From: Alistair Popple <apopple@nvidia•com>
To: Dave Chinner <david@fromorbit•com>
Cc: linmiaohe@huawei•com, nvdimm@lists•linux.dev, jack@suse•cz,
david@redhat•com, djwong@kernel•org, dave.hansen@linux•intel.com,
peterx@redhat•com, linux-mm@kvack•org, will@kernel•org,
hch@lst•de, dave.jiang@intel•com, vishal.l.verma@intel•com,
linux-doc@vger•kernel.org, willy@infradead•org, jgg@ziepe•ca,
catalin.marinas@arm•com, linux-ext4@vger•kernel.org,
ira.weiny@intel•com, jhubbard@nvidia•com, npiggin@gmail•com,
linux-cxl@vger•kernel.org, bhelgaas@google•com,
dan.j.williams@intel•com, linux-arm-kernel@lists•infradead.org,
tytso@mit•edu, linuxppc-dev@lists•ozlabs.org,
linux-kernel@vger•kernel.org, linux-xfs@vger•kernel.org,
linux-fsdevel@vger•kernel.org, logang@deltatee•com
Subject: Re: [PATCH 00/13] fs/dax: Fix FS DAX page reference counts
Date: Mon, 01 Jul 2024 18:33:34 +1000 [thread overview]
Message-ID: <87plrxo6i5.fsf@nvdebian.thelocal> (raw)
In-Reply-To: <ZoIvhDvzMCw28VBI@dread.disaster.area>
Dave Chinner <david@fromorbit•com> writes:
> On Thu, Jun 27, 2024 at 10:54:15AM +1000, Alistair Popple wrote:
>> FS DAX pages have always maintained their own page reference counts
>> without following the normal rules for page reference counting. In
>> particular pages are considered free when the refcount hits one rather
>> than zero and refcounts are not added when mapping the page.
>>
>> Tracking this requires special PTE bits (PTE_DEVMAP) and a secondary
>> mechanism for allowing GUP to hold references on the page (see
>> get_dev_pagemap). However there doesn't seem to be any reason why FS
>> DAX pages need their own reference counting scheme.
>>
>> By treating the refcounts on these pages the same way as normal pages
>> we can remove a lot of special checks. In particular pXd_trans_huge()
>> becomes the same as pXd_leaf(), although I haven't made that change
>> here. It also frees up a valuable SW define PTE bit on architectures
>> that have devmap PTE bits defined.
>>
>> It also almost certainly allows further clean-up of the devmap managed
>> functions, but I have left that as a future improvment.
>>
>> This is an update to the original RFC rebased onto v6.10-rc5. Unlike
>> the original RFC it passes the same number of ndctl test suite
>> (https://github.com/pmem/ndctl) tests as my current development
>> environment does without these patches.
>
> I strongly suggest running fstests on pmem devices with '-o
> dax=always' mount options to get much more comprehensive fsdax test
> coverage. That exercises a lot of the weird mmap corner cases that
> cause problems so it would be good to actually test that nothing new
> got broken in FSDAX by this patchset.
Thanks Dave, I will do that and report back. I suspect it will turn up
something, given Dan was seeing a crash with these patches.
- Alistair
> -Dave.
prev parent reply other threads:[~2024-07-01 8:35 UTC|newest]
Thread overview: 54+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-06-27 0:54 [PATCH 00/13] fs/dax: Fix FS DAX page reference counts Alistair Popple
2024-06-27 0:54 ` [PATCH 01/13] mm/gup.c: Remove redundant check for PCI P2PDMA page Alistair Popple
2024-06-27 6:36 ` Dan Williams
2024-06-27 0:54 ` [PATCH 02/13] pci/p2pdma: Don't initialise page refcount to one Alistair Popple
2024-06-27 5:30 ` Christoph Hellwig
2024-06-29 21:28 ` Bjorn Helgaas
2024-06-27 0:54 ` [PATCH 03/13] fs/dax: Refactor wait for dax idle page Alistair Popple
2024-06-27 5:31 ` Christoph Hellwig
2024-06-27 0:54 ` [PATCH 04/13] fs/dax: Add dax_page_free callback Alistair Popple
2024-06-27 5:33 ` Christoph Hellwig
2024-06-27 23:48 ` Alistair Popple
2024-06-27 0:54 ` [PATCH 05/13] mm: Allow compound zone device pages Alistair Popple
2024-06-27 5:35 ` Christoph Hellwig
2024-06-27 0:54 ` [PATCH 06/13] mm/memory: Add dax_insert_pfn Alistair Popple
2024-06-27 5:22 ` Christoph Hellwig
2024-06-27 11:33 ` Jan Kara
2024-09-06 6:21 ` Alistair Popple
2024-07-02 7:18 ` David Hildenbrand
2024-07-02 10:47 ` Alistair Popple
2024-07-02 11:46 ` Christoph Hellwig
2024-07-02 11:53 ` David Hildenbrand
2024-06-27 0:54 ` [PATCH 07/13] huge_memory: Allow mappings of PUD sized pages Alistair Popple
2024-06-27 22:26 ` kernel test robot
2024-07-02 7:16 ` David Hildenbrand
2024-07-02 10:19 ` Alistair Popple
2024-07-02 11:02 ` David Hildenbrand
2024-07-02 11:30 ` Alistair Popple
2024-07-02 13:01 ` David Hildenbrand
2024-07-02 11:51 ` Christoph Hellwig
2024-06-27 0:54 ` [PATCH 08/13] huge_memory: Allow mappings of PMD " Alistair Popple
2024-06-27 0:54 ` [PATCH 09/13] gup: Don't allow FOLL_LONGTERM pinning of FS DAX pages Alistair Popple
2024-07-01 8:59 ` David Hildenbrand
2024-07-01 23:47 ` Alistair Popple
2024-07-02 10:48 ` David Hildenbrand
2024-06-27 0:54 ` [PATCH 10/13] fs/dax: Properly refcount fs dax pages Alistair Popple
2024-06-27 5:44 ` Christoph Hellwig
2024-09-06 6:00 ` Alistair Popple
2024-06-27 0:54 ` [PATCH 11/13] huge_memory: Remove dead vmf_insert_pXd code Alistair Popple
2024-07-05 14:24 ` Peter Xu
2024-07-09 4:07 ` Alistair Popple
2024-07-09 15:56 ` Peter Xu
2024-07-12 2:40 ` Alistair Popple
2024-07-12 15:52 ` Peter Xu
2024-06-27 0:54 ` [PATCH 12/13] mm: Remove pXX_devmap callers Alistair Popple
2024-06-27 0:54 ` [PATCH 13/13] mm: Remove devmap related functions and page table bits Alistair Popple
2024-06-27 23:04 ` kernel test robot
2024-06-28 2:12 ` kernel test robot
2024-07-08 11:35 ` Will Deacon
2024-06-27 6:58 ` [PATCH 00/13] fs/dax: Fix FS DAX page reference counts Dan Williams
2024-06-27 7:15 ` Alistair Popple
2024-06-27 20:24 ` Dan Williams
2024-06-28 0:06 ` Alistair Popple
2024-07-01 4:24 ` Dave Chinner
2024-07-01 8:33 ` Alistair Popple [this message]
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