From: Oscar Salvador <osalvador@suse.de>
To: David Hildenbrand <david@redhat.com>
Cc: mhocko@kernel.org, linux-kernel@vger.kernel.org,
linux-mm@kvack.org, vbabka@suse.cz, pasha.tatashin@soleen.com
Subject: Re: [RFC PATCH v3 1/4] mm,memory_hotplug: Add mhp_supports_memmap_on_memory
Date: Wed, 9 Dec 2020 10:36:19 +0100 [thread overview]
Message-ID: <20201209093608.GA30590@linux> (raw)
In-Reply-To: <c5b82d52-f1be-0701-e36b-49aae4bb5cdb@redhat.com>
On Wed, Dec 02, 2020 at 10:36:54AM +0100, David Hildenbrand wrote:
> Instead of adding these arch callbacks, what about a config option
>
> ARCH_MHP_MEMMAP_ON_MEMORY_ENABLE
>
> that gets selected by the archs with CONFIG_SPARSEMEM_VMEMMAP ?
>
> The mhp_supports_memmap_on_memory() becomes even more trivial.
I think that would not be enough.
E.g: s390x supports CONFIG_SPARSEMEM_VMEMMAP but it does not support
altmap (and maybe other arches I did not check too).
That is why I was careful in choosing the ones that a) supports
CONFIG_SPARSEMEM_VMEMMAP and b) support altmap
> > Note that mhp_memmap_on_memory kernel boot option will be added in
> > a coming patch.
>
> I think it makes sense to
>
> a) separate off the arch changes into separate patches, clarifying why
> it can be used. Move this patches to the end of the series.
>
> b) Squashing the remainings into patch #2
Ok, I can do that.
> > +/*
> > + * We want memmap (struct page array) to be self contained.
> > + * To do so, we will use the beginning of the hot-added range to build
> > + * the page tables for the memmap array that describes the entire range.
> > + * Only selected architectures support it with SPARSE_VMEMMAP.
>
> You might want to add how the caller can calculate the necessary size
> and that that this calculated piece of memory to be added will be
> accessed before onlining these pages. This is e.g., relevant if
> virtio-mem, the hyper-v balloon, or xen balloon would want to use this
> mechanism. Also, it's somewhat incompatible with standby memory where
> memory cannot be accessed prior to onlining. So pointing that access out
> might be valuable.
Sure, I will be more verbose.
> You can simplify to
>
> return arch_support_memmap_on_memory() &&
> IS_ENABLED(CONFIG_SPARSEMEM_VMEMMAP) &&
> size == memory_block_size_bytes();
Yeah, thanks ;-)
--
Oscar Salvador
SUSE L3
next prev parent reply other threads:[~2020-12-09 9:36 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-01 11:51 [RFC PATCH v3 0/4] Allocate memmap from hotadded memory (per device) Oscar Salvador
2020-12-01 11:51 ` [RFC PATCH v3 1/4] mm,memory_hotplug: Add mhp_supports_memmap_on_memory Oscar Salvador
2020-12-02 9:36 ` David Hildenbrand
2020-12-09 9:36 ` Oscar Salvador [this message]
2020-12-09 9:40 ` David Hildenbrand
2020-12-09 9:43 ` Oscar Salvador
2020-12-01 11:51 ` [RFC PATCH v3 2/4] mm,memory_hotplug: Allocate memmap from the added memory range Oscar Salvador
2020-12-02 10:05 ` David Hildenbrand
2020-12-09 10:32 ` Oscar Salvador
2020-12-09 11:51 ` Oscar Salvador
2020-12-01 11:51 ` [RFC PATCH v3 3/4] mm,memory_hotplug: Enable MHP_MEMMAP_ON_MEMORY when supported Oscar Salvador
2020-12-02 9:37 ` David Hildenbrand
2020-12-09 9:38 ` Oscar Salvador
2020-12-01 11:51 ` [RFC PATCH v3 4/4] mm,memory_hotplug: Add mhp_memmap_on_memory boot option Oscar Salvador
2020-12-02 9:42 ` David Hildenbrand
2020-12-09 10:02 ` Oscar Salvador
2020-12-09 10:04 ` David Hildenbrand
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