mm/Kconfig: correct description of DEFERRED_STRUCT_PAGE_INIT

mm/Kconfig: correct description of DEFERRED_STRUCT_PAGE_INIT

The description mentions kswapd threads, while the deferred struct page
initialization is actually done by one-off "pgdatinitX" threads.

Fix the description so that potentially users are not confused about
pgdatinit threads using CPU after boot instead of kswapd.

Signed-off-by: Vlastimil Babka <[email protected]>
Acked-by: Mel Gorman <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>