* Re: [PATCH] ext4/xfs: add page refcount helper
2020-10-06 23:09 [PATCH] ext4/xfs: add page refcount helper Ralph Campbell
@ 2020-10-07 2:40 ` Dan Williams
2020-10-07 14:41 ` Theodore Y. Ts'o
2020-10-07 8:25 ` Jan Kara
2020-10-07 15:36 ` Darrick J. Wong
2 siblings, 1 reply; 7+ messages in thread
From: Dan Williams @ 2020-10-07 2:40 UTC (permalink / raw)
To: Ralph Campbell
Cc: Linux MM, linux-xfs, linux-fsdevel, linux-nvdimm,
Linux Kernel Mailing List, linux-ext4, Matthew Wilcox, Jan Kara,
Alexander Viro, Theodore Ts'o, Christoph Hellwig,
Andreas Dilger, Darrick J. Wong, Andrew Morton
On Tue, Oct 6, 2020 at 4:09 PM Ralph Campbell <rcampbell@nvidia.com> wrote:
>
> There are several places where ZONE_DEVICE struct pages assume a reference
> count == 1 means the page is idle and free. Instead of open coding this,
> add a helper function to hide this detail.
>
> Signed-off-by: Ralph Campbell <rcampbell@nvidia.com>
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> ---
>
> I'm resending this as a separate patch since I think it is ready to
> merge. Originally, this was part of an RFC and is unchanged from v3:
> https://lore.kernel.org/linux-mm/20201001181715.17416-1-rcampbell@nvidia.com
>
> It applies cleanly to linux-5.9.0-rc7-mm1 but doesn't really
> depend on anything, just simple merge conflicts when applied to
> other trees.
> I'll let the various maintainers decide which tree and when to merge.
> It isn't urgent since it is a clean up patch.
Thanks Ralph, it looks good to me. Jan, or Ted care to ack? I don't
have much else pending for dax at the moment as Andrew is carrying my
dax updates for this cycle. Andrew please take this into -mm if you
get a chance. Otherwise I'll cycle back to it when some other dax
updates arrive in my queue.
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] ext4/xfs: add page refcount helper
2020-10-07 2:40 ` Dan Williams
@ 2020-10-07 14:41 ` Theodore Y. Ts'o
0 siblings, 0 replies; 7+ messages in thread
From: Theodore Y. Ts'o @ 2020-10-07 14:41 UTC (permalink / raw)
To: Dan Williams
Cc: Ralph Campbell, Linux MM, linux-xfs, linux-fsdevel, linux-nvdimm,
Linux Kernel Mailing List, linux-ext4, Matthew Wilcox, Jan Kara,
Alexander Viro, Christoph Hellwig, Andreas Dilger,
Darrick J. Wong, Andrew Morton
On Tue, Oct 06, 2020 at 07:40:05PM -0700, Dan Williams wrote:
> On Tue, Oct 6, 2020 at 4:09 PM Ralph Campbell <rcampbell@nvidia.com> wrote:
> >
> > There are several places where ZONE_DEVICE struct pages assume a reference
> > count == 1 means the page is idle and free. Instead of open coding this,
> > add a helper function to hide this detail.
> >
> > Signed-off-by: Ralph Campbell <rcampbell@nvidia.com>
> > Reviewed-by: Christoph Hellwig <hch@lst.de>
> > ---
> >
> > I'm resending this as a separate patch since I think it is ready to
> > merge. Originally, this was part of an RFC and is unchanged from v3:
> > https://lore.kernel.org/linux-mm/20201001181715.17416-1-rcampbell@nvidia.com
> >
> > It applies cleanly to linux-5.9.0-rc7-mm1 but doesn't really
> > depend on anything, just simple merge conflicts when applied to
> > other trees.
> > I'll let the various maintainers decide which tree and when to merge.
> > It isn't urgent since it is a clean up patch.
>
> Thanks Ralph, it looks good to me. Jan, or Ted care to ack? I don't
> have much else pending for dax at the moment as Andrew is carrying my
> dax updates for this cycle. Andrew please take this into -mm if you
> get a chance. Otherwise I'll cycle back to it when some other dax
> updates arrive in my queue.
