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

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Message-Id: <20211005161542.176a63eb7e197d795c5196d9@linux-foundation.org>
Date:   Tue, 5 Oct 2021 16:15:42 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Mike Kravetz <mike.kravetz@...cle.com>
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 Tue, 5 Oct 2021 14:28:03 -0700 Mike Kravetz <mike.kravetz@...cle.com> wrote:

> 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().

Cool, thanks.

> 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?

I assumed that it would be merged via the same path as the offending
abb7962adc80.  Catalin's arm tree, it appears.