f2fs: introduce f2fs_issue_flush to avoid redundant flush issue

Some storage devices show relatively high latencies to complete cache_flush
commands, even though their normal IO speed is prettry much high. In such
the case, it needs to merge cache_flush commands as much as possible to avoid
issuing them redundantly.
So, this patch introduces a mount option, "-o flush_merge", to mitigate such
the overhead.

If this option is enabled by user, F2FS merges the cache_flush commands and then
issues just one cache_flush on behalf of them. Once the single command is
finished, F2FS sends a completion signal to all the pending threads.

Note that, this option can be used under a workload consisting of very intensive
concurrent fsync calls, while the storage handles cache_flush commands slowly.

Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>

diff --git a/Documentation/filesystems/f2fs.txt b/Documentation/filesystems/f2fs.txt
index 2f6d021..25311e1 100644 (file)
--- a/Documentation/filesystems/f2fs.txt
+++ b/Documentation/filesystems/f2fs.txt
@@ -122,6 +122,10 @@ disable_ext_identify   Disable the extension list configured by mkfs, so f2fs
 inline_xattr           Enable the inline xattrs feature.
 inline_data            Enable the inline data feature: New created small(<~3.4k)
                        files can be written into inode block.
+flush_merge           Merge concurrent cache_flush commands as much as possible
+                       to eliminate redundant command issues. If the underlying
+                      device handles the cache_flush command relatively slowly,
+                      recommend to enable this option.
 
 ================================================================================
 DEBUGFS ENTRIES

diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index 1e3d869..2ecac83 100644 (file)
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -40,6 +40,7 @@
 #define F2FS_MOUNT_DISABLE_EXT_IDENTIFY        0x00000040
 #define F2FS_MOUNT_INLINE_XATTR                0x00000080
 #define F2FS_MOUNT_INLINE_DATA         0x00000100
+#define F2FS_MOUNT_FLUSH_MERGE         0x00000200
 
 #define clear_opt(sbi, option) (sbi->mount_opt.opt &= ~F2FS_MOUNT_##option)
 #define set_opt(sbi, option)   (sbi->mount_opt.opt |= F2FS_MOUNT_##option)
@@ -316,6 +317,12 @@ enum {
        NO_CHECK_TYPE
 };
 
+struct flush_cmd {
+       struct flush_cmd *next;
+       struct completion wait;
+       int ret;
+};
+
 struct f2fs_sm_info {
        struct sit_info *sit_info;              /* whole segment information */
        struct free_segmap_info *free_info;     /* free segment information */
@@ -344,6 +351,14 @@ struct f2fs_sm_info {
 
        unsigned int ipu_policy;        /* in-place-update policy */
        unsigned int min_ipu_util;      /* in-place-update threshold */
+
+       /* for flush command control */
+       struct task_struct *f2fs_issue_flush;   /* flush thread */
+       wait_queue_head_t flush_wait_queue;     /* waiting queue for wake-up */
+       struct flush_cmd *issue_list;           /* list for command issue */
+       struct flush_cmd *dispatch_list;        /* list for command dispatch */
+       spinlock_t issue_lock;                  /* for issue list lock */
+       struct flush_cmd *issue_tail;           /* list tail of issue list */
 };
 
 /*
@@ -1160,6 +1175,7 @@ void destroy_node_manager_caches(void);
  */
 void f2fs_balance_fs(struct f2fs_sb_info *);
 void f2fs_balance_fs_bg(struct f2fs_sb_info *);
+int f2fs_issue_flush(struct f2fs_sb_info *);
 void invalidate_blocks(struct f2fs_sb_info *, block_t);
 void refresh_sit_entry(struct f2fs_sb_info *, block_t, block_t);
 void clear_prefree_segments(struct f2fs_sb_info *);

diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index 6ba2668..302d552 100644 (file)
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -186,7 +186,7 @@ int f2fs_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
                ret = wait_on_node_pages_writeback(sbi, inode->i_ino);
                if (ret)
                        goto out;
-               ret = blkdev_issue_flush(inode->i_sb->s_bdev, GFP_KERNEL, NULL);
+               ret = f2fs_issue_flush(F2FS_SB(inode->i_sb));
        }
 out:
        trace_f2fs_sync_file_exit(inode, need_cp, datasync, ret);

diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index f799c6a..085f548 100644 (file)
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -13,6 +13,7 @@
 #include <linux/bio.h>
 #include <linux/blkdev.h>
 #include <linux/prefetch.h>
+#include <linux/kthread.h>
 #include <linux/vmalloc.h>
 #include <linux/swap.h>
 
@@ -24,6 +25,7 @@
 #define __reverse_ffz(x) __reverse_ffs(~(x))
 
 static struct kmem_cache *discard_entry_slab;
+static struct kmem_cache *flush_cmd_slab;
 
 /*
  * __reverse_ffs is copied from include/asm-generic/bitops/__ffs.h since
@@ -195,6 +197,73 @@ void f2fs_balance_fs_bg(struct f2fs_sb_info *sbi)
                f2fs_sync_fs(sbi->sb, true);
 }
 
+static int issue_flush_thread(void *data)
+{
+       struct f2fs_sb_info *sbi = data;
+       struct f2fs_sm_info *sm_i = SM_I(sbi);
+       wait_queue_head_t *q = &sm_i->flush_wait_queue;
+repeat:
+       if (kthread_should_stop())
+               return 0;
+
+       spin_lock(&sm_i->issue_lock);
+       if (sm_i->issue_list) {
+               sm_i->dispatch_list = sm_i->issue_list;
+               sm_i->issue_list = sm_i->issue_tail = NULL;
+       }
+       spin_unlock(&sm_i->issue_lock);
+
+       if (sm_i->dispatch_list) {
+               struct bio *bio = bio_alloc(GFP_NOIO, 0);
+               struct flush_cmd *cmd, *next;
+               int ret;
+
+               bio->bi_bdev = sbi->sb->s_bdev;
+               ret = submit_bio_wait(WRITE_FLUSH, bio);
+
+               for (cmd = sm_i->dispatch_list; cmd; cmd = next) {
+                       cmd->ret = ret;
+                       next = cmd->next;
+                       complete(&cmd->wait);
+               }
+               sm_i->dispatch_list = NULL;
+       }
+
+       wait_event_interruptible(*q, kthread_should_stop() || sm_i->issue_list);
+       goto repeat;
+}
+
+int f2fs_issue_flush(struct f2fs_sb_info *sbi)
+{
+       struct f2fs_sm_info *sm_i = SM_I(sbi);
+       struct flush_cmd *cmd;
+       int ret;
+
+       if (!test_opt(sbi, FLUSH_MERGE))
+               return blkdev_issue_flush(sbi->sb->s_bdev, GFP_KERNEL, NULL);
+
+       cmd = f2fs_kmem_cache_alloc(flush_cmd_slab, GFP_ATOMIC);
+       cmd->next = NULL;
+       cmd->ret = 0;
+       init_completion(&cmd->wait);
+
+       spin_lock(&sm_i->issue_lock);
+       if (sm_i->issue_list)
+               sm_i->issue_tail->next = cmd;
+       else
+               sm_i->issue_list = cmd;
+       sm_i->issue_tail = cmd;
+       spin_unlock(&sm_i->issue_lock);
+
+       if (!sm_i->dispatch_list)
+               wake_up(&sm_i->flush_wait_queue);
+
+       wait_for_completion(&cmd->wait);
+       ret = cmd->ret;
+       kmem_cache_free(flush_cmd_slab, cmd);
+       return ret;
+}
+
 static void __locate_dirty_segment(struct f2fs_sb_info *sbi, unsigned int segno,
                enum dirty_type dirty_type)
 {
@@ -1763,6 +1832,7 @@ int build_segment_manager(struct f2fs_sb_info *sbi)
 {
        struct f2fs_super_block *raw_super = F2FS_RAW_SUPER(sbi);
        struct f2fs_checkpoint *ckpt = F2FS_CKPT(sbi);
+       dev_t dev = sbi->sb->s_bdev->bd_dev;
        struct f2fs_sm_info *sm_info;
        int err;
 
