linux-kernel - Re: [PATCH] Docs/mm/damon/design: describe the differences for pageout's virtual address and physcial address

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Message-ID: <CAGsJ_4wAx4fA3oR4=JogZ1HAj6fBFRH2c_KmvwSceuPiUWBYFQ@mail.gmail.com>
Date: Sun, 25 Feb 2024 11:33:40 +1300
From: Barry Song <21cnbao@...il.com>
To: SeongJae Park <sj@...nel.org>
Cc: corbet@....net, linux-mm@...ck.org, akpm@...ux-foundation.org, 
	damon@...ts.linux.dev, linux-doc@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Barry Song <v-songbaohua@...o.com>, 
	Minchan Kim <minchan@...nel.org>, Michal Hocko <mhocko@...e.com>, 
	Johannes Weiner <hannes@...xchg.org>
Subject: Re: [PATCH] Docs/mm/damon/design: describe the differences for
 pageout's virtual address and physcial address

On Sun, Feb 25, 2024 at 11:08 AM SeongJae Park <sj@...nel.org> wrote:
>
> Hi Barry,
>
> On Sun, 25 Feb 2024 10:50:23 +1300 Barry Song <21cnbao@...il.com> wrote:
>
> > From: Barry Song <v-songbaohua@...o.com>
> >
> > The doc needs update. As only in the case of virtual address, we are
> > calling madvise() with MADV_PAGEOUT; but in the case of physical
> > address, we are actually calling reclaim_pages() directly. And
> > madvise() with MADV_PAGEOUT is much more aggresive on reclamation
> > compared to reclaim_pages() on paddr.
>
> Thank you for this nice patch :)
>
> >
> > Cc: SeongJae Park <sj@...nel.org>
> > Cc: Minchan Kim <minchan@...nel.org>
> > Cc: Michal Hocko <mhocko@...e.com>
> > Cc: Johannes Weiner <hannes@...xchg.org>
> > Signed-off-by: Barry Song <v-songbaohua@...o.com>
> > ---
> >  Documentation/mm/damon/design.rst | 8 +++++++-
> >  1 file changed, 7 insertions(+), 1 deletion(-)
> >
> > diff --git a/Documentation/mm/damon/design.rst b/Documentation/mm/damon/design.rst
> > index 8c89d26f0baa..6c50743552f5 100644
> > --- a/Documentation/mm/damon/design.rst
> > +++ b/Documentation/mm/damon/design.rst
> > @@ -315,7 +315,13 @@ that supports each action are as below.
> >     Supported by ``vaddr`` and ``fvaddr`` operations set.
> >   - ``cold``: Call ``madvise()`` for the region with ``MADV_COLD``.
> >     Supported by ``vaddr`` and ``fvaddr`` operations set.
> > - - ``pageout``: Call ``madvise()`` for the region with ``MADV_PAGEOUT``.
> > + - ``pageout``: Call ``madvise()`` for the region with ``MADV_PAGEOUT`` if
> > +   the region is using virtual address; otherwise, call ``reclaim_pages()``
> > +   for the region if physical address is used.
> > +   ``madvise()``  with ``MADV_PAGEOUT``  is aggressively reclaiming memory
> > +   when pages are not shared by multiple processes. Differently, paddr's
> > +   pageout  will do the best-effort reclamation by scanning PTEs to figure
> > +   out if pages are young, if not, pages are reclaimed.
>
> I think this might be too much details.  Especially, explanation of
> ``MADV_PAGEOUT`` might better to be done on it's document.  We wouldn't want to
> update two places for future changes to ``MADV_PAGEOUT``.  What do you think
> about making it simple and independent from the implementation detail?  For
> example,
>
>     - - ``pageout``: Call ``madvise()`` for the region with ``MADV_PAGEOUT``.
>     + - ``pageout``: Reclaim the region.

make sense. as someday we might rename reclaim_pages to reclaim_folios or
something else. and we might not use madvise() for vaddr any more, who knows:-)
so it is more sensible to remove the details.
I will send v2 to follow your proposal.

>
> Thanks,
> SJ
>
> >     Supported by ``vaddr``, ``fvaddr`` and ``paddr`` operations set.
> >   - ``hugepage``: Call ``madvise()`` for the region with ``MADV_HUGEPAGE``.
> >     Supported by ``vaddr`` and ``fvaddr`` operations set.
> > --
> > 2.34.1

Thanks
Barry