mm: new shrinker API
The current shrinker callout API uses an a single shrinker call for
multiple functions. To determine the function, a special magical value is
passed in a parameter to change the behaviour. This complicates the
implementation and return value specification for the different
behaviours.
Separate the two different behaviours into separate operations, one to
return a count of freeable objects in the cache, and another to scan a
certain number of objects in the cache for freeing. In defining these new
operations, ensure the return values and resultant behaviours are clearly
defined and documented.
Modify shrink_slab() to use the new API and implement the callouts for all
the existing shrinkers.
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Glauber Costa <glommer@parallels.com>
Acked-by: Mel Gorman <mgorman@suse.de>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Cc: Arve Hjønnevåg <arve@android.com>
Cc: Carlos Maiolino <cmaiolino@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Chuck Lever <chuck.lever@oracle.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: David Rientjes <rientjes@google.com>
Cc: Gleb Natapov <gleb@redhat.com>
Cc: Greg Thelen <gthelen@google.com>
Cc: J. Bruce Fields <bfields@redhat.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: John Stultz <john.stultz@linaro.org>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Kent Overstreet <koverstreet@google.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Steven Whitehouse <swhiteho@redhat.com>
Cc: Thomas Hellstrom <thellstrom@vmware.com>
Cc: Trond Myklebust <Trond.Myklebust@netapp.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h
index ac6b8ee..884e762 100644
--- a/include/linux/shrinker.h
+++ b/include/linux/shrinker.h
@@ -4,6 +4,12 @@
/*
* This struct is used to pass information from page reclaim to the shrinkers.
* We consolidate the values for easier extention later.
+ *
+ * The 'gfpmask' refers to the allocation we are currently trying to
+ * fulfil.
+ *
+ * Note that 'shrink' will be passed nr_to_scan == 0 when the VM is
+ * querying the cache size, so a fastpath for that case is appropriate.
*/
struct shrink_control {
gfp_t gfp_mask;
@@ -12,23 +18,37 @@
unsigned long nr_to_scan;
};
+#define SHRINK_STOP (~0UL)
/*
* A callback you can register to apply pressure to ageable caches.
*
- * 'sc' is passed shrink_control which includes a count 'nr_to_scan'
- * and a 'gfpmask'. It should look through the least-recently-used
- * 'nr_to_scan' entries and attempt to free them up. It should return
- * the number of objects which remain in the cache. If it returns -1, it means
- * it cannot do any scanning at this time (eg. there is a risk of deadlock).
+ * @shrink() should look through the least-recently-used 'nr_to_scan' entries
+ * and attempt to free them up. It should return the number of objects which
+ * remain in the cache. If it returns -1, it means it cannot do any scanning at
+ * this time (eg. there is a risk of deadlock).
*
- * The 'gfpmask' refers to the allocation we are currently trying to
- * fulfil.
+ * @count_objects should return the number of freeable items in the cache. If
+ * there are no objects to free or the number of freeable items cannot be
+ * determined, it should return 0. No deadlock checks should be done during the
+ * count callback - the shrinker relies on aggregating scan counts that couldn't
+ * be executed due to potential deadlocks to be run at a later call when the
+ * deadlock condition is no longer pending.
*
- * Note that 'shrink' will be passed nr_to_scan == 0 when the VM is
- * querying the cache size, so a fastpath for that case is appropriate.
+ * @scan_objects will only be called if @count_objects returned a non-zero
+ * value for the number of freeable objects. The callout should scan the cache
+ * and attempt to free items from the cache. It should then return the number
+ * of objects freed during the scan, or SHRINK_STOP if progress cannot be made
+ * due to potential deadlocks. If SHRINK_STOP is returned, then no further
+ * attempts to call the @scan_objects will be made from the current reclaim
+ * context.
