Hi folks, I recently traced the code of how dm-thin handles DISCARD requests and found something interesting. In thin_bio_map(), thin device will acquire the virtual and physical bio_prison in sequence when it tries to remap bio based on a private mapping. I know it is necessary to hold these prisons to avoid a possible deadlock when there are parallel discard and non-discard requests to the very same block. However, I am curious about why we need to acquire the virtual bio_prison first instead of trying to acquire only the physical bio_prison. Since all bios from the same thin device (protected by virtual bio_prison) will eventually be passed to physical blocks which are protected by physical bio_prison, it seems that holding only the physical bio_prison is sufficient to prevent discard bios being processed in parallel with any other bios targeting the same block. Any help would be greatly appreciated. Best Regards, Dennis -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
