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Subject[patch 14/19] SHM_LOCKED pages are nonreclaimable
V2 -> V3:
+ rebase to 23-mm1 atop RvR's split LRU series.
+ Use scan_mapping_noreclaim_page() on unlock. See below.

V1 -> V2:
+ modify to use reworked 'scan_all_zones_noreclaim_pages()'
See 'TODO' below - still pending.

While working with Nick Piggin's mlock patches, I noticed that
shmem segments locked via shmctl(SHM_LOCKED) were not being handled.
SHM_LOCKed pages work like ramdisk pages--the writeback function
just redirties the page so that it can't be reclaimed. Deal with
these using the same approach as for ram disk pages.

Use the AS_NORECLAIM flag to mark address_space of SHM_LOCKed
shared memory regions as non-reclaimable. Then these pages
will be culled off the normal LRU lists during vmscan.

Add new wrapper function to clear the mapping's noreclaim state
when/if shared memory segment is munlocked.

Add 'scan_mapping_noreclaim_page()' to mm/vmscan.c to scan all
pages in the shmem segment's mapping [struct address_space] for
reclaimability now that they're no longer locked. If so, move
them to the appropriate zone lru list.

Changes depend on [CONFIG_]NORECLAIM.

Signed-off-by: Lee Schermerhorn <lee.schermerhorn@hp.com>
Signed-off-by: Rik van Riel <riel@redhat.com>

Index: linux-2.6.24-rc6-mm1/mm/shmem.c
===================================================================
--- linux-2.6.24-rc6-mm1.orig/mm/shmem.c 2008-01-08 12:08:02.000000000 -0500
+++ linux-2.6.24-rc6-mm1/mm/shmem.c 2008-01-08 12:17:25.000000000 -0500
@@ -1468,10 +1468,13 @@ int shmem_lock(struct file *file, int lo
if (!user_shm_lock(inode->i_size, user))
goto out_nomem;
info->flags |= VM_LOCKED;
+ mapping_set_noreclaim(file->f_mapping);
}
if (!lock && (info->flags & VM_LOCKED) && user) {
user_shm_unlock(inode->i_size, user);
info->flags &= ~VM_LOCKED;
+ mapping_clear_noreclaim(file->f_mapping);
+ scan_mapping_noreclaim_pages(file->f_mapping);
}
retval = 0;
out_nomem:
Index: linux-2.6.24-rc6-mm1/include/linux/pagemap.h
===================================================================
--- linux-2.6.24-rc6-mm1.orig/include/linux/pagemap.h 2008-01-08 12:17:21.000000000 -0500
+++ linux-2.6.24-rc6-mm1/include/linux/pagemap.h 2008-01-08 12:17:25.000000000 -0500
@@ -38,14 +38,20 @@ static inline void mapping_set_noreclaim
set_bit(AS_NORECLAIM, &mapping->flags);
}

+static inline void mapping_clear_noreclaim(struct address_space *mapping)
+{
+ clear_bit(AS_NORECLAIM, &mapping->flags);
+}
+
static inline int mapping_non_reclaimable(struct address_space *mapping)
{
- if (mapping && (mapping->flags & AS_NORECLAIM))
- return 1;
+ if (mapping)
+ return test_bit(AS_NORECLAIM, &mapping->flags);
return 0;
}
#else
static inline void mapping_set_noreclaim(struct address_space *mapping) { }
+static inline void mapping_clear_noreclaim(struct address_space *mapping) { }
static inline int mapping_non_reclaimable(struct address_space *mapping)
{
return 0;
Index: linux-2.6.24-rc6-mm1/mm/vmscan.c
===================================================================
--- linux-2.6.24-rc6-mm1.orig/mm/vmscan.c 2008-01-08 12:17:21.000000000 -0500
+++ linux-2.6.24-rc6-mm1/mm/vmscan.c 2008-01-08 12:17:25.000000000 -0500
@@ -2276,6 +2276,30 @@ int page_reclaimable(struct page *page,
return 1;
}

+/*
+ * check_move_noreclaim_page() -- check @page for reclaimability and move
+ * to appropriate @zone lru list.
+ * @zone->lru_lock held on entry/exit.
+ * @page is on LRU and has PageNoreclaim true
+ */
+static void check_move_noreclaim_page(struct page *page, struct zone* zone)
+{
+
+ ClearPageNoreclaim(page); /* for page_reclaimable() */
+ if(page_reclaimable(page, NULL)) {
+ enum lru_list l = LRU_INACTIVE_ANON + page_file_cache(page);
+ __dec_zone_state(zone, NR_NORECLAIM);
+ list_move(&page->lru, &zone->list[l]);
+ __inc_zone_state(zone, NR_INACTIVE_ANON + l);
+ } else {
+ /*
+ * rotate noreclaim list
+ */
+ SetPageNoreclaim(page);
+ list_move(&page->lru, &zone->list[LRU_NORECLAIM]);
+ }
+}
+
/**
* scan_zone_noreclaim_pages(@zone)
* @zone - zone to scan
@@ -2290,8 +2314,6 @@ int page_reclaimable(struct page *page,
void scan_zone_noreclaim_pages(struct zone *zone)
{
struct list_head *l_noreclaim = &zone->list[LRU_NORECLAIM];
- struct list_head *l_inactive_anon = &zone->list[LRU_INACTIVE_ANON];
- struct list_head *l_inactive_file = &zone->list[LRU_INACTIVE_FILE];
unsigned long scan;
unsigned long nr_to_scan = zone_page_state(zone, NR_NORECLAIM);

