Re: [Ext2-devel] [PATCH] distributed counters for ext2 to avoid group scaning

From: Matthew Wilcox (willy@debian.org)
Date: Mon Mar 17 2003 - 10:27:19 EST

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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This archive was generated by hypermail 2b29 : Sun Mar 23 2003 - 22:00:20 EST