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Subject[PATCH -mm 04/25] free swap space on swap-in/activation
From: Rik van Riel <riel@redhat.com>

Free swap cache entries when swapping in pages if vm_swap_full()
[swap space > 1/2 used]. Uses new pagevec to reduce pressure
on locks.
Signed-off-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Lee Schermerhorn <Lee.Schermerhorn@hp.com>
Signed-off-by: MinChan Kim <minchan.kim@gmail.com>

---
include/linux/pagevec.h | 1 +
include/linux/swap.h | 6 ++++++
mm/swap.c | 18 ++++++++++++++++++
mm/swapfile.c | 25 ++++++++++++++++++++++---
mm/vmscan.c | 7 +++++++
5 files changed, 54 insertions(+), 3 deletions(-)
Index: linux-2.6.26-rc2-mm1/mm/vmscan.c
===================================================================
--- linux-2.6.26-rc2-mm1.orig/mm/vmscan.c 2008-05-23 14:21:33.000000000 -0400
+++ linux-2.6.26-rc2-mm1/mm/vmscan.c 2008-05-23 14:21:33.000000000 -0400
@@ -619,6 +619,9 @@ free_it:
continue;

activate_locked:
+ /* Not a candidate for swapping, so reclaim swap space. */
+ if (PageSwapCache(page) && vm_swap_full())
+ remove_exclusive_swap_page_ref(page);
SetPageActive(page);
pgactivate++;
keep_locked:
@@ -1203,6 +1206,8 @@ static void shrink_active_list(unsigned
__mod_zone_page_state(zone, NR_ACTIVE, pgmoved);
pgmoved = 0;
spin_unlock_irq(&zone->lru_lock);
+ if (vm_swap_full())
+ pagevec_swap_free(&pvec);
__pagevec_release(&pvec);
spin_lock_irq(&zone->lru_lock);
}
@@ -1212,6 +1217,8 @@ static void shrink_active_list(unsigned
__count_zone_vm_events(PGREFILL, zone, pgscanned);
__count_vm_events(PGDEACTIVATE, pgdeactivate);
spin_unlock_irq(&zone->lru_lock);
+ if (vm_swap_full())
+ pagevec_swap_free(&pvec);

pagevec_release(&pvec);
}
Index: linux-2.6.26-rc2-mm1/mm/swap.c
===================================================================
--- linux-2.6.26-rc2-mm1.orig/mm/swap.c 2008-05-23 14:21:33.000000000 -0400
+++ linux-2.6.26-rc2-mm1/mm/swap.c 2008-05-23 14:21:33.000000000 -0400
@@ -443,6 +443,24 @@ void pagevec_strip(struct pagevec *pvec)
}
}

+/*
+ * Try to free swap space from the pages in a pagevec
+ */
+void pagevec_swap_free(struct pagevec *pvec)
+{
+ int i;
+
+ for (i = 0; i < pagevec_count(pvec); i++) {
+ struct page *page = pvec->pages[i];
+
+ if (PageSwapCache(page) && !TestSetPageLocked(page)) {
+ if (PageSwapCache(page))
+ remove_exclusive_swap_page_ref(page);
+ unlock_page(page);
+ }
+ }
+}
+
/**
* pagevec_lookup - gang pagecache lookup
* @pvec: Where the resulting pages are placed
Index: linux-2.6.26-rc2-mm1/include/linux/pagevec.h
===================================================================
--- linux-2.6.26-rc2-mm1.orig/include/linux/pagevec.h 2008-05-23 14:21:33.000000000 -0400
+++ linux-2.6.26-rc2-mm1/include/linux/pagevec.h 2008-05-23 14:21:33.000000000 -0400
@@ -25,6 +25,7 @@ void __pagevec_release_nonlru(struct pag
void __pagevec_free(struct pagevec *pvec);
void ____pagevec_lru_add(struct pagevec *pvec, enum lru_list lru);
void pagevec_strip(struct pagevec *pvec);
+void pagevec_swap_free(struct pagevec *pvec);
unsigned pagevec_lookup(struct pagevec *pvec, struct address_space *mapping,
pgoff_t start, unsigned nr_pages);
unsigned pagevec_lookup_tag(struct pagevec *pvec,
Index: linux-2.6.26-rc2-mm1/include/linux/swap.h
===================================================================
--- linux-2.6.26-rc2-mm1.orig/include/linux/swap.h 2008-05-23 14:21:33.000000000 -0400
+++ linux-2.6.26-rc2-mm1/include/linux/swap.h 2008-05-23 14:21:33.000000000 -0400
@@ -265,6 +265,7 @@ extern sector_t swapdev_block(int, pgoff
extern struct swap_info_struct *get_swap_info_struct(unsigned);
extern int can_share_swap_page(struct page *);
extern int remove_exclusive_swap_page(struct page *);
+extern int remove_exclusive_swap_page_ref(struct page *);
struct backing_dev_info;

/* linux/mm/thrash.c */
@@ -353,6 +354,11 @@ static inline int remove_exclusive_swap_
return 0;
}

+static inline int remove_exclusive_swap_page_ref(struct page *page)
+{
+ return 0;
+}
+
static inline swp_entry_t get_swap_page(void)
{
swp_entry_t entry;
Index: linux-2.6.26-rc2-mm1/mm/swapfile.c
===================================================================
--- linux-2.6.26-rc2-mm1.orig/mm/swapfile.c 2008-05-23 14:21:21.000000000 -0400
+++ linux-2.6.26-rc2-mm1/mm/swapfile.c 2008-05-23 14:21:33.000000000 -0400
@@ -343,7 +343,7 @@ int can_share_swap_page(struct page *pag
* Work out if there are any other processes sharing this
* swap cache page. Free it if you can. Return success.
*/
-int remove_exclusive_swap_page(struct page *page)
+static int remove_exclusive_swap_page_count(struct page *page, int count)
{
int retval;
struct swap_info_struct * p;
@@ -356,7 +356,7 @@ int remove_exclusive_swap_page(struct pa
return 0;
if (PageWriteback(page))
return 0;
- if (page_count(page) != 2) /* 2: us + cache */
+ if (page_count(page) != count) /* us + cache + ptes */
return 0;

entry.val = page_private(page);
@@ -369,7 +369,7 @@ int remove_exclusive_swap_page(struct pa
if (p->swap_map[swp_offset(entry)] == 1) {
/* Recheck the page count with the swapcache lock held.. */
write_lock_irq(&swapper_space.tree_lock);
- if ((page_count(page) == 2) && !PageWriteback(page)) {
+ if ((page_count(page) == count) && !PageWriteback(page)) {
__delete_from_swap_cache(page);
SetPageDirty(page);
retval = 1;
@@ -387,6 +387,25 @@ int remove_exclusive_swap_page(struct pa
}

/*
+ * Most of the time the page should have two references: one for the
+ * process and one for the swap cache.
+ */
+int remove_exclusive_swap_page(struct page *page)
+{
+ return remove_exclusive_swap_page_count(page, 2);
+}
+
+/*
+ * The pageout code holds an extra reference to the page. That raises
+ * the reference count to test for to 2 for a page that is only in the
+ * swap cache plus 1 for each process that maps the page.
+ */
+int remove_exclusive_swap_page_ref(struct page *page)
+{
+ return remove_exclusive_swap_page_count(page, 2 + page_mapcount(page));
+}
+
+/*
* Free the swap entry like above, but also try to
* free the page cache entry if it is the last user.
*/
--
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