From: Dan Williams <dan.j.williams@intel.com>
To: Jan Kara <jack@suse.cz>, Alistair Popple <apopple@nvidia.com>
Cc: <linux-mm@kvack.org>, <david@fromorbit.com>,
<dan.j.williams@intel.com>, <jhubbard@nvidia.com>,
<rcampbell@nvidia.com>, <willy@infradead.org>, <jgg@nvidia.com>,
<linux-fsdevel@vger.kernel.org>, <jack@suse.cz>,
<djwong@kernel.org>, <hch@lst.de>, <david@redhat.com>,
<ruansy.fnst@fujitsu.com>, <nvdimm@lists.linux.dev>,
<linux-xfs@vger.kernel.org>, <linux-ext4@vger.kernel.org>,
<jglisse@redhat.com>
Subject: Re: [RFC 04/10] fs/dax: Don't track page mapping/index
Date: Fri, 12 Apr 2024 10:31:52 -0700 [thread overview]
Message-ID: <66197008db9fc_36222e294b8@dwillia2-xfh.jf.intel.com.notmuch> (raw)
In-Reply-To: <20240412152208.m25mjo3xjfyawcaj@quack3>
Jan Kara wrote:
> On Thu 11-04-24 10:57:25, Alistair Popple wrote:
> > The page->mapping and page->index fields are normally used by the
> > pagecache and rmap for looking up virtual mappings of pages. FS DAX
> > implements it's own kind of page cache and rmap look ups so these
> > fields are unnecessary. They are currently only used to detect
> > error/warning conditions which should never occur.
> >
> > A future change will change the way shared mappings are detected by
> > doing normal page reference counting instead, so remove the
> > unnecessary checks.
> >
> > Signed-off-by: Alistair Popple <apopple@nvidia.com>
> ...
> > -/*
> > - * When it is called in dax_insert_entry(), the shared flag will indicate that
> > - * whether this entry is shared by multiple files. If so, set the page->mapping
> > - * PAGE_MAPPING_DAX_SHARED, and use page->share as refcount.
> > - */
> > -static void dax_associate_entry(void *entry, struct address_space *mapping,
> > - struct vm_area_struct *vma, unsigned long address, bool shared)
> > -{
> > - unsigned long size = dax_entry_size(entry), pfn, index;
> > - int i = 0;
> > -
> > - if (IS_ENABLED(CONFIG_FS_DAX_LIMITED))
> > - return;
> > -
> > - index = linear_page_index(vma, address & ~(size - 1));
> > - for_each_mapped_pfn(entry, pfn) {
> > - struct page *page = pfn_to_page(pfn);
> > -
> > - if (shared) {
> > - dax_page_share_get(page);
> > - } else {
> > - WARN_ON_ONCE(page->mapping);
> > - page->mapping = mapping;
> > - page->index = index + i++;
> > - }
> > - }
> > -}
>
> Hum, but what about existing uses of folio->mapping and folio->index in
> fs/dax.c? AFAICT this patch breaks them. What am I missing? How can this
> ever work?
Right, as far as I can see every fsdax filesystem would need to be
converted to use dax_holder_operations() so that the fs can backfill
->mapping and ->index.
next prev parent reply other threads:[~2024-04-12 17:31 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-11 0:57 [RFC 00/10] fs/dax: Fix FS DAX page reference counts Alistair Popple
2024-04-11 0:57 ` [RFC 01/10] mm/gup.c: Remove redundant check for PCI P2PDMA page Alistair Popple
2024-04-11 12:59 ` Jason Gunthorpe
2024-04-11 13:47 ` David Hildenbrand
2024-04-12 1:37 ` Alistair Popple
2024-04-11 0:57 ` [RFC 02/10] mm/hmm: Remove dead check for HugeTLB and FS DAX Alistair Popple
2024-04-11 12:25 ` Jason Gunthorpe
2024-04-11 13:37 ` Peter Xu
2024-04-12 1:28 ` Alistair Popple
2024-04-11 0:57 ` [RFC 03/10] pci/p2pdma: Don't initialise page refcount to one Alistair Popple
2024-04-11 12:29 ` Jason Gunthorpe
2024-04-12 5:40 ` Alistair Popple
2024-04-12 17:20 ` Dan Williams
2024-05-09 21:59 ` Logan Gunthorpe
2024-05-09 23:14 ` Alistair Popple
2024-04-11 0:57 ` [RFC 04/10] fs/dax: Don't track page mapping/index Alistair Popple
2024-04-12 15:22 ` Jan Kara
2024-04-12 17:31 ` Dan Williams [this message]
2024-04-15 7:03 ` Alistair Popple
2024-04-15 20:51 ` Dan Williams
2024-04-16 0:07 ` Alistair Popple
2024-04-16 0:36 ` Dan Williams
2024-04-12 17:21 ` Dan Williams
2024-04-11 0:57 ` [RFC 05/10] fs/dax: Refactor wait for dax idle page Alistair Popple
2024-04-12 14:37 ` Jan Kara
2024-04-13 20:19 ` John Hubbard
2024-04-15 8:41 ` Alistair Popple
2024-04-11 0:57 ` [RFC 06/10] fs/dax: Add dax_page_free callback Alistair Popple
2024-04-11 0:57 ` [RFC 07/10] mm: Allow compound zone device pages Alistair Popple
2024-04-11 12:32 ` Jason Gunthorpe
2024-04-11 14:10 ` Matthew Wilcox
2024-04-12 1:38 ` Alistair Popple
2024-04-11 0:57 ` [RFC 08/10] fs/dax: Properly refcount fs dax pages Alistair Popple
2024-04-11 0:57 ` [RFC 09/10] mm/khugepage.c: Warn if trying to scan devmap pmd Alistair Popple
2024-04-11 13:45 ` David Hildenbrand
2024-04-12 1:34 ` Alistair Popple
2024-04-11 0:57 ` [RFC 10/10] mm: Remove pXX_devmap Alistair Popple
2024-04-11 12:57 ` Jason Gunthorpe
2024-04-11 17:28 ` [RFC 00/10] fs/dax: Fix FS DAX page reference counts Dan Williams
2024-04-11 17:35 ` Jason Gunthorpe
2024-04-11 17:56 ` Dan Williams
2024-04-12 3:54 ` Alistair Popple
2024-04-12 6:55 ` Alistair Popple
2024-04-12 11:53 ` Jason Gunthorpe
2024-04-12 17:32 ` Dan Williams
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