UBIFS: do not print scary memory allocation warnings

Bulk-read allocates a lot of memory with 'kmalloc()', and when it
is/gets fragmented 'kmalloc()' fails with a scarry warning. But
because bulk-read is just an optimization, UBIFS keeps working fine.
Supress the warning by passing __GFP_NOWARN option to 'kmalloc()'.

This patch also introduces a macro for the magic 128KiB constant.
This is just neater.

Note, this is not really fixes the problem we had, but just hides
the warnings. The further patches fix the problem.

Signed-off-by: Artem Bityutskiy <[e-mail]>

fs/ubifs/file.c

···
 	int err, page_idx, page_cnt, ret = 0, n = 0;
 	loff_t isize;
 
-	bu = kmalloc(sizeof(struct bu_info), GFP_NOFS);
+	bu = kmalloc(sizeof(struct bu_info), GFP_NOFS | __GFP_NOWARN);
 	if (!bu)
 		return 0;
 
 	bu->buf_len = c->bulk_read_buf_size;
-	bu->buf = kmalloc(bu->buf_len, GFP_NOFS);
+	bu->buf = kmalloc(bu->buf_len, GFP_NOFS | __GFP_NOWARN);
 	if (!bu->buf)
 		goto out_free;
 

fs/ubifs/super.c

···
 #include <linux/mount.h>
 #include "ubifs.h"
 
+/*
+ * Maximum amount of memory we may 'kmalloc()' without worrying that we are
+ * allocating too much.
+ */
+#define UBIFS_KMALLOC_OK (128*1024)
+
 /* Slab cache for UBIFS inodes */
 struct kmem_cache *ubifs_inode_slab;
 
···
 	 * calculations when reporting free space.
 	 */
 	c->leb_overhead = c->leb_size % UBIFS_MAX_DATA_NODE_SZ;
+
 	/* Buffer size for bulk-reads */
 	c->bulk_read_buf_size = UBIFS_MAX_BULK_READ * UBIFS_MAX_DATA_NODE_SZ;
 	if (c->bulk_read_buf_size > c->leb_size)
 		c->bulk_read_buf_size = c->leb_size;
-	if (c->bulk_read_buf_size > 128 * 1024) {
-		/* Check if we can kmalloc more than 128KiB */
-		void *try = kmalloc(c->bulk_read_buf_size, GFP_KERNEL);
-
+	if (c->bulk_read_buf_size > UBIFS_KMALLOC_OK) {
+		/* Check if we can kmalloc that much */
+		void *try = kmalloc(c->bulk_read_buf_size,
+				    GFP_KERNEL | __GFP_NOWARN);
 		kfree(try);
 		if (!try)
-			c->bulk_read_buf_size = 128 * 1024;
+			c->bulk_read_buf_size = UBIFS_KMALLOC_OK;
 	}
 	return 0;
 }

fs/ubifs/ubifs.h

···
 };
 
 /**
- * struct bu_info - bulk-read information
+ * struct bu_info - bulk-read information.
  * @key: first data node key
  * @zbranch: zbranches of data nodes to bulk read
  * @buf: buffer to read into