On Thu, Jan 31, 2019 at 01:37:04PM -0500, Jerome Glisse wrote:
> From: Jérôme Glisse <jglisse@xxxxxxxxxx>
>
> Use unsigned for event field in range struct so that we can also set
> flags with the event. This patch change the field and introduce the
> helper.
>
> Signed-off-by: Jérôme Glisse <jglisse@xxxxxxxxxx>
> Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
> Cc: Peter Xu <peterx@xxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> Cc: Radim Krčmář <rkrcmar@xxxxxxxxxx>
> Cc: kvm@xxxxxxxxxxxxxxx
> ---
> include/linux/mmu_notifier.h | 8 ++++++--
> 1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/mmu_notifier.h b/include/linux/mmu_notifier.h
> index be873c431886..d7a35975c2bd 100644
> --- a/include/linux/mmu_notifier.h
> +++ b/include/linux/mmu_notifier.h
> @@ -6,6 +6,7 @@
> #include <linux/spinlock.h>
> #include <linux/mm_types.h>
> #include <linux/srcu.h>
> +#include <linux/log2.h>
>
> struct mmu_notifier;
> struct mmu_notifier_ops;
> @@ -38,8 +39,11 @@ enum mmu_notifier_event {
> MMU_NOTIFY_PROTECTION_VMA,
> MMU_NOTIFY_PROTECTION_PAGE,
> MMU_NOTIFY_SOFT_DIRTY,
> + MMU_NOTIFY_EVENT_MAX
> };
>
> +#define MMU_NOTIFIER_EVENT_BITS order_base_2(MMU_NOTIFY_EVENT_MAX)
> +
> #ifdef CONFIG_MMU_NOTIFIER
>
> /*
> @@ -60,7 +64,7 @@ struct mmu_notifier_range {
> struct mm_struct *mm;
> unsigned long start;
> unsigned long end;
> - enum mmu_notifier_event event;
> + unsigned event;
> bool blockable;
> };
This is only allocated in the stack, so saving RAM by mixing bitfields
with enum in the same 4 bytes to save 4 bytes isn't of maximum
priority.
A possibly cleaner way to save those 4 bytes without mixing enum with
bitfields by hand, is to add a "unsigned short flags" which will make
"event/flags/blockable" fit in the same 8 bytes (bool only needs 1
byte) as before the patch (the first bitfield can start from 0 then).
Yet another way is to drop blockable and convert it to a flag in
"unsigned int flags".
