Re: [PATCH v3] mm: Add CONFIG_PAGE_BLOCK_ORDER to select page block order

[Andrew Morton <akpm@linux-foundation.org>]

On Mon,  5 May 2025 17:22:58 -0700 Juan Yescas <jyescas@google.com> wrote:

> Problem: On large page size configurations (16KiB, 64KiB), the CMA
> alignment requirement (CMA_MIN_ALIGNMENT_BYTES) increases considerably,
> and this causes the CMA reservations to be larger than necessary.
> This means that system will have less available MIGRATE_UNMOVABLE and
> MIGRATE_RECLAIMABLE page blocks since MIGRATE_CMA can't fallback to them.

Thanks, I'll add this for testing while we consider the proposal.

> +# as per include/linux/mmzone.h.
> +config PAGE_BLOCK_ORDER
> +	int "Page Block Order"
> +	range 1 10 if !ARCH_FORCE_MAX_ORDER
> +	default 10 if !ARCH_FORCE_MAX_ORDER
> +	range 1 ARCH_FORCE_MAX_ORDER if ARCH_FORCE_MAX_ORDER
> +	default ARCH_FORCE_MAX_ORDER if ARCH_FORCE_MAX_ORDER
> +
> +	help
> +	  The page block order refers to the power of two number of pages that
> +	  are physically contiguous and can have a migrate type associated to
> +	  them. The maximum size of the page block order is limited by
> +	  ARCH_FORCE_MAX_ORDER.
> +
> +	  This option allows overriding the default setting when the page
> +	  block order requires to be smaller than ARCH_FORCE_MAX_ORDER.
> +
> +	  Reducing pageblock order can negatively impact THP generation
> +	  successful rate. If your workloads uses THP heavily, please use this
> +	  option with caution.
> +
> +	  Don't change if unsure.
> +

I messed with the text a little.

--- a/mm/Kconfig~mm-add-config_page_block_order-to-select-page-block-order-fix
+++ a/mm/Kconfig
@@ -1028,10 +1028,10 @@ config PAGE_BLOCK_ORDER
 	  ARCH_FORCE_MAX_ORDER.
 
 	  This option allows overriding the default setting when the page
-	  block order requires to be smaller than ARCH_FORCE_MAX_ORDER.
+	  block order is required to be smaller than ARCH_FORCE_MAX_ORDER.
 
 	  Reducing pageblock order can negatively impact THP generation
-	  successful rate. If your workloads uses THP heavily, please use this
+	  success rate. If your workloads uses THP heavily, please use this
 	  option with caution.
 
 	  Don't change if unsure.
_