f2fs: move f2fs to use reader-unfair rwsems

f2fs rw_semaphores work better if writers can starve readers,
especially for the checkpoint thread, because writers are strictly
more important than reader threads. This prevents significant priority
inversion between low-priority readers that blocked while trying to
acquire the read lock and a second acquisition of the write lock that
might be blocking high priority work.

Signed-off-by: Tim Murray <timmurray@google.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

1 files changed, 89 insertions, 21 deletions

diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index eb22fa91c2b2..8178a9152e49 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -123,6 +123,18 @@ typedef u32 nid_t;
 
 #define COMPRESS_EXT_NUM		16
 
+/*
+ * An implementation of an rwsem that is explicitly unfair to readers. This
+ * prevents priority inversion when a low-priority reader acquires the read lock
+ * while sleeping on the write lock but the write lock is needed by
+ * higher-priority clients.
+ */
+
+struct f2fs_rwsem {
+        struct rw_semaphore internal_rwsem;
+        wait_queue_head_t read_waiters;
+};
+
 struct f2fs_mount_info {
 	unsigned int opt;
 	int write_io_size_bits;		/* Write IO size bits */
@@ -752,7 +764,7 @@ struct f2fs_inode_info {
 
 	/* Use below internally in f2fs*/
 	unsigned long flags[BITS_TO_LONGS(FI_MAX)];	/* use to pass per-file flags */
-	struct rw_semaphore i_sem;	/* protect fi info */
+	struct f2fs_rwsem i_sem;	/* protect fi info */
 	atomic_t dirty_pages;		/* # of dirty pages */
 	f2fs_hash_t chash;		/* hash value of given file name */
 	unsigned int clevel;		/* maximum level of given file name */
@@ -777,8 +789,8 @@ struct f2fs_inode_info {
 	struct extent_tree *extent_tree;	/* cached extent_tree entry */
 
 	/* avoid racing between foreground op and gc */
-	struct rw_semaphore i_gc_rwsem[2];
-	struct rw_semaphore i_xattr_sem; /* avoid racing between reading and changing EAs */
+	struct f2fs_rwsem i_gc_rwsem[2];
+	struct f2fs_rwsem i_xattr_sem; /* avoid racing between reading and changing EAs */
 
 	int i_extra_isize;		/* size of extra space located in i_addr */
 	kprojid_t i_projid;		/* id for project quota */
@@ -904,7 +916,7 @@ struct f2fs_nm_info {
 	/* NAT cache management */
 	struct radix_tree_root nat_root;/* root of the nat entry cache */
 	struct radix_tree_root nat_set_root;/* root of the nat set cache */
-	struct rw_semaphore nat_tree_lock;	/* protect nat entry tree */
+	struct f2fs_rwsem nat_tree_lock;	/* protect nat entry tree */
 	struct list_head nat_entries;	/* cached nat entry list (clean) */
 	spinlock_t nat_list_lock;	/* protect clean nat entry list */
 	unsigned int nat_cnt[MAX_NAT_STATE]; /* the # of cached nat entries */
@@ -1017,7 +1029,7 @@ struct f2fs_sm_info {
 	struct dirty_seglist_info *dirty_info;	/* dirty segment information */
 	struct curseg_info *curseg_array;	/* active segment information */
 
-	struct rw_semaphore curseg_lock;	/* for preventing curseg change */
+	struct f2fs_rwsem curseg_lock;	/* for preventing curseg change */
 
 	block_t seg0_blkaddr;		/* block address of 0'th segment */
 	block_t main_blkaddr;		/* start block address of main area */
@@ -1201,11 +1213,11 @@ struct f2fs_bio_info {
 	struct bio *bio;		/* bios to merge */
 	sector_t last_block_in_bio;	/* last block number */
 	struct f2fs_io_info fio;	/* store buffered io info. */
-	struct rw_semaphore io_rwsem;	/* blocking op for bio */
+	struct f2fs_rwsem io_rwsem;	/* blocking op for bio */
 	spinlock_t io_lock;		/* serialize DATA/NODE IOs */
 	struct list_head io_list;	/* track fios */
 	struct list_head bio_list;	/* bio entry list head */
-	struct rw_semaphore bio_list_lock;	/* lock to protect bio entry list */
+	struct f2fs_rwsem bio_list_lock;	/* lock to protect bio entry list */
 };
 
 #define FDEV(i)				(sbi->devs[i])
@@ -1571,7 +1583,7 @@ struct f2fs_sb_info {
 	struct super_block *sb;			/* pointer to VFS super block */
 	struct proc_dir_entry *s_proc;		/* proc entry */
 	struct f2fs_super_block *raw_super;	/* raw super block pointer */
-	struct rw_semaphore sb_lock;		/* lock for raw super block */
+	struct f2fs_rwsem sb_lock;		/* lock for raw super block */
 	int valid_super_block;			/* valid super block no */
 	unsigned long s_flag;				/* flags for sbi */
 	struct mutex writepages;		/* mutex for writepages() */
@@ -1591,7 +1603,7 @@ struct f2fs_sb_info {
 	/* for bio operations */
 	struct f2fs_bio_info *write_io[NR_PAGE_TYPE];	/* for write bios */
 	/* keep migration IO order for LFS mode */
-	struct rw_semaphore io_order_lock;
+	struct f2fs_rwsem io_order_lock;
 	mempool_t *write_io_dummy;		/* Dummy pages */
 
