diff mbox series

[RFC] mm: Split page_has_private() in two to better handle PG_private_2

Message ID 136646.1617916529@warthog.procyon.org.uk (mailing list archive)
State New
Headers show
Series [RFC] mm: Split page_has_private() in two to better handle PG_private_2 | expand

Commit Message

David Howells April 8, 2021, 9:15 p.m. UTC
Hi Willy, Linus,

How about this to handle the situation with PG_private_2?  I think it handles
things according to Linus's suggestion.

David
---
mm: Split page_has_private() in two to better handle PG_private_2

Split page_has_private() into two functions:

 (1) page_needs_cleanup() to find out if a page needs the ->releasepage(),
     ->invalidatepage(), etc. address space ops calling upon it.

     This returns true when either PG_private or PG_private_2 are set.

 (2) page_private_count() which returns a count of the number of refs
     contributed to a page for attached private data.

     This returns 1 if PG_private is set and 0 otherwise.

I think the suggestion[1] is that PG_private_2 should just have a ref on
the page, but this isn't accounted in the same way as PG_private's ref.

Notes:

 (*) The following:

        btrfs_migratepage()
        iomap_set_range_uptodate()
        iomap_migrate_page()
        to_iomap_page()

     should probably all use PagePrivate() rather than page_has_private()
     since they're interested in what's attached to page->private when
     they're doing this, and not PG_private_2.

     It may not matter in these cases since page->private is probably NULL
     if PG_private is not set.

 (*) Do we actually need PG_private, or is it possible just to see if
     page->private is NULL?

 (*) There's a lot of "if (page_has_private()) try_to_release_page()"
     combos.  Does it make sense to create a inline function for this?

Signed-off-by: David Howells <dhowells@redhat.com>
Link: https://lore.kernel.org/linux-fsdevel/CAHk-=whWoJhGeMn85LOh9FX-5d2-Upzmv1m2ZmYxvD31TKpUTA@mail.gmail.com/ [1]
---
 fs/btrfs/disk-io.c             |    2 +-
 fs/btrfs/inode.c               |    2 +-
 fs/ext4/move_extent.c          |    8 ++++----
 fs/fuse/dev.c                  |    2 +-
 fs/iomap/buffered-io.c         |    6 +++---
 fs/splice.c                    |    2 +-
 include/linux/page-flags.h     |   17 +++++++++++++++--
 include/trace/events/pagemap.h |    2 +-
 mm/khugepaged.c                |    4 ++--
 mm/migrate.c                   |   10 +++++-----
 mm/readahead.c                 |    2 +-
 mm/truncate.c                  |   12 ++++++------
 mm/vmscan.c                    |   12 ++++++------
 13 files changed, 47 insertions(+), 34 deletions(-)

Comments

Linus Torvalds April 8, 2021, 11:50 p.m. UTC | #1
On Thu, Apr 8, 2021 at 2:15 PM David Howells <dhowells@redhat.com> wrote:
>
> mm: Split page_has_private() in two to better handle PG_private_2

From a look through the patch and some (limited) thinking about it, I
like the patch. I think it clarifies the two very different cases, and
makes it clear that one is about that page cleanup, and the other is
about the magical reference counting. The two are separate issues,
even if for PG_private both happen to be true.

So this seems sane to me.

That said, I had a couple of reactions:

> diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
> index 04a34c08e0a6..04cb440ce06e 100644
> --- a/include/linux/page-flags.h
> +++ b/include/linux/page-flags.h
> @@ -832,14 +832,27 @@ static inline void ClearPageSlabPfmemalloc(struct page *page)
>
>  #define PAGE_FLAGS_PRIVATE                             \
>         (1UL << PG_private | 1UL << PG_private_2)

I think this should be re-named to be PAGE_FLAGS_CLEANUP, because I
don't think it makes any other sense to "combine" the two PG_private*
bits any more. No?

> +static inline int page_private_count(struct page *page)
> +{
> +       return test_bit(PG_private, &page->flags) ? 1 : 0;
> +}

Why is this open-coding the bit test, rather than just doing

        return PagePrivate(page) ? 1 : 0;

instead? In fact, since test_bit() _should_ return a 'bool', I think even just

        return PagePrivate(page);

should work and give the same result, but I could imagine that some
architecture version of "test_bit()" might return some other non-zero
value (although honestly, I think that should be fixed if so).