Acked-by: Theodore Ts'o <tytso@mit.edu> # for fs/ext4/inode.c
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] ext4/xfs: add page refcount helper
2020-10-06 23:09 [PATCH] ext4/xfs: add page refcount helper Ralph Campbell
2020-10-07 2:40 ` Dan Williams
@ 2020-10-07 8:25 ` Jan Kara
2020-10-07 18:12 ` Ralph Campbell
2020-10-07 21:59 ` Dan Williams
2020-10-07 15:36 ` Darrick J. Wong
2 siblings, 2 replies; 7+ messages in thread
From: Jan Kara @ 2020-10-07 8:25 UTC (permalink / raw)
To: Ralph Campbell
Cc: linux-mm, linux-xfs, linux-fsdevel, linux-nvdimm, linux-kernel,
linux-ext4, Dan Williams, Matthew Wilcox, Jan Kara,
Alexander Viro, Theodore Ts'o, Christoph Hellwig,
Andreas Dilger, Darrick J. Wong, Andrew Morton
On Tue 06-10-20 16:09:30, Ralph Campbell wrote:
> There are several places where ZONE_DEVICE struct pages assume a reference
> count == 1 means the page is idle and free. Instead of open coding this,
> add a helper function to hide this detail.
>
> Signed-off-by: Ralph Campbell <rcampbell@nvidia.com>
> Reviewed-by: Christoph Hellwig <hch@lst.de>
Looks as sane direction but if we are going to abstract checks when
ZONE_DEVICE page is idle, we should also update e.g.
mm/swap.c:put_devmap_managed_page() or
mm/gup.c:__unpin_devmap_managed_user_page() (there may be more places like
this but I found at least these two...). Maybe Dan has more thoughts about
this.
Honza
> diff --git a/fs/dax.c b/fs/dax.c
> index 5b47834f2e1b..85c63f735909 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -358,7 +358,7 @@ static void dax_disassociate_entry(void *entry, struct address_space *mapping,
> for_each_mapped_pfn(entry, pfn) {
> struct page *page = pfn_to_page(pfn);
>
> - WARN_ON_ONCE(trunc && page_ref_count(page) > 1);
> + WARN_ON_ONCE(trunc && !dax_layout_is_idle_page(page));
> WARN_ON_ONCE(page->mapping && page->mapping != mapping);
> page->mapping = NULL;
> page->index = 0;
> @@ -372,7 +372,7 @@ static struct page *dax_busy_page(void *entry)
> for_each_mapped_pfn(entry, pfn) {
> struct page *page = pfn_to_page(pfn);
>
> - if (page_ref_count(page) > 1)
> + if (!dax_layout_is_idle_page(page))
> return page;
> }
> return NULL;
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 771ed8b1fadb..132620cbfa13 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -3937,10 +3937,7 @@ int ext4_break_layouts(struct inode *inode)
> if (!page)
> return 0;
>
> - error = ___wait_var_event(&page->_refcount,
> - atomic_read(&page->_refcount) == 1,
> - TASK_INTERRUPTIBLE, 0, 0,
> - ext4_wait_dax_page(ei));
> + error = dax_wait_page(ei, page, ext4_wait_dax_page);
> } while (error == 0);
>
> return error;
> diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
> index 3d1b95124744..a5304aaeaa3a 100644
> --- a/fs/xfs/xfs_file.c
> +++ b/fs/xfs/xfs_file.c
> @@ -749,9 +749,7 @@ xfs_break_dax_layouts(
> return 0;
>
> *retry = true;
> - return ___wait_var_event(&page->_refcount,
> - atomic_read(&page->_refcount) == 1, TASK_INTERRUPTIBLE,
> - 0, 0, xfs_wait_dax_page(inode));
> + return dax_wait_page(inode, page, xfs_wait_dax_page);
> }
>
> int
> diff --git a/include/linux/dax.h b/include/linux/dax.h
> index b52f084aa643..8909a91cd381 100644
> --- a/include/linux/dax.h
> +++ b/include/linux/dax.h
> @@ -243,6 +243,16 @@ static inline bool dax_mapping(struct address_space *mapping)
> return mapping->host && IS_DAX(mapping->host);
> }
>
> +static inline bool dax_layout_is_idle_page(struct page *page)
> +{
> + return page_ref_count(page) == 1;
> +}
> +
> +#define dax_wait_page(_inode, _page, _wait_cb) \
> + ___wait_var_event(&(_page)->_refcount, \
> + dax_layout_is_idle_page(_page), \
> + TASK_INTERRUPTIBLE, 0, 0, _wait_cb(_inode))
> +
> #ifdef CONFIG_DEV_DAX_HMEM_DEVICES
> void hmem_register_device(int target_nid, struct resource *r);
> #else
> --
> 2.20.1
>
--
Jan Kara <jack@suse.com>
SUSE Labs, CR
^ permalink raw reply [flat|nested] 7+ messages in thread* Re: [PATCH] ext4/xfs: add page refcount helper
2020-10-07 8:25 ` Jan Kara
@ 2020-10-07 18:12 ` Ralph Campbell
2020-10-07 21:59 ` Dan Williams
1 sibling, 0 replies; 7+ messages in thread
From: Ralph Campbell @ 2020-10-07 18:12 UTC (permalink / raw)
To: Jan Kara
Cc: linux-mm, linux-xfs, linux-fsdevel, linux-nvdimm, linux-kernel,
linux-ext4, Dan Williams, Matthew Wilcox, Alexander Viro,
Theodore Ts'o, Christoph Hellwig, Andreas Dilger,
Darrick J. Wong, Andrew Morton
On 10/7/20 1:25 AM, Jan Kara wrote:
> On Tue 06-10-20 16:09:30, Ralph Campbell wrote:
>> There are several places where ZONE_DEVICE struct pages assume a reference
>> count == 1 means the page is idle and free. Instead of open coding this,
>> add a helper function to hide this detail.
