Re: [PATCH] mm/vmstat: Fix build with MEMCG=y and VM_EVENT_COUNTERS=n

[Shakeel Butt <shakeel.butt@linux.dev>]

On Wed, Jun 04, 2025 at 12:51:11PM +0300, Kirill A. Shutemov wrote:
> When compiling with MEMCG enabled but VM_EVENT_COUNTERS disabled,
> BUILD_BUG_ON() is triggered in vmstat_start because the vmstat_text
> array is larger than NR_VMSTAT_ITEMS.
> 
> This issue arises because some elements of the vmstat_text array are
> present when either MEMCG or VM_EVENT_COUNTERS is enabled, but
> NR_VMSTAT_ITEMS only accounts for these elements if VM_EVENT_COUNTERS is
> enabled.
> 
> The recent change in the BUILD_BUG_ON() check made it more strict,
> disallowing extra elements in the array, which revealed the issue.
> 
> Instead of adjusting the NR_VMSTAT_ITEMS definition to account for
> MEMCG, make MEMCG select VM_EVENT_COUNTERS. VM_EVENT_COUNTERS is
> enabled in most configurations anyway.
> 
> There is no need to backport this fix to stable trees. Without the
> strict BUILD_BUG_ON(), the issue is not harmful. The elements in
> question would only be read by the memcg code, not by /proc/vmstat.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Reported-by: Randy Dunlap <rdunlap@infradead.org>
> Fixes: ebc5d83d0443 ("mm/memcontrol: use vmstat names for printing statistics")
> Cc: Konstantin Khlebnikov <koct9i@gmail.com>

Acked-by: Shakeel Butt <shakeel.butt@linux.dev>