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Date:   Wed, 16 Sep 2020 20:50:41 +0200
From:   osalvador@suse.de
To:     David Hildenbrand <david@redhat.com>
Cc:     linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        linux-hyperv@vger.kernel.org, xen-devel@lists.xenproject.org,
        linux-acpi@vger.kernel.org,
        Andrew Morton <akpm@linux-foundation.org>,
        Alexander Duyck <alexander.h.duyck@linux.intel.com>,
        Dave Hansen <dave.hansen@intel.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        "K. Y. Srinivasan" <kys@microsoft.com>,
        Mel Gorman <mgorman@techsingularity.net>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Michal Hocko <mhocko@kernel.org>,
        Mike Rapoport <rppt@kernel.org>,
        Scott Cheloha <cheloha@linux.ibm.com>,
        Stephen Hemminger <sthemmin@microsoft.com>,
        Vlastimil Babka <vbabka@suse.cz>, Wei Liu <wei.liu@kernel.org>,
        Wei Yang <richard.weiyang@linux.alibaba.com>
Subject: Re: [PATCH RFC 0/4] mm: place pages to the freelist tail when onling
 and undoing isolation
In-Reply-To: <20200916183411.64756-1-david@redhat.com>
References: <20200916183411.64756-1-david@redhat.com>
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On 2020-09-16 20:34, David Hildenbrand wrote:
> When adding separate memory blocks via add_memory*() and onlining them
> immediately, the metadata (especially the memmap) of the next block 
> will be
> placed onto one of the just added+onlined block. This creates a chain
> of unmovable allocations: If the last memory block cannot get
> offlined+removed() so will all dependant ones. We directly have 
> unmovable
> allocations all over the place.
> 
> This can be observed quite easily using virtio-mem, however, it can 
> also
> be observed when using DIMMs. The freshly onlined pages will usually be
> placed to the head of the freelists, meaning they will be allocated 
> next,
> turning the just-added memory usually immediately un-removable. The
> fresh pages are cold, prefering to allocate others (that might be hot)
> also feels to be the natural thing to do.
> 
> It also applies to the hyper-v balloon xen-balloon, and ppc64 dlpar: 
> when
> adding separate, successive memory blocks, each memory block will have
> unmovable allocations on them - for example gigantic pages will fail to
> allocate.
> 
> While the ZONE_NORMAL doesn't provide any guarantees that memory can 
> get
> offlined+removed again (any kind of fragmentation with unmovable
> allocations is possible), there are many scenarios (hotplugging a lot 
> of
> memory, running workload, hotunplug some memory/as much as possible) 
> where
> we can offline+remove quite a lot with this patchset.

Hi David,

I did not read through the patchset yet, so sorry if the question is 
nonsense, but is this not trying to fix the same issue the vmemmap 
patches did? [1]

I was about to give it a new respin now that thw hwpoison stuff has been 
settled.

[1] https://patchwork.kernel.org/cover/11059175/
>