linux-kernel - Re: [PATCH] mm/cma: convert cma

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Message-ID: <cf6c758a-42a9-4d4c-a1f7-71f4fc09e8a0@oracle.com>
Date: Tue, 27 Feb 2024 11:26:02 -0800
From: Jianfeng Wang <jianfeng.w.wang@...cle.com>
To: Matthew Wilcox <willy@...radead.org>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        akpm@...ux-foundation.org, sidhartha.kumar@...cle.com
Subject: Re: [PATCH] mm/cma: convert cma_alloc() to return folio



On 2/27/24 11:00 AM, Matthew Wilcox wrote:
> On Tue, Feb 27, 2024 at 10:13:38AM -0800, Jianfeng Wang wrote:
>> Change cma_alloc() to return struct folio. This further increases the
>> usage of folios in mm/hugetlb.
> 
> I love the idea, but I don't think this works.  The memory returned
> from cma_alloc() isn't set up to be a folio, is it?  That is, it
> doesn't have compound_head initialised so that page_folio() on
> consecutive pages will return the same pointer.
> 

Thanks for review.
cma_alloc() returns an array of order-0 pages. So, this commit makes
cma_alloc() return an array of folios (each an order-0 page) rather
than a compound page. Functions that use cma_alloc() do not expect
a compound page as well.

> Or have I misunderstood?