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staging: erofs: introduce workstation for decompression

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This patch introduces another concept used by the unzip
subsystem called 'workstation'. It can be seen as a sparse
array that stores pointers pointed to data structures
related to the corresponding physical blocks.

All lookup cases are protected by RCU read lock. Besides,
reference count and spin_lock are also introduced to
manage its lifetime and serialize all update operations.

'workstation' is currently implemented on the in-kernel
radix tree approach for backward compatibility.
With the evolution of linux kernel, it could be migrated
into XArray implementation in the future.

Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Gao Xiang 2018-07-26 20:22:05 +08:00 committed by Greg Kroah-Hartman
parent a158131262
commit e7e9a307be
3 changed files with 180 additions and 3 deletions
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93
drivers/staging/erofs/internal.h
View File

@ -79,6 +79,9 @@ struct erofs_sb_info {
#ifdef CONFIG_EROFS_FS_ZIP
/* cluster size in bit shift */
unsigned char clusterbits;
/* the dedicated workstation for compression */
struct radix_tree_root workstn_tree;
#endif
u32 build_time_nsec;
@ -149,6 +152,96 @@ static inline void *erofs_kmalloc(struct erofs_sb_info *sbi,
#define set_opt(sbi, option) ((sbi)->mount_opt |= EROFS_MOUNT_##option)
#define test_opt(sbi, option) ((sbi)->mount_opt & EROFS_MOUNT_##option)
#ifdef CONFIG_EROFS_FS_ZIP
#define erofs_workstn_lock(sbi) xa_lock(&(sbi)->workstn_tree)
#define erofs_workstn_unlock(sbi) xa_unlock(&(sbi)->workstn_tree)
/* basic unit of the workstation of a super_block */
struct erofs_workgroup {
/* the workgroup index in the workstation */
pgoff_t index;
/* overall workgroup reference count */
atomic_t refcount;
};
#define EROFS_LOCKED_MAGIC (INT_MIN | 0xE0F510CCL)
static inline bool erofs_workgroup_try_to_freeze(
struct erofs_workgroup *grp, int v)
{
#if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)
if (v != atomic_cmpxchg(&grp->refcount,
v, EROFS_LOCKED_MAGIC))
return false;
preempt_disable();
#else
preempt_disable();
if (atomic_read(&grp->refcount) != v) {
preempt_enable();
return false;
}
#endif
return true;
}
static inline void erofs_workgroup_unfreeze(
struct erofs_workgroup *grp, int v)
{
#if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)
atomic_set(&grp->refcount, v);
#endif
preempt_enable();
}
static inline bool erofs_workgroup_get(struct erofs_workgroup *grp, int *ocnt)
{
const int locked = (int)EROFS_LOCKED_MAGIC;
int o;
repeat:
o = atomic_read(&grp->refcount);
/* spin if it is temporarily locked at the reclaim path */
if (unlikely(o == locked)) {
#if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)
do
cpu_relax();
while (atomic_read(&grp->refcount) == locked);
#endif
goto repeat;
}
if (unlikely(o <= 0))
return -1;
if (unlikely(atomic_cmpxchg(&grp->refcount, o, o + 1) != o))
goto repeat;
*ocnt = o;
return 0;
}
#define __erofs_workgroup_get(grp) atomic_inc(&(grp)->refcount)
extern int erofs_workgroup_put(struct erofs_workgroup *grp);
extern struct erofs_workgroup *erofs_find_workgroup(
struct super_block *sb, pgoff_t index, bool *tag);
extern int erofs_register_workgroup(struct super_block *sb,
struct erofs_workgroup *grp, bool tag);
extern unsigned long erofs_shrink_workstation(struct erofs_sb_info *sbi,
unsigned long nr_shrink, bool cleanup);
static inline void erofs_workstation_cleanup_all(struct super_block *sb)
{
erofs_shrink_workstation(EROFS_SB(sb), ~0UL, true);
}
#endif
/* we strictly follow PAGE_SIZE and no buffer head yet */
#define LOG_BLOCK_SIZE PAGE_SHIFT

