[PATCH 21/25] staging: erofs: introduce erofs shrinker

Gao Xiang
2018-07-26T12:28:30Z

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 scaned objects

Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>
---
drivers/staging/erofs/internal.h | 7 ++++
drivers/staging/erofs/super.c | 15 +++++++
drivers/staging/erofs/utils.c | 85 +++++++++++++++++++++++++++++++++++++---
3 files changed, 101 insertions(+), 6 deletions(-)

diff --git a/drivers/staging/erofs/internal.h b/drivers/staging/erofs/internal.h
index 18e7b9c..42455f0 100644
--- a/drivers/staging/erofs/internal.h
+++ b/drivers/staging/erofs/internal.h
@@ -66,6 +66,7 @@ struct erofs_fault_info {
struct erofs_sb_info {
/* list for all registered superblocks, mainly for shrinker */
struct list_head list;
+ struct mutex umount_mutex;

u32 blocks;
u32 meta_blkaddr;
@@ -93,6 +94,7 @@ struct erofs_sb_info {
char *dev_name;

unsigned int mount_opt;
+ unsigned int shrinker_run_no;

#ifdef CONFIG_EROFS_FAULT_INJECTION
struct erofs_fault_info fault_info; /* For fault injection */
@@ -416,6 +418,11 @@ static inline void erofs_vunmap(const void *mem, unsigned int count)
extern void erofs_register_super(struct super_block *sb);
extern void erofs_unregister_super(struct super_block *sb);

+extern unsigned long erofs_shrink_count(struct shrinker *shrink,
+ struct shrink_control *sc);
+extern unsigned long erofs_shrink_scan(struct shrinker *shrink,
+ struct shrink_control *sc);
+
#ifndef lru_to_page
#define lru_to_page(head) (list_entry((head)->prev, struct page, lru))
#endif
diff --git a/drivers/staging/erofs/super.c b/drivers/staging/erofs/super.c
index f455d71..ef85884 100644
--- a/drivers/staging/erofs/super.c
+++ b/drivers/staging/erofs/super.c
@@ -375,7 +375,9 @@ static void erofs_put_super(struct super_block *sb)
infoln("unmounted for %s", sbi->dev_name);
__putname(sbi->dev_name);

+ mutex_lock(&sbi->umount_mutex);
erofs_unregister_super(sb);
+ mutex_unlock(&sbi->umount_mutex);

kfree(sbi);
sb->s_fs_info = NULL;
@@ -415,6 +417,12 @@ static void erofs_kill_sb(struct super_block *sb)
kill_block_super(sb);
}

+static struct shrinker erofs_shrinker_info = {
+ .scan_objects = erofs_shrink_scan,
+ .count_objects = erofs_shrink_count,
+ .seeks = DEFAULT_SEEKS,
+};
+
static struct file_system_type erofs_fs_type = {
.owner = THIS_MODULE,
.name = "erofs",
@@ -435,6 +443,10 @@ static int __init erofs_module_init(void)
if (err)
goto icache_err;

+ err = register_shrinker(&erofs_shrinker_info);
+ if (err)
+ goto shrinker_err;
+
err = register_filesystem(&erofs_fs_type);
if (err)
goto fs_err;
@@ -443,6 +455,8 @@ static int __init erofs_module_init(void)
return 0;

fs_err:
+ unregister_shrinker(&erofs_shrinker_info);
+shrinker_err:
erofs_exit_inode_cache();
icache_err:
return err;
@@ -451,6 +465,7 @@ static int __init erofs_module_init(void)
static void __exit erofs_module_exit(void)
{
unregister_filesystem(&erofs_fs_type);
+ unregister_shrinker(&erofs_shrinker_info);
erofs_exit_inode_cache();
infoln("successfully finalize erofs");
}
diff --git a/drivers/staging/erofs/utils.c b/drivers/staging/erofs/utils.c
index 6748def..c1d83ce 100644
--- a/drivers/staging/erofs/utils.c
+++ b/drivers/staging/erofs/utils.c
@@ -29,20 +29,93 @@ struct page *erofs_allocpage(struct list_head *pool, gfp_t gfp)
return page;
}

-static DEFINE_MUTEX(erofs_sb_list_lock);
+
+/* 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);

+/* global shrink count (for all mounted EROFS instances) */
+static atomic_long_t erofs_global_shrink_cnt;
+
void erofs_register_super(struct super_block *sb)
{
- mutex_lock(&erofs_sb_list_lock);
- list_add(&EROFS_SB(sb)->list, &erofs_sb_list);
- mutex_unlock(&erofs_sb_list_lock);
+ 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);
}

void erofs_unregister_super(struct super_block *sb)
{
- mutex_lock(&erofs_sb_list_lock);
+ spin_lock(&erofs_sb_list_lock);
list_del(&EROFS_SB(sb)->list);
- mutex_unlock(&erofs_sb_list_lock);
+ spin_unlock(&erofs_sb_list_lock);
+}
+
+unsigned long erofs_shrink_count(struct shrinker *shrink,
+ struct shrink_control *sc)
+{
+ return atomic_long_read(&erofs_global_shrink_cnt);
+}
+
+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);
+ 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;
+
+ /* add scan handlers 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;
}

--
1.9.1