Re: Re: Re: Re: [PATCH v18 01/14] mm/page_ext: Export lookup_page_ext() to GPL modules

On Mon, 13 Jul 2020 19:38:05 +0200 SeongJae Park [off-list ref] wrote:

On Mon, 13 Jul 2020 20:19:09 +0300 Mike Rapoport [off-list ref] wrote:

quoted

On Mon, Jul 13, 2020 at 02:21:43PM +0200, SeongJae Park wrote:

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On Mon, 13 Jul 2020 15:08:42 +0300 Mike Rapoport [off-list ref] wrote:

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Hi,

On Mon, Jul 13, 2020 at 10:41:31AM +0200, SeongJae Park wrote:

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From: SeongJae Park <redacted>

This commit exports 'lookup_page_ext()' to GPL modules.  It will be used
by DAMON in following commit for the implementation of the region based
sampling.

Maybe I'm missing something, but why is DAMON a module?

I made it loadable just for easier adoption from downstream kernels.  I could
drop the module build support if asked.

 
Well, exporting core mm symbols to modules should be considred very
carefully. 

Agreed.  I will drop the module support from the next spin.

quoted

Why lookup_page_ext() is required for DAMON? It is not used anywhere in
this patchset.

It's indirectly used.  In the 6th patch, DAMON uses 'set_page_young()' to not
interfere with other PTE Accessed bit users.  And, 'set_page_young()' uses
'lookup_page_ext()' if !CONFIG_64BIT.  That's why I exported it.

This also means that it would make no sense if !64BIT && !PAGE_EXTENSION.  In
the next spin, I will update the DAMON Kconfig to select PAGE_EXTENSION if
!64BIT, as same to that of IDLE_PAGE_TRACKING.


Thanks,
SeongJae Park