mm: make folios_put() the basis of release_pages()

Patch series "Rearrange batched folio freeing", v3.

Other than the obvious "remove calls to compound_head" changes, the
fundamental belief here is that iterating a linked list is much slower
than iterating an array (5-15x slower in my testing).  There's also an
associated belief that since we iterate the batch of folios three times,
we do better when the array is small (ie 15 entries) than we do with a
batch that is hundreds of entries long, which only gives us the
opportunity for the first pages to fall out of cache by the time we get to
the end.

It is possible we should increase the size of folio_batch.  Hopefully the
bots let us know if this introduces any performance regressions.


This patch (of 3):

By making release_pages() call folios_put(), we can get rid of the calls
to compound_head() for the callers that already know they have folios.  We
can also get rid of the lock_batch tracking as we know the size of the
batch is limited by folio_batch.  This does reduce the maximum number of
pages for which the lruvec lock is held, from SWAP_CLUSTER_MAX (32) to
PAGEVEC_SIZE (15).  I do not expect this to make a significant difference,
but if it does, we can increase PAGEVEC_SIZE to 31.

Link: https://lkml.kernel.org/r/20240227174254.710559-1-willy@infradead.org
Link: https://lkml.kernel.org/r/20240227174254.710559-2-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 10 insertions, 6 deletions

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 49e22a2f6ccc..5c57fde9b69b 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -36,6 +36,7 @@ struct anon_vma;
 struct anon_vma_chain;
 struct user_struct;
 struct pt_regs;
+struct folio_batch;
 
 extern int sysctl_page_lock_unfairness;
 
@@ -1512,6 +1513,8 @@ static inline void folio_put_refs(struct folio *folio, int refs)
 		__folio_put(folio);
 }
 
+void folios_put_refs(struct folio_batch *folios, unsigned int *refs);
+
 /*
  * union release_pages_arg - an array of pages or folios
  *
@@ -1534,18 +1537,19 @@ void release_pages(release_pages_arg, int nr);
 /**
  * folios_put - Decrement the reference count on an array of folios.
  * @folios: The folios.
- * @nr: How many folios there are.
  *
- * Like folio_put(), but for an array of folios.  This is more efficient
- * than writing the loop yourself as it will optimise the locks which
- * need to be taken if the folios are freed.
+ * Like folio_put(), but for a batch of folios.  This is more efficient
+ * than writing the loop yourself as it will optimise the locks which need
+ * to be taken if the folios are freed.  The folios batch is returned
+ * empty and ready to be reused for another batch; there is no need to
+ * reinitialise it.
  *
  * Context: May be called in process or interrupt context, but not in NMI
  * context.  May be called while holding a spinlock.
  */
-static inline void folios_put(struct folio **folios, unsigned int nr)
+static inline void folios_put(struct folio_batch *folios)
 {
-	release_pages(folios, nr);
+	folios_put_refs(folios, NULL);
 }
 
 static inline void put_page(struct page *page)