On Wed, Mar 20, 2024 at 11:52:58AM -0500, Frederick Lawler wrote: > Hi Theodore and Ojaswin, > > On Mon, Jan 08, 2024 at 09:53:18PM -0500, Theodore Ts'o wrote: > > > > On Fri, 15 Dec 2023 16:49:49 +0530, Ojaswin Mujoo wrote: > > > This patch intends to fix the recent bugzilla [1] report where the > > > kworker flush thread seemed to be taking 100% CPU utilizationa and was > > > slowing down the whole system. The backtrace indicated that we were > > > stuck in mballoc allocation path. The issue was only seen kernel 6.5+ > > > and when ext4 was mounted with -o stripe (or stripe option was > > > implicitly added due us mkfs flags used). > > > > > > [...] > > > > Applied, thanks! > > I backported this patch to at least 6.6 and tested on our fleet of > software RAID 0 NVME SSD nodes. This change worked very nicely > for us. We're interested in backporting this to at least 6.6. > > I tried looking at xfstests, and didn't really see a good match > (user error?) to validate the fix via that. So I'm a little unclear what > the path forward here is. > > Although we experienced this issue in 6.1, I didn't backport to 6.1 and > test to verify this also works there, however, setting stripe to 0 did in > the 6.1 case. > > Best, > Fred Hi Fred, If I understand correctly, you are looking for a test case which you could use to confirm if the issue exists and if the backport is solving it, right? Actually, I was never able to replicate this at my end so I had to rely on people hitting the bug to confirm if it works. I did set out to write a testcase that could help us reliably replicate this issue but it needs a very specially crafted FS that is a bit difficult to achieve from user space. I was using debugfs to create an FS that could hit it but I kept running into issues where it won't mount etc. Maybe there's a better way to craft such an FS that I'm not aware of. One more option is that maybe we can have KUnit test for this in the mballoc code but I'd need to read some more about the kunit infrastructure to see if it's possible/feasible. Regards, ojaswin > > > > > [1/1] ext4: fallback to complex scan if aligned scan doesn't work > > commit: a26b6faf7f1c9c1ba6edb3fea9d1390201f2ed50 > > > > Best regards, > > -- > > Theodore Ts'o <tytso@xxxxxxx>
