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Subject[PATCH v7 15/24] erofs: introduce erofs shrinker
Date
This patch adds a dedicated shrinker targeting to free
unneeded memory consumed by a number of erofs in-memory
data structures.

Like F2FS and UBIFS, it also adds:
- sbi->umount_mutex to avoid races on shrinker and put_super;
- sbi->shrinker_run_no to not revisit recently scanned objects.

Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>
---
fs/erofs/internal.h | 7 ++++
fs/erofs/super.c | 6 +++
fs/erofs/utils.c | 93 ++++++++++++++++++++++++++++++++++++++++++++-
3 files changed, 105 insertions(+), 1 deletion(-)

diff --git a/fs/erofs/internal.h b/fs/erofs/internal.h
index 60cc77b42b19..6272793329cd 100644
--- a/fs/erofs/internal.h
+++ b/fs/erofs/internal.h
@@ -63,6 +63,9 @@ struct erofs_sb_info {
#ifdef CONFIG_EROFS_FS_ZIP
/* list for all registered superblocks, mainly for shrinker */
struct list_head list;
+ struct mutex umount_mutex;
+
+ unsigned int shrinker_run_no;
#endif /* CONFIG_EROFS_FS_ZIP */
u32 blocks;
u32 meta_blkaddr;
@@ -408,9 +411,13 @@ extern const struct file_operations erofs_dir_fops;
#ifdef CONFIG_EROFS_FS_ZIP
void erofs_shrinker_register(struct super_block *sb);
void erofs_shrinker_unregister(struct super_block *sb);
+int __init erofs_init_shrinker(void);
+void erofs_exit_shrinker(void);
#else
static inline void erofs_shrinker_register(struct super_block *sb) {}
static inline void erofs_shrinker_unregister(struct super_block *sb) {}
+static inline int erofs_init_shrinker(void) { return 0; }
+static inline void erofs_exit_shrinker(void) {}
#endif /* !CONFIG_EROFS_FS_ZIP */

#endif /* __EROFS_INTERNAL_H */
diff --git a/fs/erofs/super.c b/fs/erofs/super.c
index 2eca3b25db75..09992cc3b2fd 100644
--- a/fs/erofs/super.c
+++ b/fs/erofs/super.c
@@ -413,6 +413,9 @@ static int __init erofs_module_init(void)
if (err)
goto icache_err;

+ err = erofs_init_shrinker();
+ if (err)
+ goto shrinker_err;
err = register_filesystem(&erofs_fs_type);
if (err)
goto fs_err;
@@ -421,6 +424,8 @@ static int __init erofs_module_init(void)
return 0;

fs_err:
+ erofs_exit_shrinker();
+shrinker_err:
erofs_exit_inode_cache();
icache_err:
return err;
@@ -429,6 +434,7 @@ static int __init erofs_module_init(void)
static void __exit erofs_module_exit(void)
{
unregister_filesystem(&erofs_fs_type);
+ erofs_exit_shrinker();
erofs_exit_inode_cache();
infoln("successfully finalize erofs");
}
diff --git a/fs/erofs/utils.c b/fs/erofs/utils.c
index 791b2df1f761..cab7d77c4e59 100644
--- a/fs/erofs/utils.c
+++ b/fs/erofs/utils.c
@@ -9,6 +9,12 @@
#include "internal.h"

#ifdef CONFIG_EROFS_FS_ZIP
+/* global shrink count (for all mounted EROFS instances) */
+static atomic_long_t erofs_global_shrink_cnt;
+
+/* protected by 'erofs_sb_list_lock' */
+static unsigned int shrinker_run_no;
+
/* protects the mounted 'erofs_sb_list' */
static DEFINE_SPINLOCK(erofs_sb_list_lock);
static LIST_HEAD(erofs_sb_list);
@@ -17,6 +23,8 @@ void erofs_shrinker_register(struct super_block *sb)
{
struct erofs_sb_info *sbi = EROFS_SB(sb);

+ mutex_init(&sbi->umount_mutex);
+
spin_lock(&erofs_sb_list_lock);
list_add(&sbi->list, &erofs_sb_list);
spin_unlock(&erofs_sb_list_lock);
@@ -24,9 +32,92 @@ void erofs_shrinker_register(struct super_block *sb)

void erofs_shrinker_unregister(struct super_block *sb)
{
+ struct erofs_sb_info *const sbi = EROFS_SB(sb);
+
+ mutex_lock(&sbi->umount_mutex);
+ /* will add shrink final handler here */
+
+ spin_lock(&erofs_sb_list_lock);
+ list_del(&sbi->list);
+ spin_unlock(&erofs_sb_list_lock);
+ mutex_unlock(&sbi->umount_mutex);
+}
+
+static unsigned long erofs_shrink_count(struct shrinker *shrink,
+ struct shrink_control *sc)
+{
+ return atomic_long_read(&erofs_global_shrink_cnt);
+}
+
+static unsigned long erofs_shrink_scan(struct shrinker *shrink,
+ struct shrink_control *sc)
+{
+ struct erofs_sb_info *sbi;
+ struct list_head *p;
+
+ unsigned long nr = sc->nr_to_scan;
+ unsigned int run_no;
+ unsigned long freed = 0;
+
spin_lock(&erofs_sb_list_lock);
- list_del(&EROFS_SB(sb)->list);
+ do {
+ run_no = ++shrinker_run_no;
+ } while (run_no == 0);
+
+ /* Iterate over all mounted superblocks and try to shrink them */
+ p = erofs_sb_list.next;
+ while (p != &erofs_sb_list) {
+ sbi = list_entry(p, struct erofs_sb_info, list);
+
+ /*
+ * We move the ones we do to the end of the list, so we stop
+ * when we see one we have already done.
+ */
+ if (sbi->shrinker_run_no == run_no)
+ break;
+
+ if (!mutex_trylock(&sbi->umount_mutex)) {
+ p = p->next;
+ continue;
+ }
+
+ spin_unlock(&erofs_sb_list_lock);
+ sbi->shrinker_run_no = run_no;
+
+ /* will add shrink handler here */
+
+ spin_lock(&erofs_sb_list_lock);
+ /* Get the next list element before we move this one */
+ p = p->next;
+
+ /*
+ * Move this one to the end of the list to provide some
+ * fairness.
+ */
+ list_move_tail(&sbi->list, &erofs_sb_list);
+ mutex_unlock(&sbi->umount_mutex);
+
+ if (freed >= nr)
+ break;
+ }
spin_unlock(&erofs_sb_list_lock);
+ return freed;
+}
+
+static struct shrinker erofs_shrinker_info = {
+ .scan_objects = erofs_shrink_scan,
+ .count_objects = erofs_shrink_count,
+ .seeks = DEFAULT_SEEKS,
+};
+
+int __init erofs_init_shrinker(void)
+{
+ return register_shrinker(&erofs_shrinker_info);
+}
+
+void erofs_exit_shrinker(void)
+{
+ unregister_shrinker(&erofs_shrinker_info);
}
#endif /* !CONFIG_EROFS_FS_ZIP */

--
2.17.1
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