                Linus
David Howells April 9, 2021, 8:14 a.m. UTC | #2
Linus Torvalds <torvalds@linux-foundation.org> wrote:

> >  #define PAGE_FLAGS_PRIVATE                             \
> >         (1UL << PG_private | 1UL << PG_private_2)
>
> I think this should be re-named to be PAGE_FLAGS_CLEANUP, because I
> don't think it makes any other sense to "combine" the two PG_private*
> bits any more. No?

Sure.  Do we even want it still, or should I just fold it into
page_needs_cleanup()?  It seems to be the only place it's used.

> > +static inline int page_private_count(struct page *page)
> > +{
> > +       return test_bit(PG_private, &page->flags) ? 1 : 0;
> > +}
>
> Why is this open-coding the bit test, rather than just doing
>
>         return PagePrivate(page) ? 1 : 0;
>
> instead? In fact, since test_bit() _should_ return a 'bool', I think even just
>
>         return PagePrivate(page);

Sorry, yes, it should be that.  I was looking at transforming the "1 <<
PG_private" and completely overlooked that this should be PagePrivate().

> should work and give the same result, but I could imagine that some
> architecture version of "test_bit()" might return some other non-zero
> value (although honestly, I think that should be fixed if so).

Yeah.  I seem to recall that test_bit() on some arches used to return the
datum just with the other bits masked off, but I may be misremembering.

In asm-generic/bitops/non-atomic.h:

static inline int test_bit(int nr, const volatile unsigned long *addr)
{
	return 1UL & (addr[BIT_WORD(nr)] >> (nr & (BITS_PER_LONG-1)));
}

should perhaps return bool?

I wonder, should:

	static __always_inline int PageTail(struct page *page)
	static __always_inline int PageCompound(struct page *page)
	static __always_inline int Page##uname(struct page *page)
	static __always_inline int TestSetPage##uname(struct page *page)
	static __always_inline int TestClearPage##uname(struct page *page)

also all return bool?

David
diff mbox series

Patch

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 41b718cfea40..d95f8d4b3004 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -936,7 +936,7 @@  static int btree_migratepage(struct address_space *mapping,
 	 * Buffers may be managed in a filesystem specific way.
 	 * We must have no buffers or drop them.
 	 */
-	if (page_has_private(page) &&
+	if (page_needs_cleanup(page) &&
 	    !try_to_release_page(page, GFP_KERNEL))
 		return -EAGAIN;
 	return migrate_page(mapping, newpage, page, mode);
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 7cdf65be3707..94f038d34f16 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -8333,7 +8333,7 @@  static int btrfs_migratepage(struct address_space *mapping,
 	if (ret != MIGRATEPAGE_SUCCESS)
 		return ret;
 
-	if (page_has_private(page))
+	if (PagePrivate(page))
 		attach_page_private(newpage, detach_page_private(page));
 
 	if (PagePrivate2(page)) {
diff --git a/fs/ext4/move_extent.c b/fs/ext4/move_extent.c
index 64a579734f93..16d0a7a73191 100644
--- a/fs/ext4/move_extent.c
+++ b/fs/ext4/move_extent.c
@@ -329,9 +329,9 @@  move_extent_per_page(struct file *o_filp, struct inode *donor_inode,
 			ext4_double_up_write_data_sem(orig_inode, donor_inode);
 			goto data_copy;
 		}
-		if ((page_has_private(pagep[0]) &&
+		if ((page_needs_cleanup(pagep[0]) &&
 		     !try_to_release_page(pagep[0], 0)) ||
-		    (page_has_private(pagep[1]) &&
+		    (page_needs_cleanup(pagep[1]) &&
 		     !try_to_release_page(pagep[1], 0))) {
 			*err = -EBUSY;
 			goto drop_data_sem;
@@ -351,8 +351,8 @@  move_extent_per_page(struct file *o_filp, struct inode *donor_inode,
 
