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

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Message-ID: <20191018074411.GC5017@dhcp22.suse.cz>
Date:   Fri, 18 Oct 2019 09:44:11 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     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 Wed 16-10-19 15:11:48, Dave Hansen wrote:
> We're starting to see systems with more and more kinds of memory such
> as Intel's implementation of persistent memory.
> 
> Let's say you have a system with some DRAM and some persistent memory.
> Today, once DRAM fills up, reclaim will start and some of the DRAM
> contents will be thrown out.  Allocations will, at some point, start
> falling over to the slower persistent memory.
> 
> That has two nasty properties.  First, the newer allocations can end
> up in the slower persistent memory.  Second, reclaimed data in DRAM
> are just discarded even if there are gobs of space in persistent
> memory that could be used.
> 
> This set implements a solution to these problems.  At the end of the
> reclaim process in shrink_page_list() just before the last page
> refcount is dropped, the page is migrated to persistent memory instead
> of being dropped.
> 
> While I've talked about a DRAM/PMEM pairing, this approach would
> function in any environment where memory tiers exist.
> 
> This is not perfect.  It "strands" pages in slower memory and never
> brings them back to fast DRAM.  Other things need to be built to
> promote hot pages back to DRAM.
> 
> This is part of a larger patch set.  If you want to apply these or
> play with them, I'd suggest using the tree from here.  It includes
> autonuma-based hot page promotion back to DRAM:
> 
> 	http://lkml.kernel.org/r/c3d6de4d-f7c3-b505-2e64-8ee5f70b2118@intel.com
> 
> This is also all based on an upstream mechanism that allows
> persistent memory to be onlined and used as if it were volatile:
> 
> 	http://lkml.kernel.org/r/20190124231441.37A4A305@viggo.jf.intel.com

How does this compare to
http://lkml.kernel.org/r/1560468577-101178-1-git-send-email-yang.shi@linux.alibaba.com?

-- 
Michal Hocko
SUSE Labs