linux-kernel - Re: [PATCH v2 1/4] mm/page_alloc/vmstat: Simplify refresh_cpu_vm

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Message-ID: <202509260132.awvdNKqF-lkp@intel.com>
Date: Fri, 26 Sep 2025 18:34:06 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: oe-kbuild@...ts.linux.dev, Joshua Hahn <joshua.hahnjy@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Johannes Weiner <hannes@...xchg.org>
Cc: lkp@...el.com, oe-kbuild-all@...ts.linux.dev,
	Linux Memory Management List <linux-mm@...ck.org>,
	Chris Mason <chris.mason@...ionio.com>,
	Kiryl Shutsemau <kirill@...temov.name>,
	"Liam R. Howlett" <Liam.Howlett@...cle.com>,
	Brendan Jackman <jackmanb@...gle.com>,
	David Hildenbrand <david@...hat.com>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	Michal Hocko <mhocko@...e.com>, Mike Rapoport <rppt@...nel.org>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Vlastimil Babka <vbabka@...e.cz>, Zi Yan <ziy@...dia.com>,
	linux-kernel@...r.kernel.org, kernel-team@...a.com
Subject: Re: [PATCH v2 1/4] mm/page_alloc/vmstat: Simplify
 refresh_cpu_vm_stats change detection

Hi Joshua,

kernel test robot noticed the following build warnings:

url:    https://github.com/intel-lab-lkp/linux/commits/Joshua-Hahn/mm-page_alloc-vmstat-Simplify-refresh_cpu_vm_stats-change-detection/20250925-044532
base:   097a6c336d0080725c626fda118ecfec448acd0f
patch link:    https://lore.kernel.org/r/20250924204409.1706524-2-joshua.hahnjy%40gmail.com
patch subject: [PATCH v2 1/4] mm/page_alloc/vmstat: Simplify refresh_cpu_vm_stats change detection
config: mips-randconfig-r073-20250925 (https://download.01.org/0day-ci/archive/20250926/202509260132.awvdNKqF-lkp@intel.com/config)
compiler: clang version 22.0.0git (https://github.com/llvm/llvm-project cafc064fc7a96b3979a023ddae1da2b499d6c954)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@...el.com>
| Reported-by: Dan Carpenter <dan.carpenter@...aro.org>
| Closes: https://lore.kernel.org/r/202509260132.awvdNKqF-lkp@intel.com/

smatch warnings:
mm/page_alloc.c:2591 decay_pcp_high() error: uninitialized symbol 'todo'.

vim +/todo +2591 mm/page_alloc.c

06fb80866d37b0 Joshua Hahn    2025-09-24  2564  bool decay_pcp_high(struct zone *zone, struct per_cpu_pages *pcp)
51a755c56dc05a Ying Huang     2023-10-16  2565  {
51a755c56dc05a Ying Huang     2023-10-16  2566  	int high_min, to_drain, batch;
06fb80866d37b0 Joshua Hahn    2025-09-24  2567  	bool todo;

needs to be initialized to false.

51a755c56dc05a Ying Huang     2023-10-16  2568  
51a755c56dc05a Ying Huang     2023-10-16  2569  	high_min = READ_ONCE(pcp->high_min);
51a755c56dc05a Ying Huang     2023-10-16  2570  	batch = READ_ONCE(pcp->batch);
51a755c56dc05a Ying Huang     2023-10-16  2571  	/*
51a755c56dc05a Ying Huang     2023-10-16  2572  	 * Decrease pcp->high periodically to try to free possible
51a755c56dc05a Ying Huang     2023-10-16  2573  	 * idle PCP pages.  And, avoid to free too many pages to
51a755c56dc05a Ying Huang     2023-10-16  2574  	 * control latency.  This caps pcp->high decrement too.
51a755c56dc05a Ying Huang     2023-10-16  2575  	 */
51a755c56dc05a Ying Huang     2023-10-16  2576  	if (pcp->high > high_min) {
51a755c56dc05a Ying Huang     2023-10-16  2577  		pcp->high = max3(pcp->count - (batch << CONFIG_PCP_BATCH_SCALE_MAX),
51a755c56dc05a Ying Huang     2023-10-16  2578  				 pcp->high - (pcp->high >> 3), high_min);
51a755c56dc05a Ying Huang     2023-10-16  2579  		if (pcp->high > high_min)
06fb80866d37b0 Joshua Hahn    2025-09-24  2580  			todo = true;
51a755c56dc05a Ying Huang     2023-10-16  2581  	}
51a755c56dc05a Ying Huang     2023-10-16  2582  
51a755c56dc05a Ying Huang     2023-10-16  2583  	to_drain = pcp->count - pcp->high;
51a755c56dc05a Ying Huang     2023-10-16  2584  	if (to_drain > 0) {
51a755c56dc05a Ying Huang     2023-10-16  2585  		spin_lock(&pcp->lock);
51a755c56dc05a Ying Huang     2023-10-16  2586  		free_pcppages_bulk(zone, to_drain, pcp, 0);
51a755c56dc05a Ying Huang     2023-10-16  2587  		spin_unlock(&pcp->lock);
06fb80866d37b0 Joshua Hahn    2025-09-24  2588  		todo = true;
51a755c56dc05a Ying Huang     2023-10-16  2589  	}
51a755c56dc05a Ying Huang     2023-10-16  2590  
51a755c56dc05a Ying Huang     2023-10-16 @2591  	return todo;
51a755c56dc05a Ying Huang     2023-10-16  2592  }

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki