On Fri, 30 Aug 2024 at 14:08, Dave Airlie <airlied@xxxxxxxxx> wrote:
>
> The TTM revert is due to some stuttering graphical apps probably due
> to longer stalls while prefaulting.
Yeah, trying to pre-fault a PMD worth of pages in one go is just crazy talk.
Now, if it was PMD-aligned and you faulted in a single PMD, that would
be different. But just doing prn_insert_page() in a loop is insane.
The code doesn't even stop when it hits a page that already existed,
and it keeps locking and unlocking the last-level page table over and
over again.
Honestly, that code is questionable even for the *small* value, much
less the "a PMD size" case.
Now, if you have an array of 'struct page *", you can use
vm_insert_pages(), and that's reasonably efficient.
And if you have a *contiguous* are of pfns, you can use remap_pfn_range().
But that "insert one pfn at a time" that the drm layer does is
complete garbage. You're not speeding anything up, you're just digging
deeper.
Linus