*/
struct shrinker {
int (*shrink)(struct shrinker *, struct shrink_control *sc);
+ unsigned long (*count_objects)(struct shrinker *,
+ struct shrink_control *sc);
+ unsigned long (*scan_objects)(struct shrinker *,
+ struct shrink_control *sc);
+
int seeks; /* seeks to recreate an obj */
long batch; /* reclaim batch size, 0 = default */
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 2cff0d4..4d4e859 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -205,19 +205,24 @@
*
* Returns the number of slab objects which we shrunk.
*/
-unsigned long shrink_slab(struct shrink_control *shrink,
+unsigned long shrink_slab(struct shrink_control *shrinkctl,
unsigned long nr_pages_scanned,
unsigned long lru_pages)
{
struct shrinker *shrinker;
- unsigned long ret = 0;
+ unsigned long freed = 0;
if (nr_pages_scanned == 0)
nr_pages_scanned = SWAP_CLUSTER_MAX;
if (!down_read_trylock(&shrinker_rwsem)) {
- /* Assume we'll be able to shrink next time */
- ret = 1;
+ /*
+ * If we would return 0, our callers would understand that we
+ * have nothing else to shrink and give up trying. By returning
+ * 1 we keep it going and assume we'll be able to shrink next
+ * time.
+ */
+ freed = 1;
goto out;
}
@@ -225,14 +230,16 @@
unsigned long long delta;
long total_scan;
long max_pass;
- int shrink_ret = 0;
long nr;
long new_nr;
long batch_size = shrinker->batch ? shrinker->batch
: SHRINK_BATCH;
- max_pass = do_shrinker_shrink(shrinker, shrink, 0);
- if (max_pass <= 0)
+ if (shrinker->count_objects)
+ max_pass = shrinker->count_objects(shrinker, shrinkctl);
+ else
+ max_pass = do_shrinker_shrink(shrinker, shrinkctl, 0);
+ if (max_pass == 0)
continue;
/*
@@ -248,8 +255,8 @@
do_div(delta, lru_pages + 1);
total_scan += delta;
if (total_scan < 0) {
- printk(KERN_ERR "shrink_slab: %pF negative objects to "
- "delete nr=%ld\n",
+ printk(KERN_ERR
+ "shrink_slab: %pF negative objects to delete nr=%ld\n",
shrinker->shrink, total_scan);
total_scan = max_pass;
}
@@ -277,20 +284,33 @@
if (total_scan > max_pass * 2)
total_scan = max_pass * 2;
- trace_mm_shrink_slab_start(shrinker, shrink, nr,
+ trace_mm_shrink_slab_start(shrinker, shrinkctl, nr,
nr_pages_scanned, lru_pages,
max_pass, delta, total_scan);
while (total_scan >= batch_size) {
- int nr_before;
- nr_before = do_shrinker_shrink(shrinker, shrink, 0);
- shrink_ret = do_shrinker_shrink(shrinker, shrink,
- batch_size);
- if (shrink_ret == -1)
- break;
- if (shrink_ret < nr_before)
- ret += nr_before - shrink_ret;
+ if (shrinker->scan_objects) {
+ unsigned long ret;
+ shrinkctl->nr_to_scan = batch_size;
+ ret = shrinker->scan_objects(shrinker, shrinkctl);
+
+ if (ret == SHRINK_STOP)
+ break;
+ freed += ret;
+ } else {
+ int nr_before;
+ long ret;
+
+ nr_before = do_shrinker_shrink(shrinker, shrinkctl, 0);
+ ret = do_shrinker_shrink(shrinker, shrinkctl,
+ batch_size);
+ if (ret == -1)
+ break;
+ if (ret < nr_before)
+ freed += nr_before - ret;
+ }
+
count_vm_events(SLABS_SCANNED, batch_size);
total_scan -= batch_size;
@@ -308,12 +328,12 @@
else
new_nr = atomic_long_read(&shrinker->nr_in_batch);
- trace_mm_shrink_slab_end(shrinker, shrink_ret, nr, new_nr);
+ trace_mm_shrink_slab_end(shrinker, freed, nr, new_nr);
}
up_read(&shrinker_rwsem);
out:
cond_resched();
- return ret;
+ return freed;
}
static inline int is_page_cache_freeable(struct page *page)
