[v14,071/138] mm/writeback: Add filemap_dirty_folio()

Commit Message

Matthew Wilcox July 15, 2021, 3:35 a.m. UTC

Reimplement __set_page_dirty_nobuffers() as a wrapper around
filemap_dirty_folio().

Signed-off-by: Matthew Wilcox (Oracle) <[e-mail]>
Reviewed-by: Christoph Hellwig <[e-mail]>
---
 include/linux/writeback.h |  1 +
 mm/folio-compat.c         |  6 ++++
 mm/page-writeback.c       | 60 ++++++++++++++++++++-------------------
 3 files changed, 38 insertions(+), 29 deletions(-)

Comments

David Howells Aug. 10, 2021, 9:21 p.m. UTC | #1

Matthew Wilcox (Oracle) <[e-mail]> wrote:

> Reimplement __set_page_dirty_nobuffers() as a wrapper around
> filemap_dirty_folio().
> 
> Signed-off-by: Matthew Wilcox (Oracle) <[e-mail]>
> Reviewed-by: Christoph Hellwig <[e-mail]>

Reviewed-by: David Howells <[e-mail]>

Vlastimil Babka Aug. 12, 2021, 4:07 p.m. UTC | #2

On 7/15/21 5:35 AM, Matthew Wilcox (Oracle) wrote:
> Reimplement __set_page_dirty_nobuffers() as a wrapper around
> filemap_dirty_folio().

I assume it becomes obvious later why the new "mapping" parameter instead of
taking it from the folio, but maybe the changelog should say it here?

> Signed-off-by: Matthew Wilcox (Oracle) <[e-mail]>
> Reviewed-by: Christoph Hellwig <[e-mail]>

Acked-by: Vlastimil Babka <[e-mail]>

Matthew Wilcox Aug. 15, 2021, 3:31 a.m. UTC | #3

On Thu, Aug 12, 2021 at 06:07:05PM +0200, Vlastimil Babka wrote:
> On 7/15/21 5:35 AM, Matthew Wilcox (Oracle) wrote:
> > Reimplement __set_page_dirty_nobuffers() as a wrapper around
> > filemap_dirty_folio().
> 
> I assume it becomes obvious later why the new "mapping" parameter instead of
> taking it from the folio, but maybe the changelog should say it here?

---

mm/writeback: Add filemap_dirty_folio()

Reimplement __set_page_dirty_nobuffers() as a wrapper around
filemap_dirty_folio().  Eventually folio_mark_dirty() will pass
the folio's mapping to the address space's ->dirty_folio()
operation, so add the parameter to filemap_dirty_folio() now.

---

Nobody seems quite sure whether it's possible to truncate (or otherwise
remove) a page from a file while it's being marked as dirty.  viz:

int set_page_dirty(struct page *page)
{
        struct address_space *mapping = page_mapping(page);
        if (likely(mapping)) {
...
                return mapping->a_ops->set_page_dirty(page);
}

so ->set_page_dirty can only be called if page has a mapping (obviously,
otherwise we wouldn't know whose ->set_page_dirty to call).  But then
in __set_page_dirty_nobuffers(), we check to see if mapping has
become unset:

        if (!TestSetPageDirty(page)) {
                struct address_space *mapping = page_mapping(page);

                if (!mapping) {
                        unlock_page_memcg(page);
                        return 1;
                }

Confusingly, the comment to __set_page_dirty_nobuffers says:

 * The caller must ensure this doesn't race with truncation.  Most will simply
 * hold the page lock, but e.g. zap_pte_range() calls with the page mapped and
 * the pte lock held, which also locks out truncation.

I believe this is left-over from commit 2d6d7f982846 in 2015.

Anyway, passing mapping as a parameter is something we already do for
just about every other address_space operation, and we already called
page_mapping() to get it, so why make the callee call it again?  Not to
mention people get confused about whether to call page_mapping() or just
look at page->mapping.  Changing the ->set_page_dirty() operation to
->dirty_folio() is something I've postponed until the 5.17/5.18 timeframe,
but we might as well pass the parameter to filemap_dirty_folio() now.

