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Date: Fri, 23 Mar 2007 14:41:09 +0000
From: Christoph Hellwig <hch@...radead.org>
To: Tomas M <tomas@...x.org>
Cc: linux-kernel@...r.kernel.org
Subject: Re: [patch] [bugfix] loop.c
On Fri, Mar 23, 2007 at 03:04:54PM +0100, Tomas M wrote:
> I posted this yesterday but it seems people didn't understand the real
> goal of my patch. So I will explain once more again:
>
> This is a bugfix for loop.c block driver, as it currently allocates more
> memory then it needs, without any further use.
>
> If 'max_loop=255' parameter is given, the loop.c driver allocates this
> amount of memory:
>
> kmalloc(max_loop * sizeof(struct loop_device))
>
> But in this case, (max_loop * sizeof) is greater than 65536, and thus
> kmalloc must allocate the next bigger size (which is 128KB of RAM).
>
> Unfortunately the loop.c driver doesn't allow users to use bigger
> max_loop then 255 (for reasons which are completely obsolete) so the
> rest of memory is *unused*.
>
> This patch doesn't fix unused memory in the case of max_loop=255, but
> rather it allows user to specify bigger max_loop (up to 455 on 386), so
> the user can fully use all the memory, which would be allocated anyway.
>
> Thank you for your consideration
The right thing to start with is to split the allocation up, and allocate
each loop device by itself, like in the untested patch below:
After that you're not wasting memory for any off number of loop devices
and can create as many as you have device numbers available:
Index: linux-2.6/drivers/block/loop.c
===================================================================
--- linux-2.6.orig/drivers/block/loop.c 2007-03-23 15:21:57.000000000 +0100
+++ linux-2.6/drivers/block/loop.c 2007-03-23 15:39:44.000000000 +0100
@@ -78,8 +78,7 @@
#include <asm/uaccess.h>
static int max_loop = 8;
-static struct loop_device *loop_dev;
-static struct gendisk **disks;
+static LIST_HEAD(loop_devices);
/*
* Transfer functions
@@ -183,7 +182,7 @@ figure_loop_size(struct loop_device *lo)
if (unlikely((loff_t)x != size))
return -EFBIG;
- set_capacity(disks[lo->lo_number], x);
+ set_capacity(lo->lo_disk, x);
return 0;
}
@@ -812,7 +811,7 @@ static int loop_set_fd(struct loop_devic
lo->lo_queue->queuedata = lo;
lo->lo_queue->unplug_fn = loop_unplug;
- set_capacity(disks[lo->lo_number], size);
+ set_capacity(lo->lo_disk, size);
bd_set_size(bdev, size << 9);
set_blocksize(bdev, lo_blocksize);
@@ -832,7 +831,7 @@ out_clr:
lo->lo_device = NULL;
lo->lo_backing_file = NULL;
lo->lo_flags = 0;
- set_capacity(disks[lo->lo_number], 0);
+ set_capacity(lo->lo_disk, 0);
invalidate_bdev(bdev, 0);
bd_set_size(bdev, 0);
mapping_set_gfp_mask(mapping, lo->old_gfp_mask);
@@ -918,7 +917,7 @@ static int loop_clr_fd(struct loop_devic
memset(lo->lo_crypt_name, 0, LO_NAME_SIZE);
memset(lo->lo_file_name, 0, LO_NAME_SIZE);
invalidate_bdev(bdev, 0);
- set_capacity(disks[lo->lo_number], 0);
+ set_capacity(lo->lo_disk, 0);
bd_set_size(bdev, 0);
mapping_set_gfp_mask(filp->f_mapping, gfp);
lo->lo_state = Lo_unbound;
@@ -1383,7 +1382,7 @@ int loop_unregister_transfer(int number)
xfer_funcs[n] = NULL;
- for (lo = &loop_dev[0]; lo < &loop_dev[max_loop]; lo++) {
+ list_for_each_entry(lo, &loop_devices, lo_list) {
mutex_lock(&lo->lo_ctl_mutex);
if (lo->lo_encryption == xfer)
@@ -1398,9 +1397,56 @@ int loop_unregister_transfer(int number)
EXPORT_SYMBOL(loop_register_transfer);
EXPORT_SYMBOL(loop_unregister_transfer);
+static int __init loop_init_one(int i)
+{
+ struct loop_device *lo;
+
+ lo = kzalloc(sizeof(*lo), GFP_KERNEL);
+ if (!lo)
+ goto out;
+
+ lo->lo_queue = blk_alloc_queue(GFP_KERNEL);
+ if (!lo->lo_queue)
