linux-kernel - [PATCH] f2fs: fix the discard thread sleep timeout under high utilization

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Message-Id: <1615784186-2693-1-git-send-email-stummala@codeaurora.org>
Date:   Mon, 15 Mar 2021 10:26:26 +0530
From:   Sahitya Tummala <stummala@...eaurora.org>
To:     Jaegeuk Kim <jaegeuk@...nel.org>, Chao Yu <yuchao0@...wei.com>,
        linux-f2fs-devel@...ts.sourceforge.net
Cc:     Sahitya Tummala <stummala@...eaurora.org>,
        linux-kernel@...r.kernel.org
Subject: [PATCH] f2fs: fix the discard thread sleep timeout under high utilization

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.

Signed-off-by: Sahitya Tummala <stummala@...eaurora.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;
 		}
-- 
Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project.