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From: Mel Gorman on 15 Apr 2010 13:30
shrink_page_list() sets up a pagevec to release pages as according as they
are free. It uses significant amounts of stack on the pagevec. This
patch adds pages to be freed via pagevec to a linked list which is then
freed en-masse at the end. This avoids using stack in the main path that
potentially calls writepage().

Signed-off-by: Mel Gorman <mel(a)csn.ul.ie>
---
mm/vmscan.c | 34 ++++++++++++++++++++++++++--------
1 files changed, 26 insertions(+), 8 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 9bc1ede..2c22c83 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -619,6 +619,22 @@ static enum page_references page_check_references(struct page *page,
return PAGEREF_RECLAIM;
}

+static void free_page_list(struct list_head *free_list)
+{
+ struct pagevec freed_pvec;
+ struct page *page, *tmp;
+
+ pagevec_init(&freed_pvec, 1);
+
+ list_for_each_entry_safe(page, tmp, free_list, lru) {
+ list_del(&page->lru);
+ if (!pagevec_add(&freed_pvec, page)) {
+ __pagevec_free(&freed_pvec);
+ pagevec_reinit(&freed_pvec);
+ }
+ }
+}
+
/*
* shrink_page_list() returns the number of reclaimed pages
*/
@@ -627,13 +643,12 @@ static unsigned long shrink_page_list(struct list_head *page_list,
enum pageout_io sync_writeback)
{
LIST_HEAD(ret_pages);
- struct pagevec freed_pvec;
+ LIST_HEAD(free_list);
int pgactivate = 0;
unsigned long nr_reclaimed = 0;

cond_resched();

- pagevec_init(&freed_pvec, 1);
while (!list_empty(page_list)) {
enum page_references references;
struct address_space *mapping;
@@ -808,10 +823,12 @@ static unsigned long shrink_page_list(struct list_head *page_list,
__clear_page_locked(page);
free_it:
nr_reclaimed++;
- if (!pagevec_add(&freed_pvec, page)) {
- __pagevec_free(&freed_pvec);
- pagevec_reinit(&freed_pvec);
- }
+
+ /*
+ * Is there need to periodically free_page_list? It would
+ * appear not as the counts should be low
+ */
+ list_add(&page->lru, &free_list);
continue;

cull_mlocked:
@@ -834,9 +851,10 @@ keep:
list_add(&page->lru, &ret_pages);
VM_BUG_ON(PageLRU(page) || PageUnevictable(page));
}
+
+ free_page_list(&free_list);
+
list_splice(&ret_pages, page_list);
- if (pagevec_count(&freed_pvec))
- __pagevec_free(&freed_pvec);
count_vm_events(PGACTIVATE, pgactivate);
return nr_reclaimed;
}
--
1.6.5

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Prev: [PATCH 06/10] vmscan: Split shrink_zone to reduce stack usage
Next: [PATCH 07/10] vmscan: Remove unnecessary temporary variables in shrink_zone()