block/partitions: optimize memory allocation in check_partition()

Currently, sizeof(struct parsed_partitions) may be 64KB in 32bit arch, so
it is easy to trigger page allocation failure by check_partition,
especially in hotplug block device situation(such as, USB mass storage,
MMC card, ...), and Felipe Balbi has observed the failure.

This patch does below optimizations on the allocation of struct
parsed_partitions to try to address the issue:

- make parsed_partitions.parts as pointer so that the pointed memory can
  fit in 32KB buffer, then approximate 32KB memory can be saved

- vmalloc the buffer pointed by parsed_partitions.parts because 32KB is
  still a bit big for kmalloc

- given that many devices have the partition count limit, so only
  allocate disk_max_parts() partitions instead of 256 partitions always

Signed-off-by: Ming Lei <ming.lei@canonical.com>
Reported-by: Felipe Balbi <balbi@ti.com>
Cc: Jens Axboe <axboe@kernel.dk>
Reviewed-by: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

block/partition-generic.c

@@ -418,7 +418,7 @@ int rescan_partitions(struct gendisk *disk, struct block_device *bdev)
 	int p, highest, res;
 rescan:
 	if (state && !IS_ERR(state)) {
-		kfree(state);
+		free_partitions(state);
 		state = NULL;
 	}
 
@@ -525,7 +525,7 @@ int rescan_partitions(struct gendisk *disk, struct block_device *bdev)
 			md_autodetect_dev(part_to_dev(part)->devt);
 #endif
 	}
-	kfree(state);
+	free_partitions(state);
 	return 0;
 }
 

block/partitions/check.c

@@ -14,6 +14,7 @@
  */
 
 #include <linux/slab.h>
+#include <linux/vmalloc.h>
 #include <linux/ctype.h>
 #include <linux/genhd.h>
 
@@ -106,18 +107,45 @@ static int (*check_part[])(struct parsed_partitions *) = {
 	NULL
 };
 
+static struct parsed_partitions *allocate_partitions(struct gendisk *hd)
+{
+	struct parsed_partitions *state;
+	int nr;
+
+	state = kzalloc(sizeof(*state), GFP_KERNEL);
+	if (!state)
+		return NULL;
+
+	nr = disk_max_parts(hd);
+	state->parts = vzalloc(nr * sizeof(state->parts[0]));
+	if (!state->parts) {
+		kfree(state);
+		return NULL;
+	}
+
+	state->limit = nr;
+
+	return state;
+}
+
+void free_partitions(struct parsed_partitions *state)
+{
+	vfree(state->parts);
+	kfree(state);
+}
+
 struct parsed_partitions *
 check_partition(struct gendisk *hd, struct block_device *bdev)
 {
 	struct parsed_partitions *state;
 	int i, res, err;
 
-	state = kzalloc(sizeof(struct parsed_partitions), GFP_KERNEL);
+	state = allocate_partitions(hd);
 	if (!state)
 		return NULL;
 	state->pp_buf = (char *)__get_free_page(GFP_KERNEL);
 	if (!state->pp_buf) {
-		kfree(state);
+		free_partitions(state);
 		return NULL;
 	}
 	state->pp_buf[0] = '\0';
@@ -128,10 +156,9 @@ check_partition(struct gendisk *hd, struct block_device *bdev)
 	if (isdigit(state->name[strlen(state->name)-1]))
 		sprintf(state->name, "p");
 
-	state->limit = disk_max_parts(hd);
 	i = res = err = 0;
 	while (!res && check_part[i]) {
-		memset(&state->parts, 0, sizeof(state->parts));
+		memset(state->parts, 0, state->limit * sizeof(state->parts[0]));
 		res = check_part[i++](state);
 		if (res < 0) {
 			/* We have hit an I/O error which we don't report now.
@@ -161,6 +188,6 @@ check_partition(struct gendisk *hd, struct block_device *bdev)
 	printk(KERN_INFO "%s", state->pp_buf);
 
 	free_page((unsigned long)state->pp_buf);
-	kfree(state);
+	free_partitions(state);
 	return ERR_PTR(res);
 }

block/partitions/check.h

@@ -15,13 +15,15 @@ struct parsed_partitions {
 		int flags;
 		bool has_info;
 		struct partition_meta_info info;
-	} parts[DISK_MAX_PARTS];
+	} *parts;
 	int next;
 	int limit;
 	bool access_beyond_eod;
 	char *pp_buf;
 };
 
+void free_partitions(struct parsed_partitions *state);
+
 struct parsed_partitions *
 check_partition(struct gendisk *, struct block_device *);