mm/khugepaged: fix comment for default scan sleep duration

mm/khugepaged: fix comment for default scan sleep duration

The comment for khugepaged_scan_sleep_millisecs incorrectly states the
default scan period is 30 seconds.  The actual default value in the code
is 10000ms (10 seconds).

This patch corrects the comment to match the code, preventing potential
confusion.  The incorrect comment has existed since the feature was first
introduced.  While at it, replace the magic value 512 by HPAGE_PMD_NR and
use 'ptes'.

Link: https://lkml.kernel.org/r/20251015092957.37432-1-lianux.mm@gmail.com
Signed-off-by: wang lian <lianux.mm@gmail.com>
Suggested-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Dev Jain <dev.jain@arm.com>
Reviewed-by: Wei Yang <richard.weiyang@gmail.com>
Reviewed-by: Lance Yang <lance.yang@linux.dev>
Acked-by: David Hildenbrand <david@redhat.com>
Reviewed-by: SeongJae Park <sj@kernel.org>
Reviewed-by: Vishal Moola (Oracle) <vishal.moola@gmail.com>
Acked-by: Nico Pache <npache@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>