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From: Hillf Danton <hdanton@sina.com>
To: Alexander Graf <graf@amazon.com>
Cc: Hillf Danton <hdanton@sina.com>,
	Alexander Duyck <alexander.duyck@gmail.com>,
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	Minchan Kim <minchan@kernel.org>,
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Subject: Re: [PATCH v16.1 0/9] mm / virtio: Provide support for free page reporting
Date: Sat, 25 Jan 2020 10:01:26 +0800
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On Fri, 24 Jan 2020 17:40:51 +0100 Alexander Graf wrote:
>=20
> On 24.01.20 14:23, Hillf Danton wrote:
> >=20
> > On Thu, 23 Jan 2020 11:20:07 +0100 Alexander Graf wrote:
> >>
> >> The big problem I see is that what I really want from a user's point=
 of
> >> view is a tuneable that says "Automatically free clean page cache pa=
ges
> >> that were not accessed in the last X minutes".
> >=20
> > A diff is made on top of 1a4e58cce84e ("mm: introduce MADV_PAGEOUT") =
without
> > test in any form, assuming it goes in line with the tunable above but=
 without
> > "X minutes" taken into account.
> >=20
<snip>
> >=20
> > --- a/include/uapi/asm-generic/mman-common.h
> > +++ b/include/uapi/asm-generic/mman-common.h
> > @@ -69,6 +69,7 @@
> >  =20
> >   #define MADV_COLD	20		/* deactivate these pages */
> >   #define MADV_PAGEOUT	21		/* reclaim these pages */
> > +#define MADV_CCPC	22		/* reclaim cold & clean page cache pages */
>=20
> This patch adds a new madvise flag. I have a hard time seeing how that=20
> would help with the "full system expiry" of pages?
>=20
It works on the basis of individual process now. Shrinking all ccpc
pages in the system without memory pressure...they will be reclaimed
once memory becomes tight.

> The basic point that I tried to make above was that I would ideally lik=
e=20
> to have a coldness cutoff date at which you can be pretty confident tha=
t=20
> page cache data is no longer needed.
>=20
The X minutes need another define like

	#define MADV_DCPC  23   /* deactivate clean page cache pages */

> To work properly, this needs to be transparent to any normal process on=
=20
> the system :).

then task-A on the system can hint kernel like

	madvise(MADV_DCPC);	/* make clean pc pages cold */
	X minutes go by;	/* sieve out hot pages */
	madvise(MADV_CCPC);	/* shrink ccpc */