linux-kernel - Re: [PATCH v2 27/29] mm/memory_hotplug: extend offline_and_remove_memory() to handle more than one memory block

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Message-Id: <20201117205301.bcef9773f3557a764d17b8df@linux-foundation.org>
Date:   Tue, 17 Nov 2020 20:53:01 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     David Hildenbrand <david@...hat.com>
Cc:     linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, linux-mm@...ck.org,
        "Michael S . Tsirkin" <mst@...hat.com>,
        Wei Yang <richard.weiyang@...ux.alibaba.com>,
        Jason Wang <jasowang@...hat.com>,
        Pankaj Gupta <pankaj.gupta.linux@...il.com>,
        Michal Hocko <mhocko@...nel.org>,
        Oscar Salvador <osalvador@...e.de>
Subject: Re: [PATCH v2 27/29] mm/memory_hotplug: extend
 offline_and_remove_memory() to handle more than one memory block

On Thu, 12 Nov 2020 14:38:13 +0100 David Hildenbrand <david@...hat.com> wrote:

> virtio-mem soon wants to use offline_and_remove_memory() memory that
> exceeds a single Linux memory block (memory_block_size_bytes()). Let's
> remove that restriction.
> 
> Let's remember the old state and try to restore that if anything goes
> wrong. While re-onlining can, in general, fail, it's highly unlikely to
> happen (usually only when a notifier fails to allocate memory, and these
> are rather rare).
> 
> This will be used by virtio-mem to offline+remove memory ranges that are
> bigger than a single memory block - for example, with a device block
> size of 1 GiB (e.g., gigantic pages in the hypervisor) and a Linux memory
> block size of 128MB.
> 
> While we could compress the state into 2 bit, using 8 bit is much
> easier.
> 
> This handling is similar, but different to acpi_scan_try_to_offline():
> 
> a) We don't try to offline twice. I am not sure if this CONFIG_MEMCG
> optimization is still relevant - it should only apply to ZONE_NORMAL
> (where we have no guarantees). If relevant, we can always add it.
> 
> b) acpi_scan_try_to_offline() simply onlines all memory in case
> something goes wrong. It doesn't restore previous online type. Let's do
> that, so we won't overwrite what e.g., user space configured.
> 
> ...
>

uint8_t is a bit of a mouthful.  u8 is less typing ;)  Doesn't matter.

Acked-by: Andrew Morton <akpm@...ux-foundation.org>