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Date: Thu, 4 Apr 2024 13:17:34 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Frank van der Linden <fvdl@google.com>
Cc: linux-mm@kvack.org, muchun.song@linux.dev, linux-kernel@vger.kernel.org,
 Roman Gushchin <roman.gushchin@linux.dev>
Subject: Re: [PATCH 2/2] mm/hugetlb: pass correct order_per_bit to
 cma_declare_contiguous_nid
Message-Id: <20240404131734.5fdd7380202cafcdc44a4d2a@linux-foundation.org>
In-Reply-To: <20240404162515.527802-2-fvdl@google.com>
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	<20240404162515.527802-2-fvdl@google.com>
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On Thu,  4 Apr 2024 16:25:15 +0000 Frank van der Linden <fvdl@google.com> 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.

Ditto.  Should we backport this?   Can we somewhat quantify "potentially very",
and understand under what circumstances this might occur?