[PATCH] temporarily disable swap token on memory pressure

Some users (hi Zwane) have seen a problem when running a workload that
eats nearly all of physical memory - th system does an OOM kill, even
when there is still a lot of swap free.

The problem appears to be a very big task that is holding the swap
token, and the VM has a very hard time finding any other page in the
system that is swappable.

Instead of ignoring the swap token when sc->priority reaches 0, we could
simply take the swap token away from the memory hog and make sure we
don't give it back to the memory hog for a few seconds.

This patch resolves the problem Zwane ran into.

Signed-off-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

3 files changed, 26 insertions, 21 deletions

diff --git a/mm/rmap.c b/mm/rmap.c
index 6389cda02a2..491ac350048 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -290,7 +290,7 @@ pte_t *page_check_address(struct page *page, struct mm_struct *mm,
  * repeatedly from either page_referenced_anon or page_referenced_file.
  */
 static int page_referenced_one(struct page *page,
-        struct vm_area_struct *vma, unsigned int *mapcount, int ignore_token)
+        struct vm_area_struct *vma, unsigned int *mapcount)
 {
         struct mm_struct *mm = vma->vm_mm;
         unsigned long address;
@@ -311,7 +311,7 @@ static int page_referenced_one(struct page *page,
 
         /* Pretend the page is referenced if the task has the
            swap token and is in the middle of a page fault. */
-        if (mm != current->mm && !ignore_token && has_swap_token(mm) &&
+        if (mm != current->mm && has_swap_token(mm) &&
                         rwsem_is_locked(&mm->mmap_sem))
                 referenced++;
 
@@ -321,7 +321,7 @@ out:
         return referenced;
 }
 
-static int page_referenced_anon(struct page *page, int ignore_token)
+static int page_referenced_anon(struct page *page)
 {
         unsigned int mapcount;
         struct anon_vma *anon_vma;
@@ -334,8 +334,7 @@ static int page_referenced_anon(struct page *page, int ignore_token)
 
         mapcount = page_mapcount(page);
         list_for_each_entry(vma, &anon_vma->head, anon_vma_node) {
-                referenced += page_referenced_one(page, vma, &mapcount,
-                                                        ignore_token);
+                referenced += page_referenced_one(page, vma, &mapcount);
                 if (!mapcount)
                         break;
         }
@@ -354,7 +353,7 @@ static int page_referenced_anon(struct page *page, int ignore_token)
  *
  * This function is only called from page_referenced for object-based pages.
  */
-static int page_referenced_file(struct page *page, int ignore_token)
+static int page_referenced_file(struct page *page)
 {
         unsigned int mapcount;
         struct address_space *mapping = page->mapping;
@@ -392,8 +391,7 @@ static int page_referenced_file(struct page *page, int ignore_token)
                         referenced++;
                         break;
                 }
-                referenced += page_referenced_one(page, vma, &mapcount,
-                                                        ignore_token);
+                referenced += page_referenced_one(page, vma, &mapcount);
                 if (!mapcount)
                         break;
         }
@@ -410,13 +408,10 @@ static int page_referenced_file(struct page *page, int ignore_token)
  * Quick test_and_clear_referenced for all mappings to a page,
  * returns the number of ptes which referenced the page.
  */
-int page_referenced(struct page *page, int is_locked, int ignore_token)
+int page_referenced(struct page *page, int is_locked)
 {
         int referenced = 0;
 
-        if (!swap_token_default_timeout)
-                ignore_token = 1;
-
         if (page_test_and_clear_young(page))
                 referenced++;
 
@@ -425,15 +420,14 @@ int page_referenced(struct page *page, int is_locked, int ignore_token)
 
         if (page_mapped(page) && page->mapping) {
                 if (PageAnon(page))
-                        referenced += page_referenced_anon(page, ignore_token);
+                        referenced += page_referenced_anon(page);
                 else if (is_locked)
-                        referenced += page_referenced_file(page, ignore_token);
+                        referenced += page_referenced_file(page);
                 else if (TestSetPageLocked(page))
                         referenced++;
                 else {
                         if (page->mapping)
-                                referenced += page_referenced_file(page,
-                                                                ignore_token);
+                                referenced += page_referenced_file(page);
                         unlock_page(page);
                 }
         }
diff --git a/mm/thrash.c b/mm/thrash.c
index eff3c18c33a..f4c560b4a2b 100644
--- a/mm/thrash.c
+++ b/mm/thrash.c
@@ -57,14 +57,17 @@ void grab_swap_token(void)
         /* We have the token. Let others know we still need it. */
         if (has_swap_token(current->mm)) {
                 current->mm->recent_pagein = 1;
+                if (unlikely(!swap_token_default_timeout))
+                        disable_swap_token();
                 return;
         }
 
         if (time_after(jiffies, swap_token_check)) {
 
-                /* Can't get swapout protection if we exceed our RSS limit. */
-                // if (current->mm->rss > current->mm->rlimit_rss)
-                //      return;
+                if (!swap_token_default_timeout) {
+                        swap_token_check = jiffies + SWAP_TOKEN_CHECK_INTERVAL;
+                        return;
+                }
 
                 /* ... or if we recently held the token. */
                 if (time_before(jiffies, current->mm->swap_token_time))
@@ -95,6 +98,7 @@ void __put_swap_token(struct mm_struct *mm)
 {
         spin_lock(&swap_token_lock);
         if (likely(mm == swap_token_mm)) {
+                mm->swap_token_time = jiffies + SWAP_TOKEN_CHECK_INTERVAL;
                 swap_token_mm = &init_mm;
                 swap_token_check = jiffies;
         }
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 28130541270..078cf920208 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -407,7 +407,7 @@ static int shrink_list(struct list_head *page_list, struct scan_control *sc)
                 if (PageWriteback(page))
                         goto keep_locked;
 
-                referenced = page_referenced(page, 1, sc->priority <= 0);
+                referenced = page_referenced(page, 1);
                 /* In active use or really unfreeable?  Activate it. */
                 if (referenced && page_mapping_inuse(page))
                         goto activate_locked;
@@ -756,7 +756,7 @@ refill_inactive_zone(struct zone *zone, struct scan_control *sc)
                 if (page_mapped(page)) {
                         if (!reclaim_mapped ||
                             (total_swap_pages == 0 && PageAnon(page)) ||
-                            page_referenced(page, 0, sc->priority <= 0)) {
+                            page_referenced(page, 0)) {
                                 list_add(&page->lru, &l_active);
                                 continue;
                         }
@@ -960,6 +960,8 @@ int try_to_free_pages(struct zone **zones, gfp_t gfp_mask)
                 sc.nr_reclaimed = 0;
                 sc.priority = priority;
                 sc.swap_cluster_max = SWAP_CLUSTER_MAX;
+                if (!priority)
+                        disable_swap_token();
                 shrink_caches(zones, &sc);
                 shrink_slab(sc.nr_scanned, gfp_mask, lru_pages);
                 if (reclaim_state) {
@@ -1056,6 +1058,10 @@ loop_again:
                 int end_zone = 0;       /* Inclusive.  0 = ZONE_DMA */
                 unsigned long lru_pages = 0;
 
+                /* The swap token gets in the way of swapout... */
+                if (!priority)
+                        disable_swap_token();
+
                 all_zones_ok = 1;
 
                 if (nr_pages == 0) {
@@ -1360,6 +1366,7 @@ int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
         sc.nr_reclaimed = 0;
         /* scan at the highest priority */
         sc.priority = 0;
+        disable_swap_token();
 
         if (nr_pages > SWAP_CLUSTER_MAX)
                 sc.swap_cluster_max = nr_pages;