9
drivers/staging/erofs/super.c
View File

@ -296,6 +296,10 @@ static int erofs_read_super(struct super_block *sb,
if (!silent)
infoln("root inode @ nid %llu", ROOT_NID(sbi));
#ifdef CONFIG_EROFS_FS_ZIP
INIT_RADIX_TREE(&sbi->workstn_tree, GFP_ATOMIC);
#endif
/* get the root inode */
inode = erofs_iget(sb, ROOT_NID(sbi), true);
if (IS_ERR(inode)) {
@ -376,6 +380,11 @@ static void erofs_put_super(struct super_block *sb)
__putname(sbi->dev_name);
mutex_lock(&sbi->umount_mutex);
#ifdef CONFIG_EROFS_FS_ZIP
erofs_workstation_cleanup_all(sb);
#endif
erofs_unregister_super(sb);
mutex_unlock(&sbi->umount_mutex);

81
drivers/staging/erofs/utils.c
View File

@ -29,6 +29,83 @@ struct page *erofs_allocpage(struct list_head *pool, gfp_t gfp)
return page;
}
/* global shrink count (for all mounted EROFS instances) */
static atomic_long_t erofs_global_shrink_cnt;
#ifdef CONFIG_EROFS_FS_ZIP
/* radix_tree and the future XArray both don't use tagptr_t yet */
struct erofs_workgroup *erofs_find_workgroup(
struct super_block *sb, pgoff_t index, bool *tag)
{
struct erofs_sb_info *sbi = EROFS_SB(sb);
struct erofs_workgroup *grp;
int oldcount;
repeat:
rcu_read_lock();
grp = radix_tree_lookup(&sbi->workstn_tree, index);
if (grp != NULL) {
*tag = radix_tree_exceptional_entry(grp);
grp = (void *)((unsigned long)grp &
~RADIX_TREE_EXCEPTIONAL_ENTRY);
if (erofs_workgroup_get(grp, &oldcount)) {
/* prefer to relax rcu read side */
rcu_read_unlock();
goto repeat;
}
/* decrease refcount added by erofs_workgroup_put */
if (unlikely(oldcount == 1))
atomic_long_dec(&erofs_global_shrink_cnt);
BUG_ON(index != grp->index);
}
rcu_read_unlock();
return grp;
}
int erofs_register_workgroup(struct super_block *sb,
struct erofs_workgroup *grp,
bool tag)
{
struct erofs_sb_info *sbi;
int err;
/* grp->refcount should not < 1 */
BUG_ON(!atomic_read(&grp->refcount));
err = radix_tree_preload(GFP_NOFS);
if (err)
return err;
sbi = EROFS_SB(sb);
erofs_workstn_lock(sbi);
if (tag)
grp = (void *)((unsigned long)grp |
1UL << RADIX_TREE_EXCEPTIONAL_SHIFT);
err = radix_tree_insert(&sbi->workstn_tree,
grp->index, grp);
if (!err) {
__erofs_workgroup_get(grp);
}
erofs_workstn_unlock(sbi);
radix_tree_preload_end();
return err;
}
unsigned long erofs_shrink_workstation(struct erofs_sb_info *sbi,
unsigned long nr_shrink,
bool cleanup)
{
return 0;
}
#endif
/* protected by 'erofs_sb_list_lock' */
static unsigned int shrinker_run_no;
@ -37,9 +114,6 @@ static unsigned int shrinker_run_no;
static DEFINE_SPINLOCK(erofs_sb_list_lock);
static LIST_HEAD(erofs_sb_list);
/* global shrink count (for all mounted EROFS instances) */
static atomic_long_t erofs_global_shrink_cnt;
void erofs_register_super(struct super_block *sb)
{
struct erofs_sb_info *sbi = EROFS_SB(sb);
@ -112,6 +186,7 @@ unsigned long erofs_shrink_scan(struct shrinker *shrink,
list_move_tail(&sbi->list, &erofs_sb_list);
mutex_unlock(&sbi->umount_mutex);
freed += erofs_shrink_workstation(sbi, nr, false);
if (freed >= nr)
break;
}