linux-kernel - Re: [PATCH] mm/vmstat: Fix a W=1 clang compiler warning

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Message-ID: <6a45a521-71a3-4087-9320-b8aeecea205a@acm.org>
Date: Tue, 28 Jan 2025 13:36:39 -0800
From: Bart Van Assche <bvanassche@....org>
To: Ivan Shapovalov <intelfx@...elfx.name>,
 Andrew Morton <akpm@...ux-foundation.org>
Cc: Nathan Chancellor <nathan@...nel.org>,
 Nick Desaulniers <ndesaulniers@...gle.com>, Bill Wendling
 <morbo@...gle.com>, Justin Stitt <justinstitt@...gle.com>,
 Pasha Tatashin <pasha.tatashin@...een.com>,
 David Rientjes <rientjes@...gle.com>, David Hildenbrand <david@...hat.com>,
 Vlastimil Babka <vbabka@...e.cz>, Joel Granados <joel.granados@...nel.org>,
 Sourav Panda <souravpanda@...gle.com>, Kaiyang Zhao <kaiyang2@...cmu.edu>,
 Johannes Weiner <hannes@...xchg.org>,
 Konstantin Khlebnikov <koct9i@...il.com>, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [PATCH] mm/vmstat: Fix a W=1 clang compiler warning

On 1/21/25 5:57 PM, Ivan Shapovalov wrote:
>> Spose so.  One always suspects that adding a typecast is a sign that we
>> screwed things up somehow.  The relationship between enums lru_list and
>> node_stat_item is foggy, and I'm unsure whether this is the place to
>> make the transition it.  Perhaps lru_list_name() should take an
>> `unsigned int' arg instead.
> 
> All of these *_name() functions do seem to expect arguments in range of
> the corresponding enums, so perhaps keep those args typed as a form of
> self-documenting code, and do this instead?

If nobody objects I will submit this patch for review after the merge
window has closed:

Subject: [PATCH] mm/vmstat: Fix W=1 clang compiler warnings

Commit 30c2de0a267c ("mm/vmstat: fix a W=1 clang compiler warning")
suppresses some but not all compiler warnings that are reported by clang
when building with W=1 about NR_LRU_BASE and NR_ZONE_LRU_BASE. Hence
revert commit 30c2de0a267c and instead make NR_LRU_BASE and
NR_ZONE_LRU_BASE integer constants instead of enumeration constants.

Cc: Ivan Shapovalov <intelfx@...elfx.name>
Signed-off-by: Bart Van Assche <bvanassche@....org>
---
  include/linux/mmzone.h | 22 +++++++++++++++++++---
  include/linux/vmstat.h |  9 +++++++--
  2 files changed, 26 insertions(+), 5 deletions(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 9540b41894da..92ed919ea99d 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -135,10 +135,19 @@ enum numa_stat_item {
  #define NR_VM_NUMA_EVENT_ITEMS 0
  #endif

+/*
+ * NR_ZONE_LRU_BASE and NR_VM_ZONE_STAT_ITEMS are often added to 
enumeration
+ * constants of another type than enum_zone_stat_item. Define these 
constants
+ * as an integer instead of enum node_stat_item to prevent that the 
compiler
+ * warns about enumeration type mismatches when these constants are used.
+ */
+#define NR_ZONE_LRU_BASE	(1 * __NR_ZONE_LRU_BASE)
+#define NR_VM_ZONE_STAT_ITEMS	(1 * __NR_VM_ZONE_STAT_ITEMS)
+
  enum zone_stat_item {
  	/* First 128 byte cacheline (assuming 64 bit words) */
  	NR_FREE_PAGES,
-	NR_ZONE_LRU_BASE, /* Used only for compaction and reclaim retry */
+	__NR_ZONE_LRU_BASE, /* Used only for compaction and reclaim retry */
  	NR_ZONE_INACTIVE_ANON = NR_ZONE_LRU_BASE,
  	NR_ZONE_ACTIVE_ANON,
  	NR_ZONE_INACTIVE_FILE,
@@ -155,10 +164,17 @@ enum zone_stat_item {
  #ifdef CONFIG_UNACCEPTED_MEMORY
  	NR_UNACCEPTED,
  #endif
-	NR_VM_ZONE_STAT_ITEMS };
+	__NR_VM_ZONE_STAT_ITEMS };
+
+/*
+ * enum lru_list constants are often added to NR_LRU_BASE. Define 
NR_LRU_BASE
+ * as an integer instead of enum node_stat_item to prevent that the 
compiler
+ * warns about enumeration type mismatches.
+ */
+#define NR_LRU_BASE (1 * __NR_LRU_BASE)

  enum node_stat_item {
-	NR_LRU_BASE,
+	__NR_LRU_BASE,
  	NR_INACTIVE_ANON = NR_LRU_BASE, /* must match order of LRU_[IN]ACTIVE */
  	NR_ACTIVE_ANON,		/*  "     "     "   "       "         */
  	NR_INACTIVE_FILE,	/*  "     "     "   "       "         */
diff --git a/include/linux/vmstat.h b/include/linux/vmstat.h
index 9f3a04345b86..eb115b9a50f4 100644
--- a/include/linux/vmstat.h
+++ b/include/linux/vmstat.h
@@ -135,8 +135,13 @@ static inline void vm_events_fold_cpu(int cpu)
  #define count_vm_vma_lock_event(x) do {} while (0)
  #endif

+/*
+ * item##_NORMAL has type enum vm_event_item while ZONE_NORMAL and zid have
+ * type enum zone_type. Suppress compiler warnings about mixing different
+ * enumeration types by converting item##_NORMAL into an int with '1 *'.
+ */
  #define __count_zid_vm_events(item, zid, delta) \
-	__count_vm_events(item##_NORMAL - ZONE_NORMAL + zid, delta)
+	__count_vm_events(1 * item##_NORMAL - ZONE_NORMAL + zid, delta)

  /*
   * Zone and node-based page accounting with per cpu differentials.
@@ -515,7 +520,7 @@ static inline const char *node_stat_name(enum 
node_stat_item item)

  static inline const char *lru_list_name(enum lru_list lru)
  {
-	return node_stat_name(NR_LRU_BASE + (enum node_stat_item)lru) + 3; // 
skip "nr_"
+	return node_stat_name(NR_LRU_BASE + lru) + 3; // skip "nr_"
  }

  #if defined(CONFIG_VM_EVENT_COUNTERS) || defined(CONFIG_MEMCG)