Re: [PATCH v3 7/7] mm: allow page scrubbing routine(s) to be arch controlled

[Julien Grall <julien@xxxxxxx>]

Hi Jan,

On 25/11/2024 14:32, Jan Beulich wrote:
> Especially when dealing with large amounts of memory, memset() may not
> be very efficient; this can be bad enough that even for debug builds a
> custom function is warranted. We additionally want to distinguish "hot"
> and "cold" cases (with, as initial heuristic, "hot" being for any
> allocations a domain does for itself, assuming that in all other cases
> the page wouldn't be accessed [again] soon). The goal is for accesses
> of "cold" pages to not disturb caches (albeit finding a good balance
> between this and the higher latency looks to be difficult).
>
> Keep the default fallback to clear_page_*() in common code; this may
> want to be revisited down the road.
>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> ---
> v3: Re-base.
> v2: New.
> ---
> The choice between hot and cold in scrub_one_page()'s callers is
> certainly up for discussion / improvement.
>
> --- a/xen/arch/arm/include/asm/page.h
> +++ b/xen/arch/arm/include/asm/page.h
> @@ -144,6 +144,12 @@ extern size_t dcache_line_bytes;
>   
>   #define copy_page(dp, sp) memcpy(dp, sp, PAGE_SIZE)
>   
> +#define clear_page_hot  clear_page
> +#define clear_page_cold clear_page
> +
> +#define scrub_page_hot(page) memset(page, SCRUB_BYTE_PATTERN, PAGE_SIZE)
> +#define scrub_page_cold      scrub_page_hot
This block seems to be common between all the arch but x86. Should we 
add an header in asm generic?
The rest looks fine to me.

Cheers,

--
Julien Grall