[patch 22/23] SLUB: Slab reclaim through Lumpy reclaim

Christoph Lameter
2007-11-07T01:19:47Z

[-- Attachment #1: 0012-slab_defrag_lumpy_reclaim.patch --]
[-- Type: text/plain, Size: 7961 bytes --]

Creates a special function kmem_cache_isolate_slab() and kmem_cache_reclaim()
to support lumpy reclaim.

In order to isolate pages we will have to handle slab page allocations in
such a way that we can determine if a slab is valid whenever we access it
regardless of its time in life.

A valid slab that can be freed has PageSlab(page) and page->inuse > 0 set.
So we need to make sure in allocate_slab() that page->inuse is zero before
PageSlab is set.

kmem_cache_isolate_page() is called from lumpy reclaim to isolate pages
neighboring a page cache page that is being reclaimed. Lumpy reclaim will
gather the slabs and call kmem_cache_reclaim() on the list.

This means that we can remove a slab in order to be able to coalesce
a higher order page.

Reviewed-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Christoph Lameter <clameter@sgi.com>
---
include/linux/slab.h | 2 +
mm/slab.c | 13 ++++++
mm/slub.c | 102 ++++++++++++++++++++++++++++++++++++++++++++++++---
mm/vmscan.c | 13 +++++-
4 files changed, 123 insertions(+), 7 deletions(-)

Index: linux-2.6/include/linux/slab.h
===================================================================
--- linux-2.6.orig/include/linux/slab.h 2007-11-06 13:50:47.000000000 -0800
+++ linux-2.6/include/linux/slab.h 2007-11-06 13:50:54.000000000 -0800
@@ -64,6 +64,8 @@ unsigned int kmem_cache_size(struct kmem
const char *kmem_cache_name(struct kmem_cache *);
int kmem_ptr_validate(struct kmem_cache *cachep, const void *ptr);
int kmem_cache_defrag(int node);
+int kmem_cache_isolate_slab(struct page *);
+int kmem_cache_reclaim(struct list_head *);

/*
* Please use this macro to create slab caches. Simply specify the
Index: linux-2.6/mm/slab.c
===================================================================
--- linux-2.6.orig/mm/slab.c 2007-11-06 13:50:33.000000000 -0800
+++ linux-2.6/mm/slab.c 2007-11-06 13:50:54.000000000 -0800
@@ -2559,6 +2559,19 @@ int kmem_cache_defrag(int node)
return 0;
}

+/*
+ * SLAB does not support slab defragmentation
+ */
+int kmem_cache_isolate_slab(struct page *page)
+{
+ return -ENOSYS;
+}
+
+int kmem_cache_reclaim(struct list_head *zaplist)
+{
+ return 0;
+}
+
/**
* kmem_cache_destroy - delete a cache
* @cachep: the cache to destroy
Index: linux-2.6/mm/slub.c
===================================================================
--- linux-2.6.orig/mm/slub.c 2007-11-06 13:50:40.000000000 -0800
+++ linux-2.6/mm/slub.c 2007-11-06 13:50:54.000000000 -0800
@@ -1088,18 +1088,19 @@ static noinline struct page *new_slab(st
page = allocate_slab(s,
flags & (GFP_RECLAIM_MASK | GFP_CONSTRAINT_MASK), node);
if (!page)
- goto out;
+ return NULL;

n = get_node(s, page_to_nid(page));
if (n)
atomic_long_inc(&n->nr_slabs);
+
+ page->inuse = 0;
page->slab = s;
- state = 1 << PG_slab;
+ state = page->flags | (1 << PG_slab);
if (s->flags & (SLAB_DEBUG_FREE | SLAB_RED_ZONE | SLAB_POISON |
SLAB_STORE_USER | SLAB_TRACE))
state |= SLABDEBUG;

- page->flags |= state;
start = page_address(page);
page->end = start + 1;

@@ -1116,8 +1117,13 @@ static noinline struct page *new_slab(st
set_freepointer(s, last, page->end);

page->freelist = start;
- page->inuse = 0;
-out:
+
+ /*
+ * page->inuse must be 0 when PageSlab(page) becomes
+ * true so that defrag knows that this slab is not in use.
+ */
+ smp_wmb();
+ page->flags = state;
return page;
}

