Re: [PATCH -mm 0/2] mm: page_ext: split page_ext flags

[Vlastimil Babka <vbabka@suse.cz>]

On 12/17/22 11:58, Yafang Shao wrote:
> On 64bit system, page extension is for debugging purpose only currently,
> because of its overhead, in particular the memory overhead.
> 
> Once a page_ext is enabled, at least it will take 0.2% of the total
> memory because of the page_ext flags, no matter this page_ext uses it or
> not. Currently this page_ext flags is only used for page_owner on 64bit
> system. So it doesn't make sense to allocate this flags for all page_ext
> by default. We'd better move it into page_owner's structure, then when
> someone wants to introduce a new page_ext which may be memory-overhead
> sensitive, it will save this unneeded overhead.
> 
> On 32bit system, there's page_idle running on production envrionment,
> which also uses this page_ext flags. So it will take another 0.2% of
> total memory if the user enable both page_idle and page_owner after this
> change, but considering page_owner is for debugging purpose only, the
> memory overhead in this case won't be a problem.
> 
> So, let split the page_ext flags.

Hi,

FYI I think Pasha's solution should work to avoid the waste even without the
split:

https://lore.kernel.org/all/20230113154253.92480-1-pasha.tatashin@soleen.com/

> Yafang Shao (2):
>   mm: page_owner: split page_owner's flag from the comm flags
>   mm: page_idle: split 32bit page_idle's flag from the common flags
> 
>  include/linux/page_ext.h  | 14 +-------------
>  include/linux/page_idle.h | 39 +++++++++++++++++++++++++++++++++------
>  mm/page_ext.c             | 10 ----------
>  mm/page_idle.c            | 12 ++++++++++++
>  mm/page_owner.c           | 36 ++++++++++++++++++++++--------------
>  5 files changed, 68 insertions(+), 43 deletions(-)
>