| Message ID | 20210902164412.9994-1-shaoyi@amazon.com |
|---|---|
| Headers | show |
| Series | ext4: fix lazy initialization next schedule time computation in more granular unit | expand |
Here are more context and testing details: This issue was originally identified in Amazon Linux 2 with kernel 5.10 and CONFIG_HZ is 250 in x86_64 while 100 in arm64. It can be reproduced by launching EC2 instances c5.2xlarge (x86_64) and c6g.2xlarge (arm64) then measuring time to finish ext4lazyinit thread after mounting the ext4 FS. w/o fix in kernel 5.10 |----------------+-------------+------------| | ext4 FS volume | c6g.2xlarge | c5.2xlarge | |----------------+-------------+------------| | 2T | 1842 secs | 743 secs | |----------------+-------------+------------| | 3T | 2690 secs | 1110 secs | |----------------+-------------+------------| w/ fix in kernel 5.10 |----------------+-------------+------------| | ext4 FS volume | c6g.2xlarge | c5.2xlarge | |----------------+-------------+------------| | 2T | 660 secs | 544 secs | |----------------+-------------+------------| | 3T | 1053 secs | 932 secs | |----------------+-------------+------------| On Thu, Sep 02, 2021 at 04:44:11PM +0000, Shaoying Xu wrote: > Description > =========== > Ext4 FS has inappropriate implementations on the next schedule time calculation > that use jiffies to measure the time for one request to zero out inode table. This > actually makes the wait time effectively dependent on CONFIG_HZ, which is > undesirable. We have observed on server systems with 100HZ some fairly long delays > in initialization as a result. Therefore, we propose to use more granular unit to > calculate the next schedule time. > > Test > ==== > Tested the patch in stable kernel 5.10 with FS volume 2T and 3T on EC2 > instances. Before the fix, instances with 250HZ finished the lazy initialization > in around 2.4x time less than instances with 100HZ. > After the fix, both of them finished within approximately same time. > > Patch > ===== > Shaoying Xu (1): > ext4: fix lazy initialization next schedule time computation in more > granular unit > > fs/ext4/super.c | 9 ++++----- > 1 file changed, 4 insertions(+), 5 deletions(-) > > -- > 2.16.6 >
On Thu, 2 Sep 2021 16:44:11 +0000, Shaoying Xu wrote: > Description > =========== > Ext4 FS has inappropriate implementations on the next schedule time calculation > that use jiffies to measure the time for one request to zero out inode table. This > actually makes the wait time effectively dependent on CONFIG_HZ, which is > undesirable. We have observed on server systems with 100HZ some fairly long delays > in initialization as a result. Therefore, we propose to use more granular unit to > calculate the next schedule time. > > [...] Applied, thanks! [1/1] ext4: fix lazy initialization next schedule time computation in more granular unit commit: 3782027982881d2c1105ffe058aecb69cc780dfa Best regards,
Description =========== Ext4 FS has inappropriate implementations on the next schedule time calculation that use jiffies to measure the time for one request to zero out inode table. This actually makes the wait time effectively dependent on CONFIG_HZ, which is undesirable. We have observed on server systems with 100HZ some fairly long delays in initialization as a result. Therefore, we propose to use more granular unit to calculate the next schedule time. Test ==== Tested the patch in stable kernel 5.10 with FS volume 2T and 3T on EC2 instances. Before the fix, instances with 250HZ finished the lazy initialization in around 2.4x time less than instances with 100HZ. After the fix, both of them finished within approximately same time. Patch ===== Shaoying Xu (1): ext4: fix lazy initialization next schedule time computation in more granular unit fs/ext4/super.c | 9 ++++----- 1 file changed, 4 insertions(+), 5 deletions(-)