Re: [PATCH] f2fs: fix the discard thread sleep timeout under high utilization

[Chao Yu]

Sahitya,

On 2021/3/15 12:56, Sahitya Tummala wrote:

When f2fs is heavily utilized over 80%, the current discard policy
sets the max sleep timeout of discard thread as 50ms
(DEF_MIN_DISCARD_ISSUE_TIME). But this is set even when there are
no pending discard commands to be issued. This results into
unnecessary frequent and periodic wake ups of the discard thread.
This patch adds check for pending  discard commands in addition
to heavy utilization condition to prevent those wake ups.

Could this commit fix your issue?

https://git.kernel.org/pub/scm/linux/kernel/git/jaegeuk/f2fs.git/commit/?h=dev&id=43f8c47ea7d59c7b2270835f1d7c4618a1ea27b6

Thanks,

Signed-off-by: Sahitya Tummala <stumm...@codeaurora.org>
---
  fs/f2fs/segment.c | 5 ++++-
  1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index dced46c..df30220 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -1112,6 +1112,8 @@ static void __init_discard_policy(struct f2fs_sb_info 
*sbi,
                                struct discard_policy *dpolicy,
                                int discard_type, unsigned int granularity)
  {
+       struct discard_cmd_control *dcc = SM_I(sbi)->dcc_info;
+
        /* common policy */
        dpolicy->type = discard_type;
        dpolicy->sync = true;
@@ -1129,7 +1131,8 @@ static void __init_discard_policy(struct f2fs_sb_info 
*sbi,
                dpolicy->io_aware = true;
                dpolicy->sync = false;
                dpolicy->ordered = true;
-               if (utilization(sbi) > DEF_DISCARD_URGENT_UTIL) {
+               if (utilization(sbi) > DEF_DISCARD_URGENT_UTIL &&
+                               atomic_read(&dcc->discard_cmd_cnt)) {
                        dpolicy->granularity = 1;
                        dpolicy->max_interval = DEF_MIN_DISCARD_ISSUE_TIME;
                }