Andrew Morton wrote:

On Fri, 29 Jul 2011 11:58:37 +0400
Konstantin Khlebnikov[off-list ref]  wrote:

quoted

This patch adds helper free_hot_cold_page_list() to free list of 0-order pages.
It frees pages directly from list without temporary page-vector.
It also calls trace_mm_pagevec_free() to simulate pagevec_free() behaviour.

bloat-o-meter:

add/remove: 1/1 grow/shrink: 1/3 up/down: 267/-295 (-28)
function                                     old     new   delta
free_hot_cold_page_list                        -     264    +264
get_page_from_freelist                      2129    2132      +3
__pagevec_free                               243     239      -4
split_free_page                              380     373      -7
release_pages                                606     510     -96
free_page_list                               188       -    -188

It saves a total of 150 bytes for me.

quoted

index cb40892..dd7b9cc 100644

--- a/include/linux/gfp.h
+++ b/include/linux/gfp.h

@@ -358,6 +358,7 @@ void *alloc_pages_exact_nid(int nid, size_t size, gfp_t gfp_mask);
  extern void __free_pages(struct page *page, unsigned int order);
  extern void free_pages(unsigned long addr, unsigned int order);
  extern void free_hot_cold_page(struct page *page, int cold);
+extern void free_hot_cold_page_list(struct list_head *list, int cold);

  #define __free_page(page) __free_pages((page), 0)
  #define free_page(addr) free_pages((addr), 0)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 1dbcf88..af486e4 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c

@@ -1209,6 +1209,18 @@ out:
  	local_irq_restore(flags);
  }

+void free_hot_cold_page_list(struct list_head *list, int cold)
+{
+	struct page *page, *next;
+
+	list_for_each_entry_safe(page, next, list, lru) {
+		trace_mm_pagevec_free(page, cold);
+		free_hot_cold_page(page, cold);
+	}
+
+	INIT_LIST_HEAD(list);
+}
+
  /*
   * split_page takes a non-compound higher-order page, and splits it into
   * n (1<<order) sub-pages: page[0..n]

diff --git a/mm/swap.c b/mm/swap.c
index 3a442f1..b9138c7 100644
--- a/mm/swap.c
+++ b/mm/swap.c

@@ -562,11 +562,10 @@ int lru_add_drain_all(void)
  void release_pages(struct page **pages, int nr, int cold)
  {
  	int i;
-	struct pagevec pages_to_free;
+	LIST_HEAD(pages_to_free);
  	struct zone *zone = NULL;
  	unsigned long uninitialized_var(flags);

-	pagevec_init(&pages_to_free, cold);
  	for (i = 0; i<  nr; i++) {
  		struct page *page = pages[i];

@@ -597,19 +596,12 @@ void release_pages(struct page **pages, int nr, int cold)
  			del_page_from_lru(zone, page);
  		}

-		if (!pagevec_add(&pages_to_free, page)) {
-			if (zone) {
-				spin_unlock_irqrestore(&zone->lru_lock, flags);
-				zone = NULL;
-			}
-			__pagevec_free(&pages_to_free);
-			pagevec_reinit(&pages_to_free);
-  		}
+		list_add_tail(&page->lru,&pages_to_free);

There's a potential problem here with cache longevity.  If
release_pages() is called with a large number of pages then the current
code's approach of freeing pages 16-at-a-time will hopefully cause
those pageframes to still be in CPU cache when we get to actually
freeing them.

But after this change, we free all the pages in a single operation
right at the end, which adds risk that we'll have to reload all their
pageframes into CPU cache again.

That'll only be a problem if release_pages() _is_ called with a large
number of pages.  And manipulating large numbers of pages represents a
lot of work, so the additional work from one cachemiss per page will
presumably be tiny.

all release_pages() callers (except fuse) call it for pages array not bigger than PAGEVEC_SIZE (=14).
while for fuse it put likely not last page reference, so we didn't free them on this path.

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