On Fri, 24 Jan 2020 17:40:51 +0100 Alexander Graf wrote:
>
> On 24.01.20 14:23, Hillf Danton wrote:
> >
> > 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 pages
> >> that were not accessed in the last X minutes".
> >
> > 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.
> >
<snip>
> >
> > --- a/include/uapi/asm-generic/mman-common.h
> > +++ b/include/uapi/asm-generic/mman-common.h
> > @@ -69,6 +69,7 @@
> >
> > #define MADV_COLD 20 /* deactivate these pages */
> > #define MADV_PAGEOUT 21 /* reclaim these pages */
> > +#define MADV_CCPC 22 /* reclaim cold & clean page cache pages */
>
> This patch adds a new madvise flag. I have a hard time seeing how that
> would help with the "full system expiry" of pages?
>
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 like
> to have a coldness cutoff date at which you can be pretty confident that
> page cache data is no longer needed.
>
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
> 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 */