Patch

diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index 667e86cfbdcf..eda9cc778ef6 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -398,6 +398,7 @@  void writeback_set_ratelimit(void);
 void tag_pages_for_writeback(struct address_space *mapping,
 			     pgoff_t start, pgoff_t end);
 
+bool filemap_dirty_folio(struct address_space *mapping, struct folio *folio);
 void account_page_redirty(struct page *page);
 
 void sb_mark_inode_writeback(struct inode *inode);
diff --git a/mm/folio-compat.c b/mm/folio-compat.c
index 2c2b3917b5dc..dad962b920e5 100644
--- a/mm/folio-compat.c
+++ b/mm/folio-compat.c
@@ -83,3 +83,9 @@  bool set_page_dirty(struct page *page)
 	return folio_mark_dirty(page_folio(page));
 }
 EXPORT_SYMBOL(set_page_dirty);
+
+int __set_page_dirty_nobuffers(struct page *page)
+{
+	return filemap_dirty_folio(page_mapping(page), page_folio(page));
+}
+EXPORT_SYMBOL(__set_page_dirty_nobuffers);
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 2dc410b110ff..bd97c461d499 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -2488,41 +2488,43 @@  void __folio_mark_dirty(struct folio *folio, struct address_space *mapping,
 	xa_unlock_irqrestore(&mapping->i_pages, flags);
 }
 
-/*
- * For address_spaces which do not use buffers.  Just tag the page as dirty in
- * the xarray.
- *
- * This is also used when a single buffer is being dirtied: we want to set the
- * page dirty in that case, but not all the buffers.  This is a "bottom-up"
- * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying.
- *
- * The caller must ensure this doesn't race with truncation.  Most will simply
- * hold the page lock, but e.g. zap_pte_range() calls with the page mapped and
- * the pte lock held, which also locks out truncation.
+/**
+ * filemap_dirty_folio - Mark a folio dirty for filesystems which do not use buffer_heads.
+ * @mapping: Address space this folio belongs to.
+ * @folio: Folio to be marked as dirty.
+ *
+ * Filesystems which do not use buffer heads should call this function
+ * from their set_page_dirty address space operation.  It ignores the
+ * contents of folio_get_private(), so if the filesystem marks individual
+ * blocks as dirty, the filesystem should handle that itself.
+ *
+ * This is also sometimes used by filesystems which use buffer_heads when
+ * a single buffer is being dirtied: we want to set the folio dirty in
+ * that case, but not all the buffers.  This is a "bottom-up" dirtying,
+ * whereas __set_page_dirty_buffers() is a "top-down" dirtying.
+ *
+ * The caller must ensure this doesn't race with truncation.  Most will
+ * simply hold the folio lock, but e.g. zap_pte_range() calls with the
+ * folio mapped and the pte lock held, which also locks out truncation.
  */
-int __set_page_dirty_nobuffers(struct page *page)
+bool filemap_dirty_folio(struct address_space *mapping, struct folio *folio)
 {
-	lock_page_memcg(page);
-	if (!TestSetPageDirty(page)) {
-		struct address_space *mapping = page_mapping(page);
+	folio_memcg_lock(folio);
+	if (folio_test_set_dirty(folio)) {
+		folio_memcg_unlock(folio);
+		return false;
+	}
 
-		if (!mapping) {
-			unlock_page_memcg(page);
-			return 1;
-		}
-		__set_page_dirty(page, mapping, !PagePrivate(page));
-		unlock_page_memcg(page);
+	__folio_mark_dirty(folio, mapping, !folio_test_private(folio));
+	folio_memcg_unlock(folio);
 
-		if (mapping->host) {
-			/* !PageAnon && !swapper_space */
-			__mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
-		}
-		return 1;
+	if (mapping->host) {
+		/* !PageAnon && !swapper_space */
+		__mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
 	}
-	unlock_page_memcg(page);
-	return 0;
+	return true;
 }
-EXPORT_SYMBOL(__set_page_dirty_nobuffers);
+EXPORT_SYMBOL(filemap_dirty_folio);
 
 /*
  * Call this whenever redirtying a page, to de-account the dirty counters