Allow setting a custom memory cost limit for the in-memory NSCache. This can help to keep memory down before memory warnings are sent by the device.

SDWebImage/SDImageCache.h

@@ -32,6 +32,11 @@ typedef enum SDImageCacheType SDImageCacheType;
  */
 @interface SDImageCache : NSObject
 
+/**
+ * The maximum "total cost" of the in-memory image cache. The cost function is the number of pixels held in memory.
+ */
+@property (assign, nonatomic) NSInteger maxMemoryCost;
+
 /**
  * The maximum length of time to keep an image in the cache, in seconds
  */

SDWebImage/SDImageCache.m

@@ -338,6 +338,11 @@ static const NSInteger kDefaultCacheMaxCacheAge = 60 * 60 * 24 * 7; // 1 week
     }
 }
 
+- (void)setMaxMemoryCost:(NSInteger)maxMemoryCost
+{
+    self.memCache.totalCostLimit = maxMemoryCost;
+}
+
 - (void)clearMemory
 {
     [self.memCache removeAllObjects];