 	/* At this point all buffers in range are uptodate, old mapping layout
 	 * is no longer required, try to drop it now. */
-	if ((page_has_private(pagep[0]) && !try_to_release_page(pagep[0], 0)) ||
-	    (page_has_private(pagep[1]) && !try_to_release_page(pagep[1], 0))) {
+	if ((page_needs_cleanup(pagep[0]) && !try_to_release_page(pagep[0], 0)) ||
+	    (page_needs_cleanup(pagep[1]) && !try_to_release_page(pagep[1], 0))) {
 		*err = -EBUSY;
 		goto unlock_pages;
 	}
diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index c0fee830a34e..76e8ca9e47fa 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -837,7 +837,7 @@  static int fuse_try_move_page(struct fuse_copy_state *cs, struct page **pagep)
 	 */
 	if (WARN_ON(page_mapped(oldpage)))
 		goto out_fallback_unlock;
-	if (WARN_ON(page_has_private(oldpage)))
+	if (WARN_ON(page_needs_cleanup(oldpage)))
 		goto out_fallback_unlock;
 	if (WARN_ON(PageDirty(oldpage) || PageWriteback(oldpage)))
 		goto out_fallback_unlock;
diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index 414769a6ad11..9c89db033548 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -41,7 +41,7 @@  static inline struct iomap_page *to_iomap_page(struct page *page)
 	 */
 	VM_BUG_ON_PGFLAGS(PageTail(page), page);
 
-	if (page_has_private(page))
+	if (page_needs_cleanup(page))
 		return (struct iomap_page *)page_private(page);
 	return NULL;
 }
@@ -163,7 +163,7 @@  iomap_set_range_uptodate(struct page *page, unsigned off, unsigned len)
 	if (PageError(page))
 		return;
 
-	if (page_has_private(page))
+	if (PagePrivate(page))
 		iomap_iop_set_range_uptodate(page, off, len);
 	else
 		SetPageUptodate(page);
@@ -502,7 +502,7 @@  iomap_migrate_page(struct address_space *mapping, struct page *newpage,
 	if (ret != MIGRATEPAGE_SUCCESS)
 		return ret;
 
-	if (page_has_private(page))
+	if (PagePrivate(page))
 		attach_page_private(newpage, detach_page_private(page));
 
 	if (mode != MIGRATE_SYNC_NO_COPY)
diff --git a/fs/splice.c b/fs/splice.c
index 5dbce4dcc1a7..bf102bc947bb 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -65,7 +65,7 @@  static bool page_cache_pipe_buf_try_steal(struct pipe_inode_info *pipe,
 		 */
 		wait_on_page_writeback(page);
 
-		if (page_has_private(page) &&
+		if (page_needs_cleanup(page) &&
 		    !try_to_release_page(page, GFP_KERNEL))
 			goto out_unlock;
 
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 04a34c08e0a6..04cb440ce06e 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -832,14 +832,27 @@  static inline void ClearPageSlabPfmemalloc(struct page *page)
 
 #define PAGE_FLAGS_PRIVATE				\
 	(1UL << PG_private | 1UL << PG_private_2)
+
+/**
+ * page_private_count - Find out how many refs a page's private data contribute
+ * @page: The page to be checked
+ *
+ * Return the contribution to the pagecount of the private data attached to a
+ * page.
+ */
+static inline int page_private_count(struct page *page)
+{
+	return test_bit(PG_private, &page->flags) ? 1 : 0;
+}
+
 /**
- * page_has_private - Determine if page has private stuff
+ * page_needs_cleanup - Determine if page has private stuff that needs cleaning
  * @page: The page to be checked
  *
  * Determine if a page has private stuff, indicating that release routines
  * should be invoked upon it.
  */
-static inline int page_has_private(struct page *page)
+static inline int page_needs_cleanup(struct page *page)
 {
 	return !!(page->flags & PAGE_FLAGS_PRIVATE);
 }
diff --git a/include/trace/events/pagemap.h b/include/trace/events/pagemap.h
index e1735fe7c76a..3ff3404cc399 100644
--- a/include/trace/events/pagemap.h
+++ b/include/trace/events/pagemap.h
@@ -22,7 +22,7 @@ 
 	(PageSwapCache(page)	? PAGEMAP_SWAPCACHE  : 0) | \
 	(PageSwapBacked(page)	? PAGEMAP_SWAPBACKED : 0) | \
 	(PageMappedToDisk(page)	? PAGEMAP_MAPPEDDISK : 0) | \
-	(page_has_private(page) ? PAGEMAP_BUFFERS    : 0) \
+	(page_needs_cleanup(page) ? PAGEMAP_BUFFERS    : 0) \
 	)
 
