From: Michal Hocko <mhocko@suse.com>
To: Oscar Salvador <osalvador@suse.de>
Cc: david@redhat.com, linux-kernel@vger.kernel.org,
linux-mm@kvack.org, vbabka@suse.cz, pasha.tatashin@soleen.com
Subject: Re: [RFC PATCH v2 3/4] mm,memory_hotplug: Add mhp_supports_memmap_on_memory
Date: Fri, 27 Nov 2020 16:02:53 +0100 [thread overview]
Message-ID: <20201127150253.GU31550@dhcp22.suse.cz> (raw)
In-Reply-To: <20201125112048.8211-4-osalvador@suse.de>
On Wed 25-11-20 12:20:47, Oscar Salvador wrote:
> mhp_supports_memmap_on_memory is meant to be used by the caller prior
> to hot-adding memory in order to figure out whether it can enable
> MHP_MEMMAP_ON_MEMORY or not.
>
> Enabling MHP_MEMMAP_ON_MEMORY requires:
>
> - CONFIG_SPARSEMEM_VMEMMAP
> - architecture support for altmap
> - hot-added range spans a single memory block
It should also require a tunable (kernel parameter for now but maybe we
will need a more fine grained control later) to enable this explicitly.
Earlier discussions have pointed out that allocating vmemmap from each
section can lead to a sparse memory unsuitable for very large pages.
So I believe this should be an opt in.
Also is there any reason why this cannot be a preparatory patch for the
actual implementation? It would look more natural that way to me.
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2020-11-27 15:02 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-25 11:20 [RFC PATCH v2 0/4] Allocate memmap from hotadded memory (per device) Oscar Salvador
2020-11-25 11:20 ` [RFC PATCH v2 1/4] mm,memory_hotplug: Introduce MHP_MEMMAP_ON_MEMORY Oscar Salvador
2020-11-27 14:59 ` Michal Hocko
2020-11-25 11:20 ` [RFC PATCH v2 2/4] mm,memory_hotplug: Allocate memmap from the added memory range Oscar Salvador
2020-11-27 15:15 ` Michal Hocko
2020-11-30 9:12 ` Oscar Salvador
2020-11-25 11:20 ` [RFC PATCH v2 3/4] mm,memory_hotplug: Add mhp_supports_memmap_on_memory Oscar Salvador
2020-11-27 15:02 ` Michal Hocko [this message]
2020-11-30 8:50 ` Oscar Salvador
2020-11-25 11:20 ` [RFC PATCH v2 4/4] mm,memory_hotplug: Enable MHP_MEMMAP_ON_MEMORY when supported Oscar Salvador
2020-11-27 11:55 ` Oscar Salvador
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