On 1/4/19 10:17 AM, Michal Hocko wrote: > On Fri 04-01-19 10:01:40, Qian Cai wrote: >> On 1/4/19 8:09 AM, Michal Hocko wrote: >>>> Here is the number without DEFERRED_STRUCT_PAGE_INIT. >>>> >>>> == page_ext_init() after page_alloc_init_late() == >>>> Node 0, zone DMA: page owner found early allocated 0 pages >>>> Node 0, zone DMA32: page owner found early allocated 7009 pages >>>> Node 0, zone Normal: page owner found early allocated 85827 pages >>>> Node 4, zone Normal: page owner found early allocated 75063 pages >>>> >>>> == page_ext_init() before kmemleak_init() == >>>> Node 0, zone DMA: page owner found early allocated 0 pages >>>> Node 0, zone DMA32: page owner found early allocated 6654 pages >>>> Node 0, zone Normal: page owner found early allocated 41907 pages >>>> Node 4, zone Normal: page owner found early allocated 41356 pages >>>> >>>> So, it told us that it will miss tens of thousands of early page allocation call >>>> sites. >>> >>> This is an answer for the first part of the question (how much). The >>> second is _do_we_care_? >> >> Well, the purpose of this simple "ugly" ifdef is to avoid a regression for the >> existing page_owner users with DEFERRED_STRUCT_PAGE_INIT deselected that would >> start to miss tens of thousands early page allocation call sites. > > I am pretty sure we will hear about that when that happens. And act > accordingly. > >> The other option I can think of to not hurt your eyes is to rewrite the whole >> page_ext_init(), init_page_owner(), init_debug_guardpage() to use all early >> functions, so it can work in both with DEFERRED_STRUCT_PAGE_INIT=y and without. >> However, I have a hard-time to convince myself it is a sensible thing to do. > > Or simply make the page_owner initialization only touch the already > initialized memory. Have you explored that option as well? Yes, a proof-of-concept version is v1 where ends up with more ifdefs due to dealing with all the low-level details, https://lore.kernel.org/lkml/20181220060303.38686-1-cai@xxxxxx/
