Re: [PATCH v2 1/1] mm: swap: remove duplicate nr_swap_pages decrement in get_swap_page_of_type()

[Andrew Morton <akpm@linux-foundation.org>]

On Tue, 4 Nov 2025 23:46:40 +0900 YoungJun Park <youngjun.park@lge.com> wrote:

> > Can we please have a description of the userspace-visible runtime
> > effects of the bug?
> > > Fixes: 4f78252da887 ("mm: swap: move nr_swap_pages counter decrement from folio_alloc_swap() to swap_range_alloc()")
> > > Cc: stable@vger.kernel.org # v6.17-rc1
> > 
> > Especially when proposing a backport.
> > 
> > Thanks.
> 
> Hi Andrew,
> 
> Thank you for picking up the patch. Since it's already in mm-hotfixes-unstable,
> I'm providing the elaboration here rather than sending v3.
> 
> As a representative userspace-visible runtime example of the impact,
> /proc/meminfo reports increasingly inaccurate SwapFree values. The
> discrepancy grows with each swap allocation, and during hibernation when
> large amounts of memory are written to swap, the reported value can deviate
> significantly from actual available swap space, misleading users and
> monitoring tools. 

Great, thanks, very helpful.  I pasted that into the mm.git copy of
this patch.