Commit 9db5579b authored by Nick Piggin's avatar Nick Piggin Committed by Linus Torvalds

rewrite rd

This is a rewrite of the ramdisk block device driver.

The old one is really difficult because it effectively implements a block
device which serves data out of its own buffer cache.  It relies on the dirty
bit being set, to pin its backing store in cache, however there are non
trivial paths which can clear the dirty bit (eg.  try_to_free_buffers()),
which had recently lead to data corruption.  And in general it is completely
wrong for a block device driver to do this.

The new one is more like a regular block device driver.  It has no idea about
vm/vfs stuff.  It's backing store is similar to the buffer cache (a simple
radix-tree of pages), but it doesn't know anything about page cache (the pages
in the radix tree are not pagecache pages).

There is one slight downside -- direct block device access and filesystem
metadata access goes through an extra copy and gets stored in RAM twice.
However, this downside is only slight, because the real buffercache of the
device is now reclaimable (because we're not playing crazy games with it), so
under memory intensive situations, footprint should effectively be the same --
maybe even a slight advantage to the new driver because it can also reclaim
buffer heads.

The fact that it now goes through all the regular vm/fs paths makes it
much more useful for testing, too.

   text    data     bss     dec     hex filename
   2837     849     384    4070     fe6 drivers/block/rd.o
   3528     371      12    3911     f47 drivers/block/brd.o

Text is larger, but data and bss are smaller, making total size smaller.

A few other nice things about it:
- Similar structure and layout to the new loop device handlinag.
- Dynamic ramdisk creation.
- Runtime flexible buffer head size (because it is no longer part of the
  ramdisk code).
- Boot / load time flexible ramdisk size, which could easily be extended
  to a per-ramdisk runtime changeable size (eg. with an ioctl).
- Can use highmem for the backing store.

[ fix build]
[ make rd_size non-static]
Signed-off-by: default avatarNick Piggin <>
Signed-off-by: default avatarByron Bradley <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent daeb51e6
......@@ -3254,6 +3254,11 @@ W:
S: Maintained
F: drivers/net/wireless/rt2x00/
P: Nick Piggin
S: Maintained
P: Matt Mackall
......@@ -322,7 +322,7 @@ config BLK_DEV_UB
If unsure, say N.
config BLK_DEV_RAM
tristate "RAM disk support"
tristate "RAM block device support"
Saying Y here will allow you to use a portion of your RAM memory as
a block device, so that you can make file systems on it, read and
......@@ -357,16 +357,6 @@ config BLK_DEV_RAM_SIZE
The default value is 4096 kilobytes. Only change this if you know
what you are doing.
int "Default RAM disk block size (bytes)"
depends on BLK_DEV_RAM
default "1024"
The default value is 1024 bytes. PAGE_SIZE is a much more
efficient choice however. The default is kept to ensure initrd
setups function - apparently needed by the rd_load_image routine
that supposes the filesystem in the image uses a 1024 blocksize.
tristate "Packet writing on CD/DVD media"
depends on !UML
......@@ -11,7 +11,7 @@ obj-$(CONFIG_AMIGA_FLOPPY) += amiflop.o
obj-$(CONFIG_PS3_DISK) += ps3disk.o
obj-$(CONFIG_ATARI_FLOPPY) += ataflop.o
obj-$(CONFIG_AMIGA_Z2RAM) += z2ram.o
obj-$(CONFIG_BLK_DEV_RAM) += rd.o
obj-$(CONFIG_BLK_DEV_RAM) += brd.o
obj-$(CONFIG_BLK_DEV_LOOP) += loop.o
obj-$(CONFIG_BLK_DEV_PS2) += ps2esdi.o
obj-$(CONFIG_BLK_DEV_XD) += xd.o
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......@@ -1436,6 +1436,7 @@ void invalidate_bh_lrus(void)
on_each_cpu(invalidate_bh_lru, NULL, 1, 1);
void set_bh_page(struct buffer_head *bh,
struct page *page, unsigned long offset)
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