@@ -1790,6 +1860,16 @@ int build_segment_manager(struct f2fs_sb_info *sbi)
        sm_info->nr_discards = 0;
        sm_info->max_discards = 0;
 
+       if (test_opt(sbi, FLUSH_MERGE)) {
+               spin_lock_init(&sm_info->issue_lock);
+               init_waitqueue_head(&sm_info->flush_wait_queue);
+
+               sm_info->f2fs_issue_flush = kthread_run(issue_flush_thread, sbi,
+                               "f2fs_flush-%u:%u", MAJOR(dev), MINOR(dev));
+               if (IS_ERR(sm_info->f2fs_issue_flush))
+                       return PTR_ERR(sm_info->f2fs_issue_flush);
+       }
+
        err = build_sit_info(sbi);
        if (err)
                return err;
@@ -1898,6 +1978,8 @@ void destroy_segment_manager(struct f2fs_sb_info *sbi)
        struct f2fs_sm_info *sm_info = SM_I(sbi);
        if (!sm_info)
                return;
+       if (sm_info->f2fs_issue_flush)
+               kthread_stop(sm_info->f2fs_issue_flush);
        destroy_dirty_segmap(sbi);
        destroy_curseg(sbi);
        destroy_free_segmap(sbi);
@@ -1912,10 +1994,17 @@ int __init create_segment_manager_caches(void)
                        sizeof(struct discard_entry));
        if (!discard_entry_slab)
                return -ENOMEM;
+       flush_cmd_slab = f2fs_kmem_cache_create("flush_command",
+                       sizeof(struct flush_cmd));
+       if (!flush_cmd_slab) {
+               kmem_cache_destroy(discard_entry_slab);
+               return -ENOMEM;
+       }
        return 0;
 }
 
 void destroy_segment_manager_caches(void)
 {
        kmem_cache_destroy(discard_entry_slab);
+       kmem_cache_destroy(flush_cmd_slab);
 }

diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
index 9598340..d31b767 100644 (file)
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -51,6 +51,7 @@ enum {
        Opt_disable_ext_identify,
        Opt_inline_xattr,
        Opt_inline_data,
+       Opt_flush_merge,
        Opt_err,
 };
 
@@ -67,6 +68,7 @@ static match_table_t f2fs_tokens = {
        {Opt_disable_ext_identify, "disable_ext_identify"},
        {Opt_inline_xattr, "inline_xattr"},
        {Opt_inline_data, "inline_data"},
+       {Opt_flush_merge, "flush_merge"},
        {Opt_err, NULL},
 };
 
@@ -334,6 +336,9 @@ static int parse_options(struct super_block *sb, char *options)
                case Opt_inline_data:
                        set_opt(sbi, INLINE_DATA);
                        break;
+               case Opt_flush_merge:
+                       set_opt(sbi, FLUSH_MERGE);
+                       break;
                default:
                        f2fs_msg(sb, KERN_ERR,
                                "Unrecognized mount option \"%s\" or missing value",
@@ -537,6 +542,8 @@ static int f2fs_show_options(struct seq_file *seq, struct dentry *root)
                seq_puts(seq, ",disable_ext_identify");
        if (test_opt(sbi, INLINE_DATA))
                seq_puts(seq, ",inline_data");
+       if (test_opt(sbi, FLUSH_MERGE))
+               seq_puts(seq, ",flush_merge");
        seq_printf(seq, ",active_logs=%u", sbi->active_logs);
 
        return 0;