linux-kernel - Re: [PATCH 1/8] mm: move highest_order() and next

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Date: Wed, 8 May 2024 10:13:23 +0800
From: Baolin Wang <baolin.wang@...ux.alibaba.com>
To: Ryan Roberts <ryan.roberts@....com>, akpm@...ux-foundation.org,
 hughd@...gle.com
Cc: willy@...radead.org, david@...hat.com, ioworker0@...il.com,
 wangkefeng.wang@...wei.com, ying.huang@...el.com, 21cnbao@...il.com,
 shy828301@...il.com, ziy@...dia.com, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/8] mm: move highest_order() and next_order() out of the
 THP config



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 */