linux-kernel - Re: [PATCH 0/4] [RFC] Migrate Pages in lieu of discard

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Date:   Fri, 18 Oct 2019 07:54:20 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Michal Hocko <mhocko@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        dan.j.williams@...el.com
Subject: Re: [PATCH 0/4] [RFC] Migrate Pages in lieu of discard

On 10/18/19 12:44 AM, Michal Hocko wrote:
> How does this compare to
> http://lkml.kernel.org/r/1560468577-101178-1-git-send-email-yang.shi@linux.alibaba.com

It's a _bit_ more tied to persistent memory and it appears a bit more
tied to two tiers rather something arbitrarily deep.  They're pretty
similar conceptually although there are quite a few differences.

For instance, what I posted has a static mapping for the migration path.
 If node A is in reclaim, we always try to allocate pages on node B.
There are no restrictions on what those nodes can be.  In Yang Shi's
apporach, there's a dynamic search for a target migration node on each
migration that follows the normal alloc fallback path.  This ends up
making migration nodes special.

There are also some different choices that are pretty arbitrary.  For
instance, when you allocation a migration target page, should you cause
memory pressure on the target?

To be honest, though, I don't see anything fatally flawed with it.  It's
probably a useful exercise to factor out the common bits from the two
sets and see what we can agree on being absolutely necessary.