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Message-ID: <2fcd6dfc-21b7-4e3f-9741-8f0d23d2da5f@linux.alibaba.com>
Date: Wed, 8 May 2024 10:13:23 +0800
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Subject: Re: [PATCH 1/8] mm: move highest_order() and next_order() out of the
 THP config
To: Ryan Roberts <ryan.roberts@arm.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>
 <d9c0ac9df6f6e6176b09fc1ae58146ec4f8d73f5.1714978902.git.baolin.wang@linux.alibaba.com>
 <9576c979-8a11-48e2-aec4-646acf0d8e26@arm.com>
From: Baolin Wang <baolin.wang@linux.alibaba.com>
In-Reply-To: <9576c979-8a11-48e2-aec4-646acf0d8e26@arm.com>
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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).

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 */