[PATCH v13 007/137] mm: Add folio_put()

Matthew Wilcox (Oracle)
2021-07-12T03:13:23Z

If we know we have a folio, we can call folio_put() instead of put_page()
and save the overhead of calling compound_head(). Also skips the
devmap checks.

This commit looks like it should be a no-op, but actually saves 684 bytes
of text with the distro-derived config that I'm testing. Some functions
grow a little while others shrink. I presume the compiler is making
different inlining decisions.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Acked-by: Jeff Layton <jlayton@kernel.org>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: William Kucharski <william.kucharski@oracle.com>
Reviewed-by: David Howells <dhowells@redhat.com>
---
include/linux/mm.h | 33 ++++++++++++++++++++++++++++-----
1 file changed, 28 insertions(+), 5 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 460e9805dd9f..c981e3b28eb0 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -749,6 +749,11 @@ static inline int put_page_testzero(struct page *page)
return page_ref_dec_and_test(page);
}

+static inline int folio_put_testzero(struct folio *folio)
+{
+ return put_page_testzero(&folio->page);
+}
+
/*
* Try to grab a ref unless the page has a refcount of zero, return false if
* that is the case.
@@ -1245,9 +1250,28 @@ static inline __must_check bool try_get_page(struct page *page)
return true;
}

+/**
+ * folio_put - Decrement the reference count on a folio.
+ * @folio: The folio.
+ *
+ * If the folio's reference count reaches zero, the memory will be
+ * released back to the page allocator and may be used by another
+ * allocation immediately. Do not access the memory or the struct folio
+ * after calling folio_put() unless you can be sure that it wasn't the
+ * last reference.
+ *
+ * Context: May be called in process or interrupt context, but not in NMI
+ * context. May be called while holding a spinlock.
+ */
+static inline void folio_put(struct folio *folio)
+{
+ if (folio_put_testzero(folio))
+ __put_page(&folio->page);
+}
+
static inline void put_page(struct page *page)
{
- page = compound_head(page);
+ struct folio *folio = page_folio(page);

/*
* For devmap managed pages we need to catch refcount transition from
@@ -1255,13 +1279,12 @@ static inline void put_page(struct page *page)
* need to inform the device driver through callback. See
* include/linux/memremap.h and HMM for details.
*/
- if (page_is_devmap_managed(page)) {
- put_devmap_managed_page(page);
+ if (page_is_devmap_managed(&folio->page)) {
+ put_devmap_managed_page(&folio->page);
return;
}

- if (put_page_testzero(page))
- __put_page(page);
+ folio_put(folio);
}

/*
--
2.30.2