linux-kernel - Re: [PATCH 2/2] mm/hugetlb: pass correct order_per_bit to cma_declare_contiguous

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Date: Thu, 4 Apr 2024 11:56:39 -0700
From: Roman Gushchin <roman.gushchin@...ux.dev>
To: Frank van der Linden <fvdl@...gle.com>
Cc: linux-mm@...ck.org, muchun.song@...ux.dev, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] mm/hugetlb: pass correct order_per_bit to
 cma_declare_contiguous_nid

On Thu, Apr 04, 2024 at 04:25:15PM +0000, Frank van der Linden wrote:
> The hugetlb_cma code passes 0 in the order_per_bit argument to
> cma_declare_contiguous_nid (the alignment, computed using the
> page order, is correctly passed in).
> 
> This causes a bit in the cma allocation bitmap to always represent
> a 4k page, making the bitmaps potentially very large, and slower.
> 
> So, correctly pass in the order instead.
> 
> Signed-off-by: Frank van der Linden <fvdl@...gle.com>
> Cc: Roman Gushchin <roman.gushchin@...ux.dev>
> Fixes: cf11e85fc08c ("mm: hugetlb: optionally allocate gigantic hugepages using cma")

Hi Frank,

there is a comment just above your changes which explains why order_per_bit is 0.
Is this not true anymore? If so, please, fix the comment too. Please, clarify.

Thanks!