linux-kernel - Re: [PATCH v2 1/3] mm/shuffle: don't move pages between zones and don't read garbage memmaps

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Date:   Sat, 20 Jun 2020 01:37:45 +0000
From:   "Williams, Dan J" <dan.j.williams@...el.com>
To:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "david@...hat.com" <david@...hat.com>
CC:     "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "Huang, Ying" <ying.huang@...el.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "richard.weiyang@...il.com" <richard.weiyang@...il.com>,
        "hannes@...xchg.org" <hannes@...xchg.org>,
        "minchan@...nel.org" <minchan@...nel.org>,
        "mhocko@...e.com" <mhocko@...e.com>,
        "mgorman@...hsingularity.net" <mgorman@...hsingularity.net>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH v2 1/3] mm/shuffle: don't move pages between zones and
 don't read garbage memmaps

On Fri, 2020-06-19 at 14:59 +0200, David Hildenbrand wrote:
> Especially with memory hotplug, we can have offline sections (with a
> garbage memmap) and overlapping zones. We have to make sure to only
> touch initialized memmaps (online sections managed by the buddy) and
> that
> the zone matches, to not move pages between zones.
> 
> To test if this can actually happen, I added a simple
> 	BUG_ON(page_zone(page_i) != page_zone(page_j));
> right before the swap. When hotplugging a 256M DIMM to a 4G x86-64 VM
> and
> onlining the first memory block "online_movable" and the second
> memory
> block "online_kernel", it will trigger the BUG, as both zones (NORMAL
> and MOVABLE) overlap.
> 
> This might result in all kinds of weird situations (e.g., double
> allocations, list corruptions, unmovable allocations ending up in the
> movable zone).
> 
> Fixes: e900a918b098 ("mm: shuffle initial free memory to improve
> memory-side-cache utilization")
> Acked-by: Michal Hocko <mhocko@...e.com>
> Cc: stable@...r.kernel.org # v5.2+
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Johannes Weiner <hannes@...xchg.org>
> Cc: Michal Hocko <mhocko@...e.com>
> Cc: Minchan Kim <minchan@...nel.org>
> Cc: Huang Ying <ying.huang@...el.com>
> Cc: Wei Yang <richard.weiyang@...il.com>
> Cc: Mel Gorman <mgorman@...hsingularity.net>
> Signed-off-by: David Hildenbrand <david@...hat.com>

Looks good to me.

Acked-by: Dan Williams <dan.j.williams@...el.com>