 TRACE_EVENT(mm_lru_insertion,
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index a7d6cb912b05..d3b60a31aae2 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1822,7 +1822,7 @@  static void collapse_file(struct mm_struct *mm,
 			goto out_unlock;
 		}
 
-		if (page_has_private(page) &&
+		if (page_needs_cleanup(page) &&
 		    !try_to_release_page(page, GFP_KERNEL)) {
 			result = SCAN_PAGE_HAS_PRIVATE;
 			putback_lru_page(page);
@@ -2019,7 +2019,7 @@  static void khugepaged_scan_file(struct mm_struct *mm,
 		}
 
 		if (page_count(page) !=
-		    1 + page_mapcount(page) + page_has_private(page)) {
+		    1 + page_mapcount(page) + page_private_count(page)) {
 			result = SCAN_PAGE_COUNT;
 			break;
 		}
diff --git a/mm/migrate.c b/mm/migrate.c
index 62b81d5257aa..eafd73bea945 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -382,7 +382,7 @@  static int expected_page_refs(struct address_space *mapping, struct page *page)
 	 */
 	expected_count += is_device_private_page(page);
 	if (mapping)
-		expected_count += thp_nr_pages(page) + page_has_private(page);
+		expected_count += thp_nr_pages(page) + page_private_count(page);
 
 	return expected_count;
 }
@@ -530,7 +530,7 @@  int migrate_huge_page_move_mapping(struct address_space *mapping,
 	int expected_count;
 
 	xas_lock_irq(&xas);
-	expected_count = 2 + page_has_private(page);
+	expected_count = 2 + page_private_count(page);
 	if (page_count(page) != expected_count || xas_load(&xas) != page) {
 		xas_unlock_irq(&xas);
 		return -EAGAIN;
@@ -924,7 +924,7 @@  static int fallback_migrate_page(struct address_space *mapping,
 	 * Buffers may be managed in a filesystem specific way.
 	 * We must have no buffers or drop them.
 	 */
-	if (page_has_private(page) &&
+	if (page_needs_cleanup(page) &&
 	    !try_to_release_page(page, GFP_KERNEL))
 		return mode == MIGRATE_SYNC ? -EAGAIN : -EBUSY;
 
@@ -1117,7 +1117,7 @@  static int __unmap_and_move(struct page *page, struct page *newpage,
 	 */
 	if (!page->mapping) {
 		VM_BUG_ON_PAGE(PageAnon(page), page);
-		if (page_has_private(page)) {
+		if (page_needs_cleanup(page)) {
 			try_to_free_buffers(page);
 			goto out_unlock_both;
 		}
@@ -2618,7 +2618,7 @@  static bool migrate_vma_check_page(struct page *page)
 
 	/* For file back page */
 	if (page_mapping(page))
-		extra += 1 + page_has_private(page);
+		extra += 1 + page_private_count(page);
 
 	if ((page_count(page) - extra) > page_mapcount(page))
 		return false;
diff --git a/mm/readahead.c b/mm/readahead.c
index f02dbebf1cef..661295ec4669 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -48,7 +48,7 @@  EXPORT_SYMBOL_GPL(file_ra_state_init);
 static void read_cache_pages_invalidate_page(struct address_space *mapping,
 					     struct page *page)
 {
-	if (page_has_private(page)) {
+	if (page_needs_cleanup(page)) {
 		if (!trylock_page(page))
 			BUG();
 		page->mapping = mapping;
diff --git a/mm/truncate.c b/mm/truncate.c
index 455944264663..7cad4c79686b 100644
--- a/mm/truncate.c
+++ b/mm/truncate.c
@@ -176,7 +176,7 @@  truncate_cleanup_page(struct address_space *mapping, struct page *page)
 		unmap_mapping_pages(mapping, page->index, nr, false);
 	}
 
-	if (page_has_private(page))
+	if (page_needs_cleanup(page))
 		do_invalidatepage(page, 0, thp_size(page));
 
