Re: [PATCH v2 2/3] mm, page_owner: decouple freeing stack trace from debug_pagealloc

Kirill A. Shutemov
2019-10-01T12:31:55Z

On Tue, Oct 01, 2019 at 08:26:28AM -0400, Qian Cai wrote:
> On Tue, 2019-10-01 at 14:51 +0300, Kirill A. Shutemov wrote:
> > On Tue, Oct 01, 2019 at 10:07:44AM +0200, Vlastimil Babka wrote:
> > > On 10/1/19 1:49 AM, Qian Cai wrote:
> > > >
> > > >
> > > > > On Sep 30, 2019, at 5:43 PM, Vlastimil Babka <vbabka@suse.cz> wrote:
> > > > >
> > > > > Well, my use case is shipping production kernels with CONFIG_PAGE_OWNER
> > > > > and CONFIG_DEBUG_PAGEALLOC enabled, and instructing users to boot-time
> > > > > enable only for troubleshooting a crash or memory leak, without a need
> > > > > to install a debug kernel. Things like static keys and page_ext
> > > > > allocations makes this possible without CPU and memory overhead when not
> > > > > boot-time enabled. I don't know too much about KASAN internals, but I
> > > > > assume it's not possible to use it that way on production kernels yet?
> > > >
> > > > In that case, why can’t users just simply enable page_owner=on and
> > > > debug_pagealloc=on for troubleshooting? The later makes the kernel
> > > > slower, but I am not sure if it is worth optimization by adding a new
> > > > parameter. There have already been quite a few MM-related kernel
> > > > parameters that could tidy up a bit in the future.
> > >
> > > They can do that and it was intention, yes. The extra parameter was
> > > requested by Kirill, so I'll defer the answer to him :)
> >
> > DEBUG_PAGEALLOC is much more intrusive debug option. Not all architectures
> > support it in an efficient way. Some require hibernation.
> >
> > I don't see a reason to tie these two option together.
>
> Make sense. How about page_owner=on will have page_owner_free=on by default?
> That way we don't need the extra parameter.

It's 0.1% of system memory. Does it matter for a debug option? I don't know.

--
Kirill A. Shutemov