On 2025-11-27 13:54, Mikulas Patocka wrote:
Encrypted swap file is not supposed to work.
Do you have a reference for this? The concept of encrypted swap files
has been a valid workflow for a very long time.
So, this is what happened to you - the machine runs out of memory, it
needs to swap out some pages, dm-crypt encrypts the pages and generates
write bios, the write bios are directed to the loop device, the loop
device directs them to the filesystem, the filesystem attempts to
allocate
more memory => deadlock.
If it's the filesystem trying to allocate memory on writes to a swap
file that is causing a memory allocation/swap race, then any write to a
swap file would engender the same result, regardless of encryption. The
encryption layer is redundant under the failure mode you propose.
I can confirm I have put kernels up to and including 6.14 under heavy
memory stress and have never encountered anything that feels like a
memory allocation race. All my systems have encrypted swap files.
I can't speak toward later kernels, or any bugs that may or may not be
presesnt, but I know of nothing to suggest that encrypted swap files
remain anything other than an intended feature.
Kurt