 	/*
@@ -204,7 +204,7 @@  invalidate_complete_page(struct address_space *mapping, struct page *page)
 	if (page->mapping != mapping)
 		return 0;
 
-	if (page_has_private(page) && !try_to_release_page(page, 0))
+	if (page_needs_cleanup(page) && !try_to_release_page(page, 0))
 		return 0;
 
 	ret = remove_mapping(mapping, page);
@@ -346,7 +346,7 @@  void truncate_inode_pages_range(struct address_space *mapping,
 			wait_on_page_writeback(page);
 			zero_user_segment(page, partial_start, top);
 			cleancache_invalidate_page(mapping, page);
-			if (page_has_private(page))
+			if (page_needs_cleanup(page))
 				do_invalidatepage(page, partial_start,
 						  top - partial_start);
 			unlock_page(page);
@@ -359,7 +359,7 @@  void truncate_inode_pages_range(struct address_space *mapping,
 			wait_on_page_writeback(page);
 			zero_user_segment(page, 0, partial_end);
 			cleancache_invalidate_page(mapping, page);
-			if (page_has_private(page))
+			if (page_needs_cleanup(page))
 				do_invalidatepage(page, 0,
 						  partial_end);
 			unlock_page(page);
@@ -581,14 +581,14 @@  invalidate_complete_page2(struct address_space *mapping, struct page *page)
 	if (page->mapping != mapping)
 		return 0;
 
-	if (page_has_private(page) && !try_to_release_page(page, GFP_KERNEL))
+	if (page_needs_cleanup(page) && !try_to_release_page(page, GFP_KERNEL))
 		return 0;
 
 	xa_lock_irqsave(&mapping->i_pages, flags);
 	if (PageDirty(page))
 		goto failed;
 
-	BUG_ON(page_has_private(page));
+	BUG_ON(page_needs_cleanup(page));
 	__delete_from_page_cache(page, NULL);
 	xa_unlock_irqrestore(&mapping->i_pages, flags);
 
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 562e87cbd7a1..4d9928e3446d 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -725,7 +725,7 @@  static inline int is_page_cache_freeable(struct page *page)
 	 * heads at page->private.
 	 */
 	int page_cache_pins = thp_nr_pages(page);
-	return page_count(page) - page_has_private(page) == 1 + page_cache_pins;
+	return page_count(page) - page_private_count(page) == 1 + page_cache_pins;
 }
 
 static int may_write_to_inode(struct inode *inode)
@@ -801,7 +801,7 @@  static pageout_t pageout(struct page *page, struct address_space *mapping)
 		 * Some data journaling orphaned pages can have
 		 * page->mapping == NULL while being dirty with clean buffers.
 		 */
-		if (page_has_private(page)) {
+		if (page_needs_cleanup(page)) {
 			if (try_to_free_buffers(page)) {
 				ClearPageDirty(page);
 				pr_info("%s: orphaned page\n", __func__);
@@ -1057,7 +1057,7 @@  static void page_check_dirty_writeback(struct page *page,
 	*writeback = PageWriteback(page);
 
 	/* Verify dirty/writeback state if the filesystem supports it */
-	if (!page_has_private(page))
+	if (!page_needs_cleanup(page))
 		return;
 
 	mapping = page_mapping(page);
@@ -1399,7 +1399,7 @@  static unsigned int shrink_page_list(struct list_head *page_list,
 		 * process address space (page_count == 1) it can be freed.
 		 * Otherwise, leave the page on the LRU so it is swappable.
 		 */
-		if (page_has_private(page)) {
+		if (page_needs_cleanup(page)) {
 			if (!try_to_release_page(page, sc->gfp_mask))
 				goto activate_locked;
 			if (!mapping && page_count(page) == 1) {
@@ -2050,8 +2050,8 @@  static void shrink_active_list(unsigned long nr_to_scan,
 		}
 
 		if (unlikely(buffer_heads_over_limit)) {
-			if (page_has_private(page) && trylock_page(page)) {
-				if (page_has_private(page))
+			if (page_needs_cleanup(page) && trylock_page(page)) {
+				if (page_needs_cleanup(page))
 					try_to_release_page(page, 0);
 				unlock_page(page);
 			}