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Message-ID: <b5592a14-4add-42a4-89aa-e9a54ed7123c@arm.com>
Date: Wed, 8 May 2024 10:06:18 +0100
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Subject: Re: [PATCH 1/8] mm: move highest_order() and next_order() out of the
 THP config
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To: Baolin Wang <baolin.wang@linux.alibaba.com>, akpm@linux-foundation.org,
 hughd@google.com
Cc: willy@infradead.org, david@redhat.com, ioworker0@gmail.com,
 wangkefeng.wang@huawei.com, ying.huang@intel.com, 21cnbao@gmail.com,
 shy828301@gmail.com, ziy@nvidia.com, linux-mm@kvack.org,
 linux-kernel@vger.kernel.org
References: <cover.1714978902.git.baolin.wang@linux.alibaba.com>
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 <9576c979-8a11-48e2-aec4-646acf0d8e26@arm.com>
 <2fcd6dfc-21b7-4e3f-9741-8f0d23d2da5f@linux.alibaba.com>
From: Ryan Roberts <ryan.roberts@arm.com>
In-Reply-To: <2fcd6dfc-21b7-4e3f-9741-8f0d23d2da5f@linux.alibaba.com>
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On 08/05/2024 03:13, Baolin Wang wrote:
> 
> 
> On 2024/5/7 18:21, Ryan Roberts wrote:
>> On 06/05/2024 09:46, Baolin Wang wrote:
>>> Move highest_order() and next_order() out of the CONFIG_TRANSPARENT_HUGEPAGE
>>> macro, which can be common functions to be used.
>>
>> Sorry if I haven't kept up with the discussion, but why is this needed? I
>> wouldn't expect a need to iterate over orders if THP is compile-time disabled
>> because we will never try to allocate THP?
> 
> Cause I don't want to add some dummy functions to avoid building errors if
> CONFIG_TRANSPARENT_HUGEPAGE is not enabled in patch 6. Another thought is that
> the pagecache can also allocate a large folio even when THP is not enabled, so
> these helpers may be used in the future (not sure though).

OK, I'll admit I haven't looked at the latter patches yet - I'd like to conclude
on the interface and mapping/alignment strategy first.

But it wasn't necessary to access these functions for the anon/private case
without CONFIG_TRANSPARENT_HUGEPAGE, so I'm wondering why it's needed for shmem
case. I would expect that they don't need to be defined at all.

> 
> Anyway, I also have no strong perference for this patch, below dummy functions
> can also work for me:
> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
> index c15bebb2cf53..7aa802ee2ce5 100644
> --- a/include/linux/huge_mm.h
> +++ b/include/linux/huge_mm.h
> @@ -586,6 +586,16 @@ static inline bool thp_migration_supported(void)
>  {
>         return false;
>  }
> +
> +static inline int highest_order(unsigned long orders)
> +{
> +        return 0;
> +}
> +
> +static inline int next_order(unsigned long *orders, int prev)
> +{
> +        return 0;
> +}
>  #endif /* CONFIG_TRANSPARENT_HUGEPAGE */