fs/ext4/ialloc.c

Source file repositories/reference/linux-study-clean/fs/ext4/ialloc.c

File Facts

System
Linux kernel
Corpus path
fs/ext4/ialloc.c
Extension
.c
Size
45758 bytes
Lines
1629
Domain
Core OS
Bucket
VFS And Filesystem Core
Inferred role
Core OS: implementation source
Status
source implementation candidate

Why This File Exists

Core operating-system implementation surface: boot, tasks, memory, VFS, syscall-facing interfaces, synchronization, credentials, and isolation.

Dependency Surface

Detected Declarations

Annotated Snippet

struct orlov_stats {
	__u64 free_clusters;
	__u32 free_inodes;
	__u32 used_dirs;
};

/*
 * Helper function for Orlov's allocator; returns critical information
 * for a particular block group or flex_bg.  If flex_size is 1, then g
 * is a block group number; otherwise it is flex_bg number.
 */
static void get_orlov_stats(struct super_block *sb, ext4_group_t g,
			    int flex_size, struct orlov_stats *stats)
{
	struct ext4_group_desc *desc;

	if (flex_size > 1) {
		struct flex_groups *fg = sbi_array_rcu_deref(EXT4_SB(sb),
							     s_flex_groups, g);
		stats->free_inodes = atomic_read(&fg->free_inodes);
		stats->free_clusters = atomic64_read(&fg->free_clusters);
		stats->used_dirs = atomic_read(&fg->used_dirs);
		return;
	}

	desc = ext4_get_group_desc(sb, g, NULL);
	if (desc) {
		stats->free_inodes = ext4_free_inodes_count(sb, desc);
		stats->free_clusters = ext4_free_group_clusters(sb, desc);
		stats->used_dirs = ext4_used_dirs_count(sb, desc);
	} else {
		stats->free_inodes = 0;
		stats->free_clusters = 0;
		stats->used_dirs = 0;
	}
}

/*
 * Orlov's allocator for directories.
 *
 * We always try to spread first-level directories.
 *
 * If there are blockgroups with both free inodes and free clusters counts
 * not worse than average we return one with smallest directory count.
 * Otherwise we simply return a random group.
 *
 * For the rest rules look so:
 *
 * It's OK to put directory into a group unless
 * it has too many directories already (max_dirs) or
 * it has too few free inodes left (min_inodes) or
 * it has too few free clusters left (min_clusters) or
 * Parent's group is preferred, if it doesn't satisfy these
 * conditions we search cyclically through the rest. If none
 * of the groups look good we just look for a group with more
 * free inodes than average (starting at parent's group).
 */

static int find_group_orlov(struct super_block *sb, struct inode *parent,
			    ext4_group_t *group, umode_t mode,
			    const struct qstr *qstr)
{
	ext4_group_t parent_group = EXT4_I(parent)->i_block_group;
	struct ext4_sb_info *sbi = EXT4_SB(sb);
	ext4_group_t real_ngroups = ext4_get_groups_count(sb);
	int inodes_per_group = EXT4_INODES_PER_GROUP(sb);
	unsigned int freei, avefreei, grp_free;
	ext4_fsblk_t freec, avefreec;
	unsigned int ndirs;
	int max_dirs, min_inodes;
	ext4_grpblk_t min_clusters;
	ext4_group_t i, grp, g, ngroups;
	struct ext4_group_desc *desc;
	struct orlov_stats stats;
	int flex_size = ext4_flex_bg_size(sbi);
	struct dx_hash_info hinfo;

	ngroups = real_ngroups;
	if (flex_size > 1) {
		ngroups = (real_ngroups + flex_size - 1) >>
			sbi->s_log_groups_per_flex;
		parent_group >>= sbi->s_log_groups_per_flex;
	}

	freei = percpu_counter_read_positive(&sbi->s_freeinodes_counter);
	avefreei = freei / ngroups;
	freec = percpu_counter_read_positive(&sbi->s_freeclusters_counter);
	avefreec = freec;
	do_div(avefreec, ngroups);
	ndirs = percpu_counter_read_positive(&sbi->s_dirs_counter);

Annotation

Implementation Notes