From f4be591f1436afff4a18ddd180f7bf9421ffddfe Mon Sep 17 00:00:00 2001 From: Calvin Owens Date: Fri, 16 Apr 2021 14:18:29 -0700 Subject: brd: expose number of allocated pages in debugfs While the maximum size of each ramdisk is defined either as a module parameter, or compile time default, it's impossible to know how many pages have currently been allocated by each ram%d device, since they're allocated when used and never freed. This patch creates a new directory at this location: /sys/kernel/debug/ramdisk_pages/ which will contain a file named "ram%d" for each instantiated ramdisk on the system. The file is read-only, and read() will output the number of pages currently held by that ramdisk. We lose track how much memory a ramdisk is using as pages once used are simply recycled but never freed. In instances where we exhaust the size of the ramdisk with a file that exceeds it, encounter ENOSPC and delete the file for mitigation; df would show decrease in used and increase in available blocks but the since we have touched all pages, the memory footprint of the ramdisk does not reflect the blocks used/available count ... [root@localhost ~]# mkfs.ext2 /dev/ram15 mke2fs 1.45.6 (20-Mar-2020) Creating filesystem with 4096 1k blocks and 1024 inodes [root@localhost ~]# mount /dev/ram15 /mnt/ram15/ [root@localhost ~]# cat /sys/kernel/debug/ramdisk_pages/ram15 58 [root@kerneltest008.06.prn3 ~]# df /dev/ram15 Filesystem 1K-blocks Used Available Use% Mounted on /dev/ram15 3963 31 3728 1% /mnt/ram15 [root@kerneltest008.06.prn3 ~]# dd if=/dev/urandom of=/mnt/ram15/test2 bs=1M count=5 dd: error writing '/mnt/ram15/test2': No space left on device 4+0 records in 3+0 records out 4005888 bytes (4.0 MB, 3.8 MiB) copied, 0.0446614 s, 89.7 MB/s [root@kerneltest008.06.prn3 ~]# df /mnt/ram15/ Filesystem 1K-blocks Used Available Use% Mounted on /dev/ram15 3963 3960 0 100% /mnt/ram15 [root@kerneltest008.06.prn3 ~]# cat /sys/kernel/debug/ramdisk_pages/ram15 1024 [root@kerneltest008.06.prn3 ~]# rm /mnt/ram15/test2 rm: remove regular file '/mnt/ram15/test2'? y [root@kerneltest008.06.prn3 /var]# df /dev/ram15 Filesystem 1K-blocks Used Available Use% Mounted on /dev/ram15 3963 31 3728 1% /mnt/ram15 # Acutal memory footprint [root@kerneltest008.06.prn3 /var]# cat /sys/kernel/debug/ramdisk_pages/ram15 1024 ... This debugfs counter will always reveal the accurate number of permanently allocated pages to the ramdisk. Signed-off-by: Calvin Owens [cleaned up the !CONFIG_DEBUG_FS case and API changes for HEAD] Signed-off-by: Kyle McMartin [rebased] Signed-off-by: Saravanan D Signed-off-by: Jens Axboe --- drivers/block/brd.c | 19 ++++++++++++++++++- 1 file changed, 18 insertions(+), 1 deletion(-) (limited to 'drivers/block') diff --git a/drivers/block/brd.c b/drivers/block/brd.c index 18bf99906662..6e622c1327ee 100644 --- a/drivers/block/brd.c +++ b/drivers/block/brd.c @@ -22,6 +22,7 @@ #include #include #include +#include #include @@ -48,6 +49,7 @@ struct brd_device { */ spinlock_t brd_lock; struct radix_tree_root brd_pages; + u64 brd_nr_pages; }; /* @@ -116,6 +118,8 @@ static struct page *brd_insert_page(struct brd_device *brd, sector_t sector) page = radix_tree_lookup(&brd->brd_pages, idx); BUG_ON(!page); BUG_ON(page->index != idx); + } else { + brd->brd_nr_pages++; } spin_unlock(&brd->brd_lock); @@ -365,11 +369,13 @@ __setup("ramdisk_size=", ramdisk_size); */ static LIST_HEAD(brd_devices); static DEFINE_MUTEX(brd_devices_mutex); +static struct dentry *brd_debugfs_dir; static struct brd_device *brd_alloc(int i) { struct brd_device *brd; struct gendisk *disk; + char buf[DISK_NAME_LEN]; brd = kzalloc(sizeof(*brd), GFP_KERNEL); if (!brd) @@ -382,6 +388,11 @@ static struct brd_device *brd_alloc(int i) if (!brd->brd_queue) goto out_free_dev; + snprintf(buf, DISK_NAME_LEN, "ram%d", i); + if (!IS_ERR_OR_NULL(brd_debugfs_dir)) + debugfs_create_u64(buf, 0444, brd_debugfs_dir, + &brd->brd_nr_pages); + /* This is so fdisk will align partitions on 4k, because of * direct_access API needing 4k alignment, returning a PFN * (This is only a problem on very small devices <= 4M, @@ -397,7 +408,7 @@ static struct brd_device *brd_alloc(int i) disk->fops = &brd_fops; disk->private_data = brd; disk->flags = GENHD_FL_EXT_DEVT; - sprintf(disk->disk_name, "ram%d", i); + strlcpy(disk->disk_name, buf, DISK_NAME_LEN); set_capacity(disk, rd_size * 2); /* Tell the block layer that this is not a rotational device */ @@ -495,6 +506,8 @@ static int __init brd_init(void) brd_check_and_reset_par(); + brd_debugfs_dir = debugfs_create_dir("ramdisk_pages", NULL); + mutex_lock(&brd_devices_mutex); for (i = 0; i < rd_nr; i++) { brd = brd_alloc(i); @@ -519,6 +532,8 @@ static int __init brd_init(void) return 0; out_free: + debugfs_remove_recursive(brd_debugfs_dir); + list_for_each_entry_safe(brd, next, &brd_devices, brd_list) { list_del(&brd->brd_list); brd_free(brd); @@ -534,6 +549,8 @@ static void __exit brd_exit(void) { struct brd_device *brd, *next; + debugfs_remove_recursive(brd_debugfs_dir); + list_for_each_entry_safe(brd, next, &brd_devices, brd_list) brd_del_one(brd); -- cgit v1.2.3