linux-kernel - Re: [PATCH v1] powerpc/pseries: CMM: Drop page array

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Message-ID: <a2c2f516-c37c-71f5-8f35-c357e8754b17@redhat.com>
Date:   Wed, 25 Sep 2019 09:37:03 +0200
From:   David Hildenbrand <david@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     linux-mm@...ck.org, linuxppc-dev@...ts.ozlabs.org,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Arun KS <arunks@...eaurora.org>,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>
Subject: Re: [PATCH v1] powerpc/pseries: CMM: Drop page array

On 10.09.19 18:39, David Hildenbrand wrote:
> We can simply store the pages in a list (page->lru), no need for a
> separate data structure (+ complicated handling). This is how most
> other balloon drivers store allocated pages without additional tracking
> data.
> 
> For the notifiers, use page_to_pfn() to check if a page is in the
> applicable range. plpar_page_set_loaned()/plpar_page_set_active() were
> called with __pa(page_address()) for now, I assume we can simply switch
> to page_to_phys() here. The pfn_to_kaddr() handling is now mostly gone.
> 
> Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
> Cc: Paul Mackerras <paulus@...ba.org>
> Cc: Michael Ellerman <mpe@...erman.id.au>
> Cc: Arun KS <arunks@...eaurora.org>
> Cc: Pavel Tatashin <pasha.tatashin@...een.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Vlastimil Babka <vbabka@...e.cz>
> Signed-off-by: David Hildenbrand <david@...hat.com>
> ---
> 
> Only compile-tested. I hope the page_to_phys() thingy is correct and I
> didn't mess up something else / ignoring something important why the array
> is needed.
> 
> I stumbled over this while looking at how the memory isolation notifier is
> used - and wondered why the additional array is necessary. Also, I think
> by switching to the generic balloon compaction mechanism, we could get
> rid of the memory hotplug notifier and the memory isolation notifier in
> this code, as the migration capability of the inflated pages is the real
> requirement:
> 	commit 14b8a76b9d53346f2871bf419da2aaf219940c50
> 	Author: Robert Jennings <rcj@...ux.vnet.ibm.com>
> 	Date:   Thu Dec 17 14:44:52 2009 +0000
> 	
> 	    powerpc: Make the CMM memory hotplug aware
> 	
> 	    The Collaborative Memory Manager (CMM) module allocates individual pages
> 	    over time that are not migratable.  On a long running system this can
> 	    severely impact the ability to find enough pages to support a hotplug
> 	    memory remove operation.
> 	[...]
> 
> Thoughts?

Ping, is still feature still used at all?

If nobody can test, any advise on which HW I need and how to trigger it?

-- 

Thanks,

David / dhildenb