Re: [PATCH v7 3/8] mm: factor helpers for memory_failure_dev_pagemap

["Darrick J. Wong" <djwong@kernel.org>]

On Fri, Sep 24, 2021 at 09:09:54PM +0800, Shiyang Ruan wrote:
> memory_failure_dev_pagemap code is a bit complex before introduce RMAP
> feature for fsdax.  So it is needed to factor some helper functions to
> simplify these code.
> 
> Signed-off-by: Shiyang Ruan <ruansy.fnst@fujitsu.com>

This looks like a reasonable hoist...
Reviewed-by: Darrick J. Wong <djwong@kernel.org>

--D

> ---
>  mm/memory-failure.c | 140 ++++++++++++++++++++++++--------------------
>  1 file changed, 76 insertions(+), 64 deletions(-)
> 
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index 54879c339024..8ff9b52823c0 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -1430,6 +1430,79 @@ static int try_to_split_thp_page(struct page *page, const char *msg)
>  	return 0;
>  }
>  
> +static void unmap_and_kill(struct list_head *to_kill, unsigned long pfn,
> +		struct address_space *mapping, pgoff_t index, int flags)
> +{
> +	struct to_kill *tk;
> +	unsigned long size = 0;
> +
> +	list_for_each_entry(tk, to_kill, nd)
> +		if (tk->size_shift)
> +			size = max(size, 1UL << tk->size_shift);
> +	if (size) {
> +		/*
> +		 * Unmap the largest mapping to avoid breaking up device-dax
> +		 * mappings which are constant size. The actual size of the
> +		 * mapping being torn down is communicated in siginfo, see
> +		 * kill_proc()
> +		 */
> +		loff_t start = (index << PAGE_SHIFT) & ~(size - 1);
> +
> +		unmap_mapping_range(mapping, start, size, 0);
> +	}
> +
> +	kill_procs(to_kill, flags & MF_MUST_KILL, false, pfn, flags);
> +}
> +
> +static int mf_generic_kill_procs(unsigned long long pfn, int flags,
> +		struct dev_pagemap *pgmap)
> +{
> +	struct page *page = pfn_to_page(pfn);
> +	LIST_HEAD(to_kill);
> +	dax_entry_t cookie;
> +
> +	/*
> +	 * Prevent the inode from being freed while we are interrogating
> +	 * the address_space, typically this would be handled by
> +	 * lock_page(), but dax pages do not use the page lock. This
> +	 * also prevents changes to the mapping of this pfn until
> +	 * poison signaling is complete.
> +	 */
> +	cookie = dax_lock_page(page);
> +	if (!cookie)
> +		return -EBUSY;
> +
> +	if (hwpoison_filter(page))
> +		return 0;
> +
> +	if (pgmap->type == MEMORY_DEVICE_PRIVATE) {
> +		/*
> +		 * TODO: Handle HMM pages which may need coordination
> +		 * with device-side memory.
> +		 */
> +		return -EBUSY;
> +	}
> +
> +	/*
> +	 * Use this flag as an indication that the dax page has been
> +	 * remapped UC to prevent speculative consumption of poison.
> +	 */
> +	SetPageHWPoison(page);
> +
> +	/*
> +	 * Unlike System-RAM there is no possibility to swap in a
> +	 * different physical page at a given virtual address, so all
> +	 * userspace consumption of ZONE_DEVICE memory necessitates
> +	 * SIGBUS (i.e. MF_MUST_KILL)
> +	 */
> +	flags |= MF_ACTION_REQUIRED | MF_MUST_KILL;
> +	collect_procs(page, &to_kill, true);
> +
> +	unmap_and_kill(&to_kill, pfn, page->mapping, page->index, flags);
> +	dax_unlock_page(page, cookie);
> +	return 0;
> +}
> +
>  static int memory_failure_hugetlb(unsigned long pfn, int flags)
>  {
>  	struct page *p = pfn_to_page(pfn);
> @@ -1519,12 +1592,8 @@ static int memory_failure_dev_pagemap(unsigned long pfn, int flags,
>  		struct dev_pagemap *pgmap)
>  {
>  	struct page *page = pfn_to_page(pfn);
> -	unsigned long size = 0;
> -	struct to_kill *tk;
>  	LIST_HEAD(tokill);
> -	int rc = -EBUSY;
> -	loff_t start;
> -	dax_entry_t cookie;
> +	int rc = -ENXIO;
>  
>  	if (flags & MF_COUNT_INCREASED)
>  		/*
> @@ -1533,67 +1602,10 @@ static int memory_failure_dev_pagemap(unsigned long pfn, int flags,
>  		put_page(page);
>  
>  	/* device metadata space is not recoverable */
> -	if (!pgmap_pfn_valid(pgmap, pfn)) {
> -		rc = -ENXIO;
> -		goto out;
> -	}
> -
> -	/*
> -	 * Prevent the inode from being freed while we are interrogating
> -	 * the address_space, typically this would be handled by
> -	 * lock_page(), but dax pages do not use the page lock. This
> -	 * also prevents changes to the mapping of this pfn until
> -	 * poison signaling is complete.
> -	 */
> -	cookie = dax_lock_page(page);
> -	if (!cookie)
> +	if (!pgmap_pfn_valid(pgmap, pfn))
>  		goto out;
>  
> -	if (hwpoison_filter(page)) {
> -		rc = 0;
> -		goto unlock;
> -	}
> -
> -	if (pgmap->type == MEMORY_DEVICE_PRIVATE) {
> -		/*
> -		 * TODO: Handle HMM pages which may need coordination
> -		 * with device-side memory.
> -		 */
> -		goto unlock;
> -	}
> -
> -	/*
> -	 * Use this flag as an indication that the dax page has been
> -	 * remapped UC to prevent speculative consumption of poison.
> -	 */
> -	SetPageHWPoison(page);
> -
> -	/*
> -	 * Unlike System-RAM there is no possibility to swap in a
> -	 * different physical page at a given virtual address, so all
> -	 * userspace consumption of ZONE_DEVICE memory necessitates
> -	 * SIGBUS (i.e. MF_MUST_KILL)
> -	 */
> -	flags |= MF_ACTION_REQUIRED | MF_MUST_KILL;
> -	collect_procs(page, &tokill, flags & MF_ACTION_REQUIRED);
> -
> -	list_for_each_entry(tk, &tokill, nd)
> -		if (tk->size_shift)
> -			size = max(size, 1UL << tk->size_shift);
> -	if (size) {
> -		/*
> -		 * Unmap the largest mapping to avoid breaking up
> -		 * device-dax mappings which are constant size. The
> -		 * actual size of the mapping being torn down is
> -		 * communicated in siginfo, see kill_proc()
> -		 */
> -		start = (page->index << PAGE_SHIFT) & ~(size - 1);
> -		unmap_mapping_range(page->mapping, start, size, 0);
> -	}
> -	kill_procs(&tokill, flags & MF_MUST_KILL, false, pfn, flags);
> -	rc = 0;
> -unlock:
> -	dax_unlock_page(page, cookie);
> +	rc = mf_generic_kill_procs(pfn, flags, pgmap);
>  out:
>  	/* drop pgmap ref acquired in caller */
>  	put_dev_pagemap(pgmap);
> -- 
> 2.33.0
> 
> 
>