>>
>> Signed-off-by: Ralph Campbell <rcampbell@nvidia.com>
>> Reviewed-by: Christoph Hellwig <hch@lst.de>
>
> Looks as sane direction but if we are going to abstract checks when
> ZONE_DEVICE page is idle, we should also update e.g.
> mm/swap.c:put_devmap_managed_page() or
> mm/gup.c:__unpin_devmap_managed_user_page() (there may be more places like
> this but I found at least these two...). Maybe Dan has more thoughts about
> this.
>
> Honza
I think this is a good point but I would like to make that a follow on
patch rather than add to this one.
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] ext4/xfs: add page refcount helper
2020-10-07 8:25 ` Jan Kara
2020-10-07 18:12 ` Ralph Campbell
@ 2020-10-07 21:59 ` Dan Williams
1 sibling, 0 replies; 7+ messages in thread
From: Dan Williams @ 2020-10-07 21:59 UTC (permalink / raw)
To: Jan Kara
Cc: Ralph Campbell, Linux MM, linux-xfs, linux-fsdevel, linux-nvdimm,
Linux Kernel Mailing List, linux-ext4, Matthew Wilcox,
Alexander Viro, Theodore Ts'o, Christoph Hellwig,
Andreas Dilger, Darrick J. Wong, Andrew Morton
On Wed, Oct 7, 2020 at 1:25 AM Jan Kara <jack@suse.cz> wrote:
>
> On Tue 06-10-20 16:09:30, Ralph Campbell wrote:
> > There are several places where ZONE_DEVICE struct pages assume a reference
> > count == 1 means the page is idle and free. Instead of open coding this,
> > add a helper function to hide this detail.
> >
> > Signed-off-by: Ralph Campbell <rcampbell@nvidia.com>
> > Reviewed-by: Christoph Hellwig <hch@lst.de>
>
> Looks as sane direction but if we are going to abstract checks when
> ZONE_DEVICE page is idle, we should also update e.g.
> mm/swap.c:put_devmap_managed_page() or
> mm/gup.c:__unpin_devmap_managed_user_page() (there may be more places like
> this but I found at least these two...). Maybe Dan has more thoughts about
> this.
Yes, but I think that cleanup comes once the idle page count is
unified to be 0 across typical and ZONE_DEVICE pages. Then
free_devmap_managed_page() can be moved internal to __put_page(). For
this patch it's just hiding the "idle == 1" assumption from
dax-filesystems.
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] ext4/xfs: add page refcount helper
2020-10-06 23:09 [PATCH] ext4/xfs: add page refcount helper Ralph Campbell
2020-10-07 2:40 ` Dan Williams
2020-10-07 8:25 ` Jan Kara
@ 2020-10-07 15:36 ` Darrick J. Wong
2 siblings, 0 replies; 7+ messages in thread
From: Darrick J. Wong @ 2020-10-07 15:36 UTC (permalink / raw)
To: Ralph Campbell
Cc: linux-mm, linux-xfs, linux-fsdevel, linux-nvdimm, linux-kernel,
linux-ext4, Dan Williams, Matthew Wilcox, Jan Kara,
Alexander Viro, Theodore Ts'o, Christoph Hellwig,
Andreas Dilger, Andrew Morton
On Tue, Oct 06, 2020 at 04:09:30PM -0700, Ralph Campbell wrote:
> There are several places where ZONE_DEVICE struct pages assume a reference
> count == 1 means the page is idle and free. Instead of open coding this,
> add a helper function to hide this detail.
