RE: [PATCH 4/5] [RFC][HACK] Add LRU_VOLATILE support to the VM

[Dan Magenheimer]

> From: Minchan Kim [mailto:minchan@xxxxxxxxxx]
> To: John Stultz
> Subject: Re: [PATCH 4/5] [RFC][HACK] Add LRU_VOLATILE support to the VM

Hi Minchan --

Thanks for cc'ing me on this!

> Targets for the LRU list could be following as in future
> 
> 1. volatile pages in this patchset.
> 2. ephemeral pages of tmem
> 3. madivse(DONTNEED)
> 4. fadvise(NOREUSE)
> 5. PG_reclaimed pages
> 6. clean pages if we write CFLRU(clean first LRU)
> 
> So if any guys have objection, please raise your hands
> before further progress.

I agree that the existing shrinker mechanism is too primitive
and the kernel needs to take into account more factors in
deciding how to quickly reclaim pages from a broader set
of sources.  However, I think it is important to ensure
that both the "demand" side and the "supply" side are
studied.  There has to be some kind of prioritization policy
among all the RAM consumers so that a lower-priority
alloc_page doesn't cause a higher-priority "volatile" page
to be consumed.  I suspect this policy will be VERY hard to
define and maintain.

Related, ephemeral pages in tmem are not truly volatile
as there is always at least one tmem data structure pointing
to it.  I haven't followed this thread previously so my apologies
if it already has this, but the LRU_VOLATILE list might
need to support a per-page "garbage collection" callback.

Dan
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