[v3,02/23] filemap: Added filemap_get_folios_tag()

Commit Message

Vishal Moola (Oracle) Oct. 17, 2022, 8:24 p.m. UTC

This is the equivalent of find_get_pages_range_tag(), except for folios
instead of pages.

One noteable difference is filemap_get_folios_tag() does not take in a
maximum pages argument. It instead tries to fill a folio batch and stops
either once full (15 folios) or reaching the end of the search range.

The new function supports large folios, the initial function did not
since all callers don't use large folios.

Signed-off-by: Vishal Moola (Oracle) <[e-mail]>
---
 include/linux/pagemap.h |  2 ++
 mm/filemap.c            | 53 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 55 insertions(+)

Comments

Matthew Wilcox Oct. 24, 2022, 7:42 p.m. UTC | #1

On Mon, Oct 17, 2022 at 01:24:30PM -0700, Vishal Moola (Oracle) wrote:
> This is the equivalent of find_get_pages_range_tag(), except for folios
> instead of pages.
> 
> One noteable difference is filemap_get_folios_tag() does not take in a
> maximum pages argument. It instead tries to fill a folio batch and stops
> either once full (15 folios) or reaching the end of the search range.
> 
> The new function supports large folios, the initial function did not
> since all callers don't use large folios.

Reviewed-by: Matthew Wilcow (Oracle) <[e-mail]>

> +/**
> + * filemap_get_folios_tag - Get a batch of folios matching @tag.
> + * @mapping:    The address_space to search
> + * @start:      The starting page index
> + * @end:        The final page index (inclusive)
> + * @tag:        The tag index
> + * @fbatch:     The batch to fill
> + *
> + * Same as filemap_get_folios, but only returning folios tagged with @tag

If you add () after filemap_get_folios, it turns into a nice link in
the html documentation.

> + *
> + * Return: The number of folios found

Missing full stop at the end of this line.

> + * Also update @start to index the next folio for traversal

Ditto.

> + */
> +unsigned filemap_get_folios_tag(struct address_space *mapping, pgoff_t *start,
> +			pgoff_t end, xa_mark_t tag, struct folio_batch *fbatch)
> +{
> +	XA_STATE(xas, &mapping->i_pages, *start);
> +	struct folio *folio;
> +
> +	rcu_read_lock();
> +	while ((folio = find_get_entry(&xas, end, tag)) != NULL) {
> +		/* Shadow entries should never be tagged, but this iteration
> +		 * is lockless so there is a window for page reclaim to evict
> +		 * a page we saw tagged. Skip over it.
> +		 */

For multiline comments, the "/*" should be on a line by itself.

Patch

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 74d87e37a142..28275eecb949 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -740,6 +740,8 @@  unsigned filemap_get_folios(struct address_space *mapping, pgoff_t *start,
 		pgoff_t end, struct folio_batch *fbatch);
 unsigned filemap_get_folios_contig(struct address_space *mapping,
 		pgoff_t *start, pgoff_t end, struct folio_batch *fbatch);
+unsigned filemap_get_folios_tag(struct address_space *mapping, pgoff_t *start,
+		pgoff_t end, xa_mark_t tag, struct folio_batch *fbatch);
 unsigned find_get_pages_range_tag(struct address_space *mapping, pgoff_t *index,
 			pgoff_t end, xa_mark_t tag, unsigned int nr_pages,
 			struct page **pages);
diff --git a/mm/filemap.c b/mm/filemap.c
index 08341616ae7a..aa6e90ab0551 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2262,6 +2262,59 @@  unsigned filemap_get_folios_contig(struct address_space *mapping,
 }
 EXPORT_SYMBOL(filemap_get_folios_contig);
 
+/**
+ * filemap_get_folios_tag - Get a batch of folios matching @tag.
+ * @mapping:    The address_space to search
+ * @start:      The starting page index
+ * @end:        The final page index (inclusive)
+ * @tag:        The tag index
+ * @fbatch:     The batch to fill
+ *
+ * Same as filemap_get_folios, but only returning folios tagged with @tag
+ *
+ * Return: The number of folios found
+ * Also update @start to index the next folio for traversal
+ */
+unsigned filemap_get_folios_tag(struct address_space *mapping, pgoff_t *start,
+			pgoff_t end, xa_mark_t tag, struct folio_batch *fbatch)
+{
+	XA_STATE(xas, &mapping->i_pages, *start);
+	struct folio *folio;
+
+	rcu_read_lock();
+	while ((folio = find_get_entry(&xas, end, tag)) != NULL) {
+		/* Shadow entries should never be tagged, but this iteration
+		 * is lockless so there is a window for page reclaim to evict
+		 * a page we saw tagged. Skip over it.
+		 */
+		if (xa_is_value(folio))
+			continue;
+		if (!folio_batch_add(fbatch, folio)) {
+			unsigned long nr = folio_nr_pages(folio);
+
+			if (folio_test_hugetlb(folio))
+				nr = 1;
+			*start = folio->index + nr;
+			goto out;
+		}
+	}
+	/*
+	 * We come here when there is no page beyond @end. We take care to not
+	 * overflow the index @start as it confuses some of the callers. This
+	 * breaks the iteration when there is a page at index -1 but that is
+	 * already broke anyway.
+	 */
+	if (end == (pgoff_t)-1)
+		*start = (pgoff_t)-1;
+	else
+		*start = end + 1;
+out:
+	rcu_read_unlock();
+
+	return folio_batch_count(fbatch);
+}
+EXPORT_SYMBOL(filemap_get_folios_tag);
+
 /**
  * find_get_pages_range_tag - Find and return head pages matching @tag.
  * @mapping:	the address_space to search