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Message-ID: <20090916162457.GA84213@freezingfog.local>
Date: Wed, 16 Sep 2009 11:24:57 -0500
From: Will Drewry <redpig@...aspill.org>
To: linux-ext4@...r.kernel.org
Subject: [PATCH][RFC] resize2fs and uninit_bg questions
Hi linux-ext4,
I have a two questions with an accompanying patch for clarification.
resize2fs is uninit_bg aware, but when it is expanding an ext4
filesystem, it will always zero the inode tables. Is it safe to mimick
mke2fs's write_inode_table(.., lazy_flag=1) and leave the new block
groups' inode tables marked INODE_UNINIT, BLOCK_UNINIT and _not_ zero
out the inode table if uninit_bg is supported?
If it is okay, then it means offline resizing upwards can be just as
fast as mke2fs. I've attached a patch which is probably incomplete.
I'd love feedback as to the feasibility of the change and/or patch
quality.
As a follow-on, would it be sane to add support like this for
online resizing. From a cursory investigation, it looks like
setup_new_block_groups() could be modified to not zero itables
if uninit_bg is supported, and INODE_ZEROED could be replaced
with ΒG_*_UNINIT. However, I'm not sure if that is a naive
view. I'm happy to send along a patch illustrating this change
if that'd be helpful or welcome.
Any and all feedback is appreciated -- even if it just for me
to look at the archives/link/etc.
Thanks!
Signed-off-by: Will Drewry <redpig@...aspill.org>
---
resize/resize2fs.c | 28 ++++++++++++++++++++++------
1 files changed, 22 insertions(+), 6 deletions(-)
diff --git a/resize/resize2fs.c b/resize/resize2fs.c
index 1a5d910..9fcc3b9 100644
--- a/resize/resize2fs.c
+++ b/resize/resize2fs.c
@@ -497,8 +497,7 @@ retry:
fs->group_desc[i].bg_flags = 0;
if (csum_flag)
- fs->group_desc[i].bg_flags |= EXT2_BG_INODE_UNINIT |
- EXT2_BG_INODE_ZEROED;
+ fs->group_desc[i].bg_flags |= EXT2_BG_INODE_UNINIT;
if (i == fs->group_desc_count-1) {
numblocks = (fs->super->s_blocks_count -
fs->super->s_first_data_block) %
@@ -568,7 +567,7 @@ errout:
static errcode_t adjust_superblock(ext2_resize_t rfs, blk_t new_size)
{
ext2_filsys fs;
- int adj = 0;
+ int adj = 0, csum_flag = 0, num = 0;
errcode_t retval;
blk_t group_block;
unsigned long i;
@@ -624,6 +623,9 @@ static errcode_t adjust_superblock(ext2_resize_t rfs, blk_t new_size)
&rfs->itable_buf);
if (retval)
goto errout;
+ /* Track if we can get by with a lazy init */
+ csum_flag = EXT2_HAS_RO_COMPAT_FEATURE(fs->super,
+ EXT4_FEATURE_RO_COMPAT_GDT_CSUM);
memset(rfs->itable_buf, 0, fs->blocksize * fs->inode_blocks_per_group);
group_block = fs->super->s_first_data_block +
@@ -642,10 +644,24 @@ static errcode_t adjust_superblock(ext2_resize_t rfs, blk_t new_size)
/*
* Write out the new inode table
*/
+ if (csum_flag) {
+ /* These are _new_ inode tables. No inodes should be in use.
+ * (As per ext2fs_set_gdt_csum) */
+ fs->group_desc[i].bg_itable_unused = fs->super->s_inodes_per_group;
+ num = ((((fs->super->s_inodes_per_group -
+ fs->group_desc[i].bg_itable_unused) *
+ EXT2_INODE_SIZE(fs->super)) +
+ EXT2_BLOCK_SIZE(fs->super) - 1) /
+ EXT2_BLOCK_SIZE(fs->super));
+ } else {
+ num = fs->inode_blocks_per_group;
+ /* The kernel doesn't need to zero the itable blocks. We will below */
+ fs->group_desc[i].bg_flags |= EXT2_BG_INODE_ZEROED;
+ }
retval = io_channel_write_blk(fs->io,
- fs->group_desc[i].bg_inode_table,
- fs->inode_blocks_per_group,
- rfs->itable_buf);
+ fs->group_desc[i].bg_inode_table, /* blk */
+ num, /* count */
+ rfs->itable_buf); /* contents */
if (retval) goto errout;
io_channel_flush(fs->io);
--
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