@@ -2303,26 +2325,15 @@ void scan_zone_noreclaim_pages(struct zo
for (scan = 0; scan < batch_size; scan++) {
struct page* page = lru_to_page(l_noreclaim);

- if (unlikely(!PageLRU(page) || !PageNoreclaim(page)))
+ if (TestSetPageLocked(page))
continue;

prefetchw_prev_lru_page(page, l_noreclaim, flags);

- ClearPageNoreclaim(page); /* for page_reclaimable() */
- if(page_reclaimable(page, NULL)) {
- __dec_zone_state(zone, NR_NORECLAIM);
- if (page_file_cache(page)) {
- list_move(&page->lru, l_inactive_file);
- __inc_zone_state(zone, NR_INACTIVE_FILE);
- } else {
- list_move(&page->lru, l_inactive_anon);
- __inc_zone_state(zone, NR_INACTIVE_ANON);
- }
- } else {
- SetPageNoreclaim(page);
- list_move(&page->lru, l_noreclaim);
- }
+ if (likely(PageLRU(page) && PageNoreclaim(page)))
+ check_move_noreclaim_page(page, zone);

+ unlock_page(page);
}
spin_unlock_irq(&zone->lru_lock);

@@ -2352,6 +2363,62 @@ void scan_all_zones_noreclaim_pages(void
}
}

+/**
+ * scan_mapping_noreclaim_pages(mapping)
+ * @mapping - struct address_space to scan for reclaimable pages
+ *
+ * scan all pages in mapping. check non-reclaimable pages for
+ * reclaimabililty and move them to the appropriate zone lru list.
+ */
+void scan_mapping_noreclaim_pages(struct address_space *mapping)
+{
+ pgoff_t next = 0;
+ pgoff_t end = i_size_read(mapping->host);
+ struct zone *zone;
+ struct pagevec pvec;
+
+ if (mapping->nrpages == 0)
+ return;
+
+ pagevec_init(&pvec, 0);
+ while (next < end &&
+ pagevec_lookup(&pvec, mapping, next, PAGEVEC_SIZE)) {
+ int i;
+
+ zone = NULL;
+
+ for (i = 0; i < pagevec_count(&pvec); i++) {
+ struct page *page = pvec.pages[i];
+ pgoff_t page_index = page->index;
+ struct zone *pagezone = page_zone(page);
+
+ if (page_index > next)
+ next = page_index;
+ next++;
+
+ if (TestSetPageLocked(page))
+ continue;
+
+ if (pagezone != zone) {
+ if (zone)
+ spin_unlock(&zone->lru_lock);
+ zone = pagezone;
+ spin_lock(&zone->lru_lock);
+ }
+
+ if (PageLRU(page) && PageNoreclaim(page))
+ check_move_noreclaim_page(page, zone);
+
+ unlock_page(page);
+
+ }
+ if (zone)
+ spin_unlock(&zone->lru_lock);
+ pagevec_release(&pvec);
+ }
+
+}
+
/*
* scan_noreclaim_pages [vm] sysctl handler. On demand re-scan of
* all nodes' noreclaim lists for reclaimable pages
Index: linux-2.6.24-rc6-mm1/include/linux/swap.h
===================================================================
--- linux-2.6.24-rc6-mm1.orig/include/linux/swap.h 2008-01-08 12:17:17.000000000 -0500
+++ linux-2.6.24-rc6-mm1/include/linux/swap.h 2008-01-08 12:17:25.000000000 -0500
@@ -218,6 +218,7 @@ static inline int zone_reclaim(struct zo
extern int page_reclaimable(struct page *page, struct vm_area_struct *vma);
extern void scan_zone_noreclaim_pages(struct zone *);
extern void scan_all_zones_noreclaim_pages(void);
+extern void scan_mapping_noreclaim_pages(struct address_space *);
extern unsigned long scan_noreclaim_pages;
extern int scan_noreclaim_handler(struct ctl_table *, int, struct file *,
void __user *, size_t *, loff_t *);
@@ -231,6 +232,9 @@ static inline int page_reclaimable(struc
}
static inline void scan_zone_noreclaim_pages(struct zone *z) { }
static inline void scan_all_zones_noreclaim_pages(void) { }
+static inline void scan_mapping_noreclaim_pages(struct address_space *mapping)
+{
+}
static inline int scan_noreclaim_register_node(struct node *node)
{
return 0;
--
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