+ goto out_free_dev;
+ lo->lo_disk = alloc_disk(1);
+ if (!lo->lo_disk)
+ goto out_free_queue;
+ mutex_init(&lo->lo_ctl_mutex);
+ lo->lo_number = i;
+ lo->lo_thread = NULL;
+ init_waitqueue_head(&lo->lo_event);
+ spin_lock_init(&lo->lo_lock);
+ list_add(&lo->lo_list, &loop_devices);
+ lo->lo_disk->major = LOOP_MAJOR;
+ lo->lo_disk->first_minor = i;
+ lo->lo_disk->fops = &lo_fops;
+ sprintf(lo->lo_disk->disk_name, "loop%d", i);
+ lo->lo_disk->private_data = lo;
+ lo->lo_disk->queue = lo->lo_queue;
+ add_disk(lo->lo_disk);
+ return 0;
+
+ out_free_queue:
+ blk_cleanup_queue(lo->lo_queue);
+ out_free_dev:
+ kfree(lo);
+ out:
+ return -ENOMEM;
+}
+
+static void loop_del_one(struct loop_device *lo)
+{
+ del_gendisk(lo->lo_disk);
+ blk_cleanup_queue(lo->lo_queue);
+ put_disk(lo->lo_disk);
+ list_del(&lo->lo_list);
+ kfree(lo);
+}
+
static int __init loop_init(void)
{
- int i;
+ struct loop_device *lo, *next;
+ int err, i;
if (max_loop < 1 || max_loop > 256) {
printk(KERN_WARNING "loop: invalid max_loop (must be between"
@@ -1411,78 +1457,32 @@ static int __init loop_init(void)
if (register_blkdev(LOOP_MAJOR, "loop"))
return -EIO;
- loop_dev = kmalloc(max_loop * sizeof(struct loop_device), GFP_KERNEL);
- if (!loop_dev)
- goto out_mem1;
- memset(loop_dev, 0, max_loop * sizeof(struct loop_device));
-
- disks = kmalloc(max_loop * sizeof(struct gendisk *), GFP_KERNEL);
- if (!disks)
- goto out_mem2;
-
for (i = 0; i < max_loop; i++) {
- disks[i] = alloc_disk(1);
- if (!disks[i])
- goto out_mem3;
+ err = loop_init_one(i);
+ if (err)
+ goto out_free_devs;
}
- for (i = 0; i < max_loop; i++) {
- struct loop_device *lo = &loop_dev[i];
- struct gendisk *disk = disks[i];
-
- memset(lo, 0, sizeof(*lo));
- lo->lo_queue = blk_alloc_queue(GFP_KERNEL);
- if (!lo->lo_queue)
- goto out_mem4;
- mutex_init(&lo->lo_ctl_mutex);
- lo->lo_number = i;
- lo->lo_thread = NULL;
- init_waitqueue_head(&lo->lo_event);
- spin_lock_init(&lo->lo_lock);
- disk->major = LOOP_MAJOR;
- disk->first_minor = i;
- disk->fops = &lo_fops;
- sprintf(disk->disk_name, "loop%d", i);
- disk->private_data = lo;
- disk->queue = lo->lo_queue;
- }
-
- /* We cannot fail after we call this, so another loop!*/
- for (i = 0; i < max_loop; i++)
- add_disk(disks[i]);
printk(KERN_INFO "loop: loaded (max %d devices)\n", max_loop);
return 0;
-out_mem4:
- while (i--)
- blk_cleanup_queue(loop_dev[i].lo_queue);
- i = max_loop;
-out_mem3:
- while (i--)
- put_disk(disks[i]);
- kfree(disks);
-out_mem2:
- kfree(loop_dev);
-out_mem1:
+ out_free_devs:
+ list_for_each_entry_safe(lo, next, &loop_devices, lo_list)
+ loop_del_one(lo);
unregister_blkdev(LOOP_MAJOR, "loop");
printk(KERN_ERR "loop: ran out of memory\n");
- return -ENOMEM;
+ return err;
}
static void loop_exit(void)
{
- int i;
+ struct loop_device *lo, *next;
+
+ list_for_each_entry_safe(lo, next, &loop_devices, lo_list)
+ loop_del_one(lo);
- for (i = 0; i < max_loop; i++) {
- del_gendisk(disks[i]);
- blk_cleanup_queue(loop_dev[i].lo_queue);
- put_disk(disks[i]);
- }
if (unregister_blkdev(LOOP_MAJOR, "loop"))
printk(KERN_WARNING "loop: cannot unregister blkdev\n");
-
- kfree(disks);
- kfree(loop_dev);
}
module_init(loop_init);
Index: linux-2.6/include/linux/loop.h
===================================================================
--- linux-2.6.orig/include/linux/loop.h 2007-03-23 15:23:32.000000000 +0100
+++ linux-2.6/include/linux/loop.h 2007-03-23 15:30:40.000000000 +0100
@@ -64,6 +64,8 @@ struct loop_device {
wait_queue_head_t lo_event;
request_queue_t *lo_queue;
+ struct gendisk *lo_disk;
+ struct list_head lo_list;
};
#endif /* __KERNEL__ */
-
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