Re: [PATCH v3] mm/page_owner: fix for deferred struct page init

Michal Hocko
2019-01-04T13:09:09Z

On Thu 03-01-19 17:22:29, Qian Cai wrote:
> On 1/3/19 3:22 PM, Michal Hocko wrote:
> > On Thu 03-01-19 14:53:47, Qian Cai wrote:
> >> On 1/3/19 2:07 PM, Michal Hocko wrote> So can we make the revert with an
> >> explanation that the patch was wrong?
> >>> If we want to make hacks to catch more objects to be tracked then it
> >>> would be great to have some numbers in hands.
> >>
> >> Well, those numbers are subject to change depends on future start_kernel()
> >> order. Right now, there are many functions could be caught earlier by page owner.
> >>
> >> kmemleak_init();
> > [...]
> >> sched_init_smp();
> >
> > The kernel source dump will not tell us much of course. A ball park
> > number whether we are talking about dozen, hundreds or thousands of
> > allocations would tell us something at least, doesn't it.
> >
> > Handwaving that it might help us some is not particurarly useful. We are
> > already losing some allocations already. Does it matter? Well, that
> > depends, sometimes we do want to catch an owner of particular page and
> > it is sad to find nothing. But how many times have you or somebody else
> > encountered that in practice. That is exactly a useful information to
> > judge an ugly ifdefery in the code. See my point?
>
> 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_?

--
Michal Hocko
SUSE Labs