[PATCH 22/25] staging: erofs: introduce workstation for decompression

Gao Xiang
2018-07-26T12:28:45Z

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>
---
drivers/staging/erofs/internal.h | 93 ++++++++++++++++++++++++++++++++++++++++
drivers/staging/erofs/super.c | 9 ++++
drivers/staging/erofs/utils.c | 81 ++++++++++++++++++++++++++++++++--
3 files changed, 180 insertions(+), 3 deletions(-)

diff --git a/drivers/staging/erofs/internal.h b/drivers/staging/erofs/internal.h
index 42455f0..b07cd7a 100644
--- a/drivers/staging/erofs/internal.h
+++ b/drivers/staging/erofs/internal.h
@@ -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

diff --git a/drivers/staging/erofs/super.c b/drivers/staging/erofs/super.c
index ef85884..e155a2b 100644
--- a/drivers/staging/erofs/super.c
+++ b/drivers/staging/erofs/super.c
@@ -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);

diff --git a/drivers/staging/erofs/utils.c b/drivers/staging/erofs/utils.c
index c1d83ce..0d4eae2 100644
--- a/drivers/staging/erofs/utils.c
+++ b/drivers/staging/erofs/utils.c
@@ -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 @@ struct page *erofs_allocpage(struct list_head *pool, gfp_t gfp)
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;
}
--
1.9.1