 	/* for checkpoint */
@@ -1599,10 +1611,10 @@ struct f2fs_sb_info {
 	int cur_cp_pack;			/* remain current cp pack */
 	spinlock_t cp_lock;			/* for flag in ckpt */
 	struct inode *meta_inode;		/* cache meta blocks */
-	struct rw_semaphore cp_global_sem;	/* checkpoint procedure lock */
-	struct rw_semaphore cp_rwsem;		/* blocking FS operations */
-	struct rw_semaphore node_write;		/* locking node writes */
-	struct rw_semaphore node_change;	/* locking node change */
+	struct f2fs_rwsem cp_global_sem;	/* checkpoint procedure lock */
+	struct f2fs_rwsem cp_rwsem;		/* blocking FS operations */
+	struct f2fs_rwsem node_write;		/* locking node writes */
+	struct f2fs_rwsem node_change;	/* locking node change */
 	wait_queue_head_t cp_wait;
 	unsigned long last_time[MAX_TIME];	/* to store time in jiffies */
 	long interval_time[MAX_TIME];		/* to store thresholds */
@@ -1662,7 +1674,7 @@ struct f2fs_sb_info {
 	block_t unusable_block_count;		/* # of blocks saved by last cp */
 
 	unsigned int nquota_files;		/* # of quota sysfile */
-	struct rw_semaphore quota_sem;		/* blocking cp for flags */
+	struct f2fs_rwsem quota_sem;		/* blocking cp for flags */
 
 	/* # of pages, see count_type */
 	atomic_t nr_pages[NR_COUNT_TYPE];
@@ -1678,7 +1690,7 @@ struct f2fs_sb_info {
 	struct f2fs_mount_info mount_opt;	/* mount options */
 
 	/* for cleaning operations */
-	struct rw_semaphore gc_lock;		/*
+	struct f2fs_rwsem gc_lock;		/*
 						 * semaphore for GC, avoid
 						 * race between GC and GC or CP
 						 */
@@ -1698,7 +1710,7 @@ struct f2fs_sb_info {
 
 	/* threshold for gc trials on pinned files */
 	u64 gc_pin_file_threshold;
-	struct rw_semaphore pin_sem;
+	struct f2fs_rwsem pin_sem;
 
 	/* maximum # of trials to find a victim segment for SSR and GC */
 	unsigned int max_victim_search;
@@ -2092,9 +2104,65 @@ static inline void clear_ckpt_flags(struct f2fs_sb_info *sbi, unsigned int f)
 	spin_unlock_irqrestore(&sbi->cp_lock, flags);
 }
 
+static inline void init_f2fs_rwsem(struct f2fs_rwsem *sem)
+{
+	init_rwsem(&sem->internal_rwsem);
+	init_waitqueue_head(&sem->read_waiters);
+}
+
+static inline int f2fs_rwsem_is_locked(struct f2fs_rwsem *sem)
+{
+	return rwsem_is_locked(&sem->internal_rwsem);
+}
+
+static inline int f2fs_rwsem_is_contended(struct f2fs_rwsem *sem)
+{
+	return rwsem_is_contended(&sem->internal_rwsem);
+}
+
+static inline void f2fs_down_read(struct f2fs_rwsem *sem)
+{
+	wait_event(sem->read_waiters, down_read_trylock(&sem->internal_rwsem));
+}
+
+static inline int f2fs_down_read_trylock(struct f2fs_rwsem *sem)
+{
+	return down_read_trylock(&sem->internal_rwsem);
+}
+
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+static inline void f2fs_down_read_nested(struct f2fs_rwsem *sem, int subclass)
+{
+	down_read_nested(&sem->internal_rwsem, subclass);
+}
+#else
+#define f2fs_down_read_nested(sem, subclass) f2fs_down_read(sem)
+#endif
+
+static inline void f2fs_up_read(struct f2fs_rwsem *sem)
+{
+	up_read(&sem->internal_rwsem);
+}
+
+static inline void f2fs_down_write(struct f2fs_rwsem *sem)
+{
+	down_write(&sem->internal_rwsem);
+}
+
+static inline int f2fs_down_write_trylock(struct f2fs_rwsem *sem)
+{
+	return down_write_trylock(&sem->internal_rwsem);
+}
+
+static inline void f2fs_up_write(struct f2fs_rwsem *sem)
+{
+	up_write(&sem->internal_rwsem);
+	wake_up_all(&sem->read_waiters);
+}
+
 static inline void f2fs_lock_op(struct f2fs_sb_info *sbi)
 {
-	down_read(&sbi->cp_rwsem);
+	f2fs_down_read(&sbi->cp_rwsem);
 }
 
 static inline int f2fs_trylock_op(struct f2fs_sb_info *sbi)
@@ -2103,22 +2171,22 @@ static inline int f2fs_trylock_op(struct f2fs_sb_info *sbi)
 		f2fs_show_injection_info(sbi, FAULT_LOCK_OP);
 		return 0;
 	}
-	return down_read_trylock(&sbi->cp_rwsem);
+	return f2fs_down_read_trylock(&sbi->cp_rwsem);
 }
 
 static inline void f2fs_unlock_op(struct f2fs_sb_info *sbi)
 {
-	up_read(&sbi->cp_rwsem);
+	f2fs_up_read(&sbi->cp_rwsem);
 }
 
 static inline void f2fs_lock_all(struct f2fs_sb_info *sbi)
 {
-	down_write(&sbi->cp_rwsem);
+	f2fs_down_write(&sbi->cp_rwsem);
 }
 
 static inline void f2fs_unlock_all(struct f2fs_sb_info *sbi)
 {
-	up_write(&sbi->cp_rwsem);
+	f2fs_up_write(&sbi->cp_rwsem);
 }
 
 static inline int __get_cp_reason(struct f2fs_sb_info *sbi)