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Subject[patch 14/14] SHM_LOCKED pages are nonreclaimable
From: Lee Schermerhorn <Lee.Schermerhorn@hp.com>

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_LRU.

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

---
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.

include/linux/pagemap.h | 10 ++++-
include/linux/swap.h | 4 ++
mm/shmem.c | 3 +
mm/vmscan.c | 85 ++++++++++++++++++++++++++++++++++++++++++++++++
4 files changed, 100 insertions(+), 2 deletions(-)

Index: linux-2.6.26-rc2-mm1/mm/shmem.c
===================================================================
--- linux-2.6.26-rc2-mm1.orig/mm/shmem.c 2008-05-16 13:31:54.000000000 -0400
+++ linux-2.6.26-rc2-mm1/mm/shmem.c 2008-05-16 14:05:23.000000000 -0400
@@ -1469,10 +1469,13 @@ 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-2.6.26-rc2-mm1/include/linux/pagemap.h
===================================================================
--- linux-2.6.26-rc2-mm1.orig/include/linux/pagemap.h 2008-05-16 14:05:19.000000000 -0400
+++ linux-2.6.26-rc2-mm1/include/linux/pagemap.h 2008-05-16 14:05:23.000000000 -0400
@@ -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-2.6.26-rc2-mm1/mm/vmscan.c
===================================================================
--- linux-2.6.26-rc2-mm1.orig/mm/vmscan.c 2008-05-16 14:05:19.000000000 -0400
+++ linux-2.6.26-rc2-mm1/mm/vmscan.c 2008-05-16 14:05:23.000000000 -0400
@@ -2274,4 +2274,89 @@ int page_reclaimable(struct page *page,

return 1;
}
+
+/**
+ * check_move_noreclaim_page - check page for reclaimability and move to appropriate zone lru list
+ * @page: page to check reclaimability and move to appropriate lru list
+ * @zone: zone page is in
+ *
+ * Checks a page for reclaimability and moves the page to the appropriate
+ * zone lru list.
+ *
+ * Restrictions: zone->lru_lock must be held, page must be on LRU and must
+ * have PageNoreclaim set.
+ */
+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_mapping_noreclaim_pages - scan an address space for reclaimable pages
+ * @mapping: struct address_space to scan for reclaimable pages
+ *
+ * Scan all pages in mapping. Check non-reclaimable pages for
+ * reclaimability 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);
+ }
+
+}
#endif
Index: linux-2.6.26-rc2-mm1/include/linux/swap.h
===================================================================
--- linux-2.6.26-rc2-mm1.orig/include/linux/swap.h 2008-05-16 14:05:09.000000000 -0400
+++ linux-2.6.26-rc2-mm1/include/linux/swap.h 2008-05-16 14:05:23.000000000 -0400
@@ -242,12 +242,16 @@ static inline int zone_reclaim(struct zo

#ifdef CONFIG_NORECLAIM_LRU
extern int page_reclaimable(struct page *page, struct vm_area_struct *vma);
+extern void scan_mapping_noreclaim_pages(struct address_space *);
#else
static inline int page_reclaimable(struct page *page,
struct vm_area_struct *vma)
{
return 1;
}
+static inline void scan_mapping_noreclaim_pages(struct address_space *mapping)
+{
+}
#endif

extern int kswapd_run(int nid);
--
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