@@ -2622,6 +2628,92 @@ out:
}
#endif

+
+/*
+ * Check if the given state is that of a reclaimable slab page.
+ *
+ * This is only true if this is indeed a slab page and if
+ * the page has not been frozen.
+ */
+static inline int reclaimable_slab(unsigned long state)
+{
+ if (!(state & (1 << PG_slab)))
+ return 0;
+
+ if (state & FROZEN)
+ return 0;
+
+ return 1;
+}
+
+ /*
+ * Isolate page from the slab partial lists. Return 0 if succesful.
+ *
+ * After isolation the LRU field can be used to put the page onto
+ * a reclaim list.
+ */
+int kmem_cache_isolate_slab(struct page *page)
+{
+ unsigned long flags;
+ struct kmem_cache *s;
+ int rc = -ENOENT;
+ unsigned long state;
+
+ /*
+ * Avoid attempting to isolate the slab pages if there are
+ * indications that this will not be successful.
+ */
+ if (!reclaimable_slab(page->flags) || page_count(page) == 1)
+ return rc;
+
+ /*
+ * Get a reference to the page. Return if its freed or being freed.
+ * This is necessary to make sure that the page does not vanish
+ * from under us before we are able to check the result.
+ */
+ if (!get_page_unless_zero(page))
+ return rc;
+
+ local_irq_save(flags);
+ state = slab_lock(page);
+
+ /*
+ * Check the flags again now that we have locked it.
+ */
+ if (!reclaimable_slab(flags) || !page->inuse) {
+ slab_unlock(page, state);
+ put_page(page);
+ goto out;
+ }
+
+ /*
+ * Drop reference count. There are object remaining and therefore
+ * the slab lock will have to be taken before the last object can
+ * be removed. We hold the slab lock, so no one can free this slab
+ * now.
+ *
+ * We set the slab frozen before releasing the lock. This means
+ * that no slab free action will be performed. If all objects are
+ * removed then the slab will be freed during kmem_cache_reclaim().
+ */
+ BUG_ON(page_count(page) <= 1);
+ put_page(page);
+
+ /*
+ * Remove the slab from the lists and mark it frozen
+ */
+ s = page->slab;
+ if (page->inuse < s->objects)
+ remove_partial(s, page);
+ else if (s->flags & SLAB_STORE_USER)
+ remove_full(s, page);
+ slab_unlock(page, state | FROZEN);
+ rc = 0;
+out:
+ local_irq_restore(flags);
+ return rc;
+}
+
/*
* Conversion table for small slabs sizes / 8 to the index in the
* kmalloc array. This is necessary for slabs < 192 since we have non power
Index: linux-2.6/mm/vmscan.c
===================================================================
--- linux-2.6.orig/mm/vmscan.c 2007-11-06 13:50:47.000000000 -0800
+++ linux-2.6/mm/vmscan.c 2007-11-06 13:50:54.000000000 -0800
@@ -687,6 +687,7 @@ static int __isolate_lru_page(struct pag
*/
static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
struct list_head *src, struct list_head *dst,
+ struct list_head *slab_pages,
unsigned long *scanned, int order, int mode)
{
unsigned long nr_taken = 0;
@@ -760,7 +761,13 @@ static unsigned long isolate_lru_pages(u
case -EBUSY:
/* else it is being freed elsewhere */
list_move(&cursor_page->lru, src);
+ break;
+
default:
+ if (slab_pages &&
+ kmem_cache_isolate_slab(cursor_page) == 0)
+ list_add(&cursor_page->lru,
+ slab_pages);
break;
}
}
@@ -796,6 +803,7 @@ static unsigned long shrink_inactive_lis
struct zone *zone, struct scan_control *sc)
{
LIST_HEAD(page_list);
+ LIST_HEAD(slab_list);
struct pagevec pvec;
unsigned long nr_scanned = 0;
unsigned long nr_reclaimed = 0;
@@ -813,7 +821,7 @@ static unsigned long shrink_inactive_lis

nr_taken = isolate_lru_pages(sc->swap_cluster_max,
&zone->inactive_list,
- &page_list, &nr_scan, sc->order,
+ &page_list, &slab_list, &nr_scan, sc->order,
(sc->order > PAGE_ALLOC_COSTLY_ORDER)?
ISOLATE_BOTH : ISOLATE_INACTIVE);
nr_active = clear_active_flags(&page_list);
@@ -824,6 +832,7 @@ static unsigned long shrink_inactive_lis
-(nr_taken - nr_active));
zone->pages_scanned += nr_scan;
spin_unlock_irq(&zone->lru_lock);
+ kmem_cache_reclaim(&slab_list);

nr_scanned += nr_scan;
nr_freed = shrink_page_list(&page_list, sc, PAGEOUT_IO_ASYNC);
@@ -1029,7 +1038,7 @@ force_reclaim_mapped:
lru_add_drain();
spin_lock_irq(&zone->lru_lock);
pgmoved = isolate_lru_pages(nr_pages, &zone->active_list,
- &l_hold, &pgscanned, sc->order, ISOLATE_ACTIVE);
+ &l_hold, NULL, &pgscanned, sc->order, ISOLATE_ACTIVE);
zone->pages_scanned += pgscanned;
__mod_zone_page_state(zone, NR_ACTIVE, -pgmoved);
spin_unlock_irq(&zone->lru_lock);

--