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Date: Fri, 7 Dec 2007 03:14:28 -0700
From: Andreas Dilger <adilger@....com>
To: "Jose R. Santos" <jrs@...ibm.com>
Cc: linux-ext4 <linux-ext4@...r.kernel.org>
Subject: Re: [RFC] [PATCH] Flex_BG ialloc awareness V2.
On Dec 06, 2007 16:10 -0600, Jose R. Santos wrote:
> @@ -600,6 +600,7 @@ void ext4_free_blocks_sb(handle_t *handle, struct super_block *sb,
> struct ext4_sb_info *sbi;
> int err = 0, ret;
> ext4_grpblk_t group_freed;
> + ext4_group_t flex_group;
>
> *pdquot_freed_blocks = 0;
> sbi = EXT4_SB(sb);
> @@ -745,6 +746,14 @@ do_more:
> spin_unlock(sb_bgl_lock(sbi, block_group));
> percpu_counter_add(&sbi->s_freeblocks_counter, count);
>
> + if (EXT4_HAS_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_FLEX_BG) &&
> + sbi->s_groups_per_flex_shift) {
> + flex_group = ext4_flex_group(sbi, block_group);
> + spin_lock(sb_bgl_lock(sbi, flex_group));
> + sbi->s_flex_groups[flex_group].free_blocks += count;
> + spin_unlock(sb_bgl_lock(sbi, flex_group));
> + }
In general, I prefer to keep variables in as local a scope as possible.
In this case, flex_group could be declared inside the "if (EXT4_HAS_INCOMPAT"
check.
> @@ -1610,6 +1619,7 @@ ext4_fsblk_t ext4_new_blocks_old(handle_t *handle, struct inode *inode,
> unsigned short windowsz = 0;
> ext4_group_t ngroups;
> unsigned long num = *count;
> + ext4_group_t flex_group;
>
> *errp = -ENOSPC;
> sb = inode->i_sb;
> @@ -1815,6 +1825,14 @@ allocated:
> spin_unlock(sb_bgl_lock(sbi, group_no));
> percpu_counter_sub(&sbi->s_freeblocks_counter, num);
>
> + if (EXT4_HAS_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_FLEX_BG) &&
> + sbi->s_groups_per_flex_shift) {
> + flex_group = ext4_flex_group(sbi, group_no);
> + spin_lock(sb_bgl_lock(sbi, flex_group));
> + sbi->s_flex_groups[flex_group].free_blocks -= num;
> + spin_unlock(sb_bgl_lock(sbi, flex_group));
> + }
Same as above.
> @@ -158,6 +158,7 @@ void ext4_free_inode (handle_t *handle, struct inode * inode)
> struct ext4_super_block * es;
> struct ext4_sb_info *sbi;
> int fatal = 0, err;
> + ext4_group_t flex_group;
>
> if (atomic_read(&inode->i_count) > 1) {
> printk ("ext4_free_inode: inode has count=%d\n",
> @@ -235,6 +236,13 @@ void ext4_free_inode (handle_t *handle, struct inode * inode)
> if (is_directory)
> percpu_counter_dec(&sbi->s_dirs_counter);
>
> + if (EXT4_HAS_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_FLEX_BG) &&
> + sbi->s_groups_per_flex_shift) {
> + flex_group = ext4_flex_group(sbi, block_group);
> + spin_lock(sb_bgl_lock(sbi, flex_group));
> + sbi->s_flex_groups[flex_group].free_inodes++;
> + spin_unlock(sb_bgl_lock(sbi, flex_group));
> + }
Same as above...
> +#define free_block_ratio 10
> +
> +int find_group_flex(struct super_block *sb, struct inode *parent)
> +{
> + n_fbg_groups = (sbi->s_groups_count + flex_size - 1) / flex_size;
> + best_flex = parent_fbg_group;
> +
> +find_close_to_parent:
> + flex_freeb_ratio = flex_group[best_flex].free_blocks*100/blocks_per_flex;
There is no particular reason that this ratio needs to be "*100", it could
just as easily be a fraction of 256 and make the multiply into a shift.
The free_block_ratio would be 26 in that case.
> + for (i = 0; i < n_fbg_groups; i++) {
> + if (i == parent_fbg_group || i == parent_fbg_group - 1)
> + continue;
It seems this scans flex groups the way we used to scan groups?
> +found_flexbg:
> + for (i = best_flex * flex_size; i < ngroups &&
> + i < (best_flex + 1) * flex_size; i++) {
And now that we've found a suitable flex group, we need to find which
block group therein has some free inodes...
> +static int ext4_fill_flex_info(struct super_block *sb)
> +{
It still seems desirable to have a single per-group array instead of
> @@ -622,7 +631,9 @@ struct ext4_super_block {
> __le16 s_mmp_interval; /* # seconds to wait in MMP checking */
> __le64 s_mmp_block; /* Block for multi-mount protection */
> __le32 s_raid_stripe_width; /* blocks on all data disks (N*stride)*/
> - __u32 s_reserved[163]; /* Padding to the end of the block */
> + __le16 s_flex_bg_size; /* FLEX_BG group size */
Shouldn't this be "s_flex_bg_bits"?
> +{
> + return block_group >> sbi->s_groups_per_flex_shift;
> +}
> +
> +static inline unsigned int ext4_flex_bg_size(struct ext4_sb_info *sbi)
> +{
> + return 1 << sbi->s_groups_per_flex_shift;
> +}
> +
> #define ext4_std_error(sb, errno) \
> do { \
> if ((errno)) \
> diff --git a/lib/ext2fs/alloc_tables.c b/lib/ext2fs/alloc_tables.c
> --- a/lib/ext2fs/alloc_tables.c
> +++ b/lib/ext2fs/alloc_tables.c
> + if (EXT2_HAS_INCOMPAT_FEATURE (fs->super,
> + EXT4_FEATURE_INCOMPAT_FLEX_BG))
> + ext2fs_allocate_flex_groups(fs);
> +
> + else {
> + for (i = 0; i < fs->group_desc_count; i++) {
> + retval = ext2fs_allocate_group_table(fs, i, fs->block_map);
> + if (retval)
> + return retval;
> + }
> }
My preference would be to have "if (EXT2_HAS_INCOMPAT...) { ... } else {"
(i.e. add { } for the first part) since there are { } on the second part,
and it is just easier to read.
> @@ -1045,6 +1046,19 @@ static void PRS(int argc, char *argv[])
> + if ((flex_bg_size & (flex_bg_size-1)) != 0) {
> + com_err(program_name, 0,
> + _("Flex_BG size must be a power of 2"));
> + exit(1);
If flex_bg_size is a power of two then there isn't any need to store anything
except __u8 s_flex_bg_bits in the superblock.
> @@ -1444,6 +1458,10 @@ static void PRS(int argc, char *argv[])
> + if(flex_bg_size) {
> + fs_param.s_flex_bg_size = ext2fs_swab16(flex_bg_size);
> + }
Space between if and (, and no need for braces for a single line body.
It would also be nice to get a m_flexbg test case along with this patch
that (at minimum) creates a filesystem with flexbg enabled, and then
runs e2fsck on it. This was broken for the lazy_bg feature for a long
time, so it makes sense to add a test to verify each new feature has
some basic functionality. If the f_random_corruption test is in the
git tree, it would be good to add the flex_bg option to the list of
possible feature combinations to test.
Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.
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