Re: [PATCH v4 3/3] mm/page_alloc: Optimize __free_contig_frozen_range()

David Hildenbrand (Arm)
2026-03-30T14:40:15Z

On 3/27/26 13:57, Muhammad Usama Anjum wrote:
> Apply the same batch-freeing optimization from free_contig_range() to the
> frozen page path. The previous __free_contig_frozen_range() freed each
> order-0 page individually via free_frozen_pages(), which is slow for the
> same reason the old free_contig_range() was: each page goes to the
> order-0 pcp list rather than being coalesced into higher-order blocks.
>
> Rewrite __free_contig_frozen_range() to call free_pages_prepare() for
> each order-0 page, then batch the prepared pages into the largest
> possible power-of-2 aligned chunks via free_prepared_contig_range().
> If free_pages_prepare() fails (e.g. HWPoison, bad page) the page is
> deliberately not freed; it should not be returned to the allocator.
>
> I've tested CMA through debugfs. The test allocates 16384 pages per
> allocation for several iterations. There is 3.5x improvement.
>
> Before: 1406 usec per iteration
> After: 402 usec per iteration
>
> Before:
>
> 70.89% 0.69% cma [kernel.kallsyms] [.] free_contig_frozen_range
> |
> |--70.20%--free_contig_frozen_range
> | |
> | |--46.41%--__free_frozen_pages
> | | |
> | | --36.18%--free_frozen_page_commit
> | | |
> | | --29.63%--_raw_spin_unlock_irqrestore
> | |
> | |--8.76%--_raw_spin_trylock
> | |
> | |--7.03%--__preempt_count_dec_and_test
> | |
> | |--4.57%--_raw_spin_unlock
> | |
> | |--1.96%--__get_pfnblock_flags_mask.isra.0
> | |
> | --1.15%--free_frozen_page_commit
> |
> --0.69%--el0t_64_sync
>
> After:
>
> 23.57% 0.00% cma [kernel.kallsyms] [.] free_contig_frozen_range
> |
> ---free_contig_frozen_range
> |
> |--20.45%--__free_contig_frozen_range
> | |
> | |--17.77%--free_pages_prepare
> | |
> | --0.72%--free_prepared_contig_range
> | |
> | --0.55%--__free_frozen_pages
> |
> --3.12%--free_pages_prepare
>
> Suggested-by: Zi Yan <ziy@nvidia.com>
> Signed-off-by: Muhammad Usama Anjum <usama.anjum@arm.com>
> ---

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

--
Cheers,

David