Re: [PATCH v4] mm/page_alloc: replace kernel_init_pages() with batch page clearing

Re: [PATCH v4] mm/page_alloc: replace kernel_init_pages() with batch page clearing

[David Hildenbrand (Arm)]

On 5/4/26 08:39, Hrushikesh Salunke wrote:
> When init_on_alloc is enabled, kernel_init_pages() clears every page
> one at a time via clear_highpage_kasan_tagged(), which incurs per-page
> kmap_local_page()/kunmap_local() overhead and prevents the architecture
> clearing primitive from operating on contiguous ranges.
> 
> Introduce clear_highpages_kasan_tagged() as a static batch clearing
> helper in page_alloc.c that calls clear_pages() for the full contiguous
> range on !HIGHMEM systems, bypassing the per-page kmap overhead and
> allowing a single invocation of the arch clearing primitive across the
> entire allocation. The HIGHMEM path falls back to per-page clearing
> since those pages require kmap.
> 
> Replace kernel_init_pages() with direct calls to the new helper, as it
> becomes a trivial wrapper.
> 
> Allocating 8192 x 2MB HugeTLB pages (16GB) with init_on_alloc=1:
> 
>   Before: 0.445s
>   After:  0.166s  (-62.7%, 2.68x faster)
> 
> Kernel time (sys) reduction per workload with init_on_alloc=1:
> 
>   Workload            Before       After       Change
>   Graph500 64C128T    30m 41.8s    15m 14.8s   -50.3%
>   Graph500 16C32T     15m 56.7s     9m 43.7s   -39.0%
>   Pagerank 32T         1m 58.5s     1m 12.8s   -38.5%
>   Pagerank 128T        2m 36.3s     1m 40.4s   -35.7%
> 
> Signed-off-by: Hrushikesh Salunke <hsalunke@amd.com>
> Acked-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
> Acked-by: Zi Yan <ziy@nvidia.com>
> Acked-by: Pankaj Gupta <pankaj.gupta@amd.com>
> ---

Acked-by: David Hildenbrand (Arm) <david@kernel.org>

-- 
Cheers,

David