>
> Signed-off-by: Ralph Campbell <rcampbell@nvidia.com>
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> ---
>
> I'm resending this as a separate patch since I think it is ready to
> merge. Originally, this was part of an RFC and is unchanged from v3:
> https://lore.kernel.org/linux-mm/20201001181715.17416-1-rcampbell@nvidia.com
>
> It applies cleanly to linux-5.9.0-rc7-mm1 but doesn't really
> depend on anything, just simple merge conflicts when applied to
> other trees.
> I'll let the various maintainers decide which tree and when to merge.
> It isn't urgent since it is a clean up patch.
>
> fs/dax.c | 4 ++--
> fs/ext4/inode.c | 5 +----
> fs/xfs/xfs_file.c | 4 +---
> include/linux/dax.h | 10 ++++++++++
> 4 files changed, 14 insertions(+), 9 deletions(-)
>
> diff --git a/fs/dax.c b/fs/dax.c
> index 5b47834f2e1b..85c63f735909 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -358,7 +358,7 @@ static void dax_disassociate_entry(void *entry, struct address_space *mapping,
> for_each_mapped_pfn(entry, pfn) {
> struct page *page = pfn_to_page(pfn);
>
> - WARN_ON_ONCE(trunc && page_ref_count(page) > 1);
> + WARN_ON_ONCE(trunc && !dax_layout_is_idle_page(page));
> WARN_ON_ONCE(page->mapping && page->mapping != mapping);
> page->mapping = NULL;
> page->index = 0;
> @@ -372,7 +372,7 @@ static struct page *dax_busy_page(void *entry)
> for_each_mapped_pfn(entry, pfn) {
> struct page *page = pfn_to_page(pfn);
>
> - if (page_ref_count(page) > 1)
> + if (!dax_layout_is_idle_page(page))
> return page;
> }
> return NULL;
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 771ed8b1fadb..132620cbfa13 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -3937,10 +3937,7 @@ int ext4_break_layouts(struct inode *inode)
> if (!page)
> return 0;
>
> - error = ___wait_var_event(&page->_refcount,
> - atomic_read(&page->_refcount) == 1,
> - TASK_INTERRUPTIBLE, 0, 0,
> - ext4_wait_dax_page(ei));
> + error = dax_wait_page(ei, page, ext4_wait_dax_page);
> } while (error == 0);
>
> return error;
> diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
> index 3d1b95124744..a5304aaeaa3a 100644
> --- a/fs/xfs/xfs_file.c
> +++ b/fs/xfs/xfs_file.c
> @@ -749,9 +749,7 @@ xfs_break_dax_layouts(
> return 0;
>
> *retry = true;
> - return ___wait_var_event(&page->_refcount,
> - atomic_read(&page->_refcount) == 1, TASK_INTERRUPTIBLE,
> - 0, 0, xfs_wait_dax_page(inode));
> + return dax_wait_page(inode, page, xfs_wait_dax_page);
I don't mind this open-coded soup getting cleaned up into a macro,
though my general opinion is that if the mm/dax developers are ok with
this then:
Acked-by: Darrick J. Wong <darrick.wong@oracle.com>
--D
> }
>
> int
> diff --git a/include/linux/dax.h b/include/linux/dax.h
> index b52f084aa643..8909a91cd381 100644
> --- a/include/linux/dax.h
> +++ b/include/linux/dax.h
> @@ -243,6 +243,16 @@ static inline bool dax_mapping(struct address_space *mapping)
> return mapping->host && IS_DAX(mapping->host);
> }
>
> +static inline bool dax_layout_is_idle_page(struct page *page)
> +{
> + return page_ref_count(page) == 1;
> +}
> +
> +#define dax_wait_page(_inode, _page, _wait_cb) \
> + ___wait_var_event(&(_page)->_refcount, \
> + dax_layout_is_idle_page(_page), \
> + TASK_INTERRUPTIBLE, 0, 0, _wait_cb(_inode))
> +
> #ifdef CONFIG_DEV_DAX_HMEM_DEVICES
> void hmem_register_device(int target_nid, struct resource *r);
> #else
> --
> 2.20.1
>
^ permalink raw reply [flat|nested] 7+ messages in thread