PATCH v2 15/18] devdax: Use dax_insert_entry() + dax_delete_mapping_entry() Dan Williams
2022-09-21 14:10   ` Jason Gunthorpe
2022-09-21 15:48     ` Dan Williams
2022-09-21 22:23       ` Jason Gunthorpe
2022-09-22  0:15         ` Dan Williams
2022-09-16  3:36 ` [PATCH v2 16/18] mm/memremap_pages: Support initializing pages to a zero reference count Dan Williams
2022-09-21 15:24   ` Jason Gunthorpe
2022-09-21 23:45     ` Dan Williams
2022-09-22  0:03       ` Alistair Popple
2022-09-22  0:04       ` Jason Gunthorpe
2022-09-22  0:34         ` Dan Williams
2022-09-22  1:36           ` Alistair Popple
2022-09-22  2:34             ` Dan Williams
2022-09-26  6:17               ` Alistair Popple [this message]
2022-09-22  0:13       ` John Hubbard
2022-09-16  3:36 ` [PATCH v2 17/18] fsdax: Delete put_devmap_managed_page_refs() Dan Williams
2022-09-16  3:36 ` [PATCH v2 18/18] mm/gup: Drop DAX pgmap accounting Dan Williams
2022-09-20 14:29 ` [PATCH v2 00/18] Fix the DAX-gup mistake Jason Gunthorpe
2022-09-20 16:50   ` Dan Williams
2022-11-09  0:20 ` Andrew Morton
2022-11-09 11:38   ` Jan Kara

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