On Wed, Mar 17, 2021 at 08:30:56PM +0530, Shashidhar Patil wrote: > Hi Theodore, > Thank you for the details about the journalling layer and > insight into the block device layer. > I think Good luck might have clicked. The swap file in our case is > attached to a loop block device before enabling swap using swapon. > Since loop driver processes its IO requests by calling > vfs_iter_write() the write requests re-enter the ext4 > filesystem/journalling code. > Is that right ? There seems to be a possibility of cylic dependency. If that hypothesis is correct, you should see an example of that in one of your stack traces; do you? The loop device creates struct file where the file is opened using O_DIRECT. In the O_DIRECT code path, assuming the file was fully allocate and initialized, it shouldn't involve starting a journal handle. That being said, why are you using a loop device for a swap device at all? Using a swap file directly is going to be much more efficient, and decrease the stack depth and CPU cycles needed to do a swap out if nothing else. If you can reliably reproduce the problem, what happens if you use a swap file directly and cut out the loop device as a swap device? Does it make the problem go away? - Ted
