Re: [RFC 0/7] introduce memory hinting API for external process

[Minchan Kim]

On Mon, May 20, 2019 at 06:44:52PM -0700, Matthew Wilcox wrote:
> On Mon, May 20, 2019 at 12:52:47PM +0900, Minchan Kim wrote:
> > IMHO we should spell it out that this patchset complements MADV_WONTNEED
> > and MADV_FREE by adding non-destructive ways to gain some free memory
> > space. MADV_COLD is similar to MADV_WONTNEED in a way that it hints the
> > kernel that memory region is not currently needed and should be reclaimed
> > immediately; MADV_COOL is similar to MADV_FREE in a way that it hints the
> > kernel that memory region is not currently needed and should be reclaimed
> > when memory pressure rises.
> 
> Do we tear down page tables for these ranges?  That seems like a good

True for MADV_COLD(reclaiming) but false for MADV_COOL(deactivating) at
this implementation.

> way of reclaiming potentially a substantial amount of memory.

Given that consider refauting are spread out over time and reclaim occurs
in burst, that does make sense to speed up the reclaiming. However, a
concern to me is anonymous pages since they need swap cache insertion,
which would be wasteful if they are not reclaimed, finally.