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/fs/f2fs/segment.c b/fs/f2fs/segment.c
index f799c6a..085f548 100644
--- 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 @@
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 @@
{
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 @@
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 @@
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 @@
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);
}