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SubjectRe: [Ext2-devel] [PATCH] distributed counters for ext2 to avoid group scaning
On Mon, Mar 17, 2003 at 06:09:54PM +0300, Alex Tomas wrote:
> >>>>> Matthew Wilcox (MW) writes:
> MW> And then we have 3 of these (an additional 3k..). Per
> MW> blockgroup. My 4GB / has 30 blockgroups; my 30GB /home has 232.
> MW> So that's a little under 8 per GB. My _laptop_ has a 40GB drive,
> MW> so that's on the order of 320 blockgroups -- almost an additional
> MW> megabyte of ram consumed for these counters.
> no-no!
> _one_ dcounter to maintain number of free blocks _per_ fs.
> _one_ dcounter to maintain number of inode blocks _per_ fs.
> _one_ dcounter to maintain number of dirs _per_ fs.
> 3 dcounter per fs. no more.

Gah. That's your fault. Use diff -p in future; I saw:

diff -uNr linux/include/linux/ext2_fs_sb.h edited/include/linux/ext2_fs_sb.h
--- linux/include/linux/ext2_fs_sb.h Sun Mar 16 17:21:34 2003
+++ edited/include/linux/ext2_fs_sb.h Mon Mar 17 00:12:00 2003
@@ -16,6 +16,8 @@
#ifndef _LINUX_EXT2_FS_SB
#define _LINUX_EXT2_FS_SB

+#include <linux/dcounter.h>
struct ext2_bg_info {
u8 debts;
spinlock_t balloc_lock;
@@ -52,6 +54,9 @@
u32 s_next_generation;
unsigned long s_dir_count;
struct ext2_bg_info *s_bgi;
+ struct dcounter free_blocks_dc;
+ struct dcounter free_inodes_dc;
+ struct dcounter dirs_dc;

which makes it look like the dcounters are added to ext2_bg_info.
diff -p would have put the name of the struct after the @@ line. Not to
mention you didn't follow the `s_' prefix style used everywhere else in
that struct.

Anyway, I think dcounters should probably be allocated from kmalloc_percpu()
rather than as part of the dcounter struct.
"It's not Hollywood. War is real, war is primarily not about defeat or
victory, it is about death. I've seen thousands and thousands of dead bodies.
Do you think I want to have an academic debate on this subject?" -- Robert Fisk
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