On 1/25/24 22:12, Alexandru Elisei wrote:

arm64 uses arch_swap_restore() to restore saved tags before the page is
swapped in and it's called in atomic context (with the ptl lock held).

Introduce arch_swap_prepare_to_restore() that will allow an architecture to
perform extra work during swap in and outside of a critical section.
This will be used by arm64 to allocate a buffer in memory where to
temporarily save tags if tag storage is not available for the page being
swapped in.

Just wondering if tag storage will always be unavailable for tagged pages
being swapped in ? OR there are cases where allocation might not even be
required ? This prepare phase needs to be outside the critical section -
only because there might be memory allocations ?