On Mon, Aug 06, 2012 at 08:46:18AM -0700, Dan Magenheimer wrote:

quoted

From: Minchan Kim [mailto:minchan@kernel.org]
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!

quoted

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.

Yes. It's another story.
At the moment, VM doesn't consider such priority-inversion problem
excpet giving the more memory to privileged processes. It's so simple
but works well till now.

Related, ephemeral pages in tmem are not truly volatile

"volatile" term is used by John for only his special patch so
I like Ereclaim(Easy Reclaim) rather than 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.

Right. That's why this patch provides purgepage in address_space_operations.
I think zcache could attach own address_space_operations to the page
which is allocated by zbud for instance, zcache_purgepage which is called by VM
when the page is reclaimed. So zcache don't need custom LRU policy(but still need
linked list for managing zbuddy) and pass the decision to the VM.

Dan

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-- 
Kind regards,
Minchan Kim

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