Re: [PATCH] mm: Fix vmstat after removing NR_BOUNCE

["Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>]

On Thu, May 29, 2025 at 12:40:21PM +0200, Vlastimil Babka wrote:
> On 5/29/25 12:38, Kirill A. Shutemov wrote:
> > Hongyu noticed that the nr_unaccepted counter kept growing even in the
> > absence of unaccepted memory on the machine.
> > 
> > This happens due to a commit that removed NR_BOUNCE: it removed the
> > counter from the enum zone_stat_item, but left it in the vmstat_text
> > array.
> > 
> > As a result, all counters below nr_bounce in /proc/vmstat are
> > shifted by one line, causing the numa_hit counter to be labeled as
> > nr_unaccepted.
> > 
> > To fix this issue, remove nr_bounce from the vmstat_text array.
> > 
> > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> > Reported-by: Hongyu Ning <hongyu.ning@linux.intel.com>
> > Fixes: 194df9f66db8 ("mm: remove NR_BOUNCE zone stat")
> > Cc: stable@vger.kernel.org
> > Cc: Christoph Hellwig <hch@lst.de>
> > Cc: Hannes Reinecke <hare@suse.de>
> > Cc: Johannes Thumshirn <johannes.thumshirn@wdc.com>
> > Cc: Jens Axboe <axboe@kernel.dk>
> 
> Is there a way to add a BUILD_BUG_ON to catch a future case like this one?

There's

	BUILD_BUG_ON(ARRAY_SIZE(vmstat_text) < NR_VMSTAT_ITEMS);

in vmstat_start().

Making it strict != seems to do the trick for my config. But it requires
wider testing.

I can prepare a patch for that.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov