linux-kernel - Re: [PATCH] arm64/hugetlb: fix CMA gigantic page order for non-4K PAGE

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Message-ID: <3747d914-c687-b983-c624-e3418b4d2448@oracle.com>
Date:   Tue, 5 Oct 2021 14:28:03 -0700
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Anshuman Khandual <anshuman.khandual@....com>,
        Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Barry Song <song.bao.hua@...ilicon.com>, stable@...r.kernel.org
Subject: Re: [PATCH] arm64/hugetlb: fix CMA gigantic page order for non-4K
 PAGE_SIZE

On 10/5/21 1:54 PM, Andrew Morton wrote:
> On Tue,  5 Oct 2021 13:25:29 -0700 Mike Kravetz <mike.kravetz@...cle.com> wrote:
> 
>> For non-4K PAGE_SIZE configs, the largest gigantic huge page size is
>> CONT_PMD_SHIFT order.
> 
> What are the user visible effects of this bug?
> 
> 

Sorry,
I only recently got easy access to arm64 platforms.  This is what I saw
as a user:

The largest gigantic huge page size on arm64 with 64K PAGE_SIZE 64K is
16G.  Therefore, one should be able to specify 'hugetlb_cma=16G' on the
kernel command line so that 1 gigantic page can be allocated from CMA.
However, when adding such an option the following message is produced:

hugetlb_cma: cma area should be at least 8796093022208 MiB

This is because the calculation for non-4K gigantic page order is
incorrect in the arm64 specific routine arm64_hugetlb_cma_reserve().

Would you like me to send a new version with this in the commit message?
Or, is it easier for you to just add it?
-- 
Mike Kravetz