Re: [PATCH RFC v3 12/35] mm: Call arch_swap_prepare_to_restore() before arch_swap_restore()

Anshuman Khandual
2024-02-01T03:30:55Z

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 ?