Peter Xu <peterx@xxxxxxxxxx> writes:
> When page migration happens, we always ignore the young/dirty bit settings
> in the old pgtable, and marking the page as old in the new page table using
> either pte_mkold() or pmd_mkold(), and keeping the pte clean.
>
> That's fine from functional-wise, but that's not friendly to page reclaim
> because the moving page can be actively accessed within the procedure. Not
> to mention hardware setting the young bit can bring quite some overhead on
> some systems, e.g. x86_64 needs a few hundreds nanoseconds to set the bit.
> The same slowdown problem to dirty bits when the memory is first written
> after page migration happened.
>
> Actually we can easily remember the A/D bit configuration and recover the
> information after the page is migrated. To achieve it, define a new set of
> bits in the migration swap offset field to cache the A/D bits for old pte.
> Then when removing/recovering the migration entry, we can recover the A/D
> bits even if the page changed.
>
> One thing to mention is that here we used max_swapfile_size() to detect how
> many swp offset bits we have, and we'll only enable this feature if we know
> the swp offset can be big enough to store both the PFN value and the young
~~~~~
Nitpick: A/D
> bit. Otherwise the A/D bits are dropped like before.
>
> Signed-off-by: Peter Xu <peterx@xxxxxxxxxx>
> ---
> include/linux/swapops.h | 99 +++++++++++++++++++++++++++++++++++++++++
> mm/huge_memory.c | 18 +++++++-
> mm/migrate.c | 6 ++-
> mm/migrate_device.c | 4 ++
> mm/rmap.c | 5 ++-
> 5 files changed, 128 insertions(+), 4 deletions(-)
>
> diff --git a/include/linux/swapops.h b/include/linux/swapops.h
> index e1accbcd1136..0e9579b90659 100644
> --- a/include/linux/swapops.h
> +++ b/include/linux/swapops.h
> @@ -8,6 +8,10 @@
>
> #ifdef CONFIG_MMU
>
> +#ifdef CONFIG_SWAP
> +#include <linux/swapfile.h>
> +#endif /* CONFIG_SWAP */
I don't think we need the comment here. The #ifdef is too near. But
this isn't a big deal.
Best Regards,
Huang, Ying
