[f2fs-dev] [PATCH] f2fs: avoid to use slab memory in f2fs_issue_flush for efficiency

[Chao Yu]

If we use slab memory in f2fs_issue_flush(), we will face memory pressure and
latency time caused by racing of kmem_cache_{alloc,free}.

Let's alloc memory in stack instead of slab.

Signed-off-by: Chao Yu <chao2...@samsung.com>
---
 fs/f2fs/segment.c |   28 +++++++++-------------------
 1 file changed, 9 insertions(+), 19 deletions(-)

diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index 2ecbffb..f25f0e0 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -25,7 +25,6 @@
 #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
@@ -238,30 +237,28 @@ repeat:
 int f2fs_issue_flush(struct f2fs_sb_info *sbi)
 {
        struct flush_cmd_control *fcc = SM_I(sbi)->cmd_control_info;
-       struct flush_cmd *cmd;
-       int ret;
+       struct flush_cmd cmd;
 
        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 | __GFP_ZERO);
-       init_completion(&cmd->wait);
+       init_completion(&cmd.wait);
+       cmd.next = NULL;
 
        spin_lock(&fcc->issue_lock);
        if (fcc->issue_list)
-               fcc->issue_tail->next = cmd;
+               fcc->issue_tail->next = &cmd;
        else
-               fcc->issue_list = cmd;
-       fcc->issue_tail = cmd;
+               fcc->issue_list = &cmd;
+       fcc->issue_tail = &cmd;
        spin_unlock(&fcc->issue_lock);
 
        if (!fcc->dispatch_list)
                wake_up(&fcc->flush_wait_queue);
 
-       wait_for_completion(&cmd->wait);
-       ret = cmd->ret;
-       kmem_cache_free(flush_cmd_slab, cmd);
-       return ret;
+       wait_for_completion(&cmd.wait);
+
+       return cmd.ret;
 }
 
 int create_flush_cmd_control(struct f2fs_sb_info *sbi)
@@ -2036,17 +2033,10 @@ 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);
 }
-- 
1.7.10.4



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