[v10,2/9] mm: factor helpers for memory_failure_dev_pagemap

Commit Message

Shiyang Ruan Jan. 27, 2022, 12:40 p.m. UTC

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 <[e-mail]>
Reviewed-by: Darrick J. Wong <[e-mail]>
Reviewed-by: Christoph Hellwig <[e-mail]>
---
 mm/memory-failure.c | 141 ++++++++++++++++++++++++--------------------
 1 file changed, 77 insertions(+), 64 deletions(-)

Comments

Matthew Wilcox (Oracle) Feb. 1, 2022, 9:03 p.m. UTC | #1

On Thu, Jan 27, 2022 at 08:40:51PM +0800, Shiyang Ruan wrote:
> +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;
> +}

There's an assumption here that fsdax only has order-0 pages.
pfn_to_page() is going to return the precise page for that pfn, but then
page->mapping and page->index are not valid for tail pages.

I'm currently trying to folio-ise memory-failure.c, and it is not
going well!  There are several places where it's hard to tell
what should happen.

Dan Williams Feb. 15, 2022, 10:11 p.m. UTC | #2

On Thu, Jan 27, 2022 at 4:41 AM Shiyang Ruan <[e-mail]> 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 <[e-mail]>
> Reviewed-by: Darrick J. Wong <[e-mail]>
> Reviewed-by: Christoph Hellwig <[e-mail]>

Looks good,

Reviewed-by: Dan Williams <[e-mail]>

Patch

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 14ae5c18e776..98b6144e4b9b 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -1500,6 +1500,80 @@  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);
@@ -1576,12 +1650,8 @@  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)
 		/*
@@ -1590,67 +1660,10 @@  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);