linux-ext4 - [PATCH 1/1] ext4: fix lazy initialization next schedule time computation in more granular unit

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Message-ID: <20210902164412.9994-2-shaoyi@amazon.com>
Date:   Thu, 2 Sep 2021 16:44:12 +0000
From:   Shaoying Xu <shaoyi@...zon.com>
To:     <tytso@....edu>, <adilger.kernel@...ger.ca>
CC:     <linux-ext4@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <benh@...zon.com>, <shaoyi@...zon.com>
Subject: [PATCH 1/1] ext4: fix lazy initialization next schedule time computation in more granular unit

Ext4 file system has default lazy inode table initialization setup once
it is mounted. However, it has issue on computing the next schedule time
that makes the timeout same amount in jiffies but different real time in
secs if with various HZ values. Therefore, fix by measuring the current
time in a more granular unit nanoseconds and make the next schedule time
independent of the HZ value.

Fixes: bfff68738f1c ("ext4: add support for lazy inode table initialization")
Signed-off-by: Shaoying Xu <shaoyi@...zon.com>
Cc: stable@...r.kernel.org
---
 fs/ext4/super.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index dfa09a277b56..399cbe9c14a8 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -3421,9 +3421,9 @@ static int ext4_run_li_request(struct ext4_li_request *elr)
 	struct super_block *sb = elr->lr_super;
 	ext4_group_t ngroups = EXT4_SB(sb)->s_groups_count;
 	ext4_group_t group = elr->lr_next_group;
-	unsigned long timeout = 0;
 	unsigned int prefetch_ios = 0;
 	int ret = 0;
+	u64 start_time;
 
 	if (elr->lr_mode == EXT4_LI_MODE_PREFETCH_BBITMAP) {
 		elr->lr_next_group = ext4_mb_prefetch(sb, group,
@@ -3460,14 +3460,13 @@ static int ext4_run_li_request(struct ext4_li_request *elr)
 		ret = 1;
 
 	if (!ret) {
-		timeout = jiffies;
+		start_time = ktime_get_real_ns();
 		ret = ext4_init_inode_table(sb, group,
 					    elr->lr_timeout ? 0 : 1);
 		trace_ext4_lazy_itable_init(sb, group);
 		if (elr->lr_timeout == 0) {
-			timeout = (jiffies - timeout) *
-				EXT4_SB(elr->lr_super)->s_li_wait_mult;
-			elr->lr_timeout = timeout;
+			elr->lr_timeout = nsecs_to_jiffies((ktime_get_real_ns() - start_time) *
+				EXT4_SB(elr->lr_super)->s_li_wait_mult);
 		}
 		elr->lr_next_sched = jiffies + elr->lr_timeout;
 		elr->lr_next_group = group + 1;
-- 
2.16.6