Messages in this thread | | | Date | Thu, 16 Aug 2018 16:58:49 +0200 | From | Oscar Salvador <> | Subject | Re: [RFC PATCH 2/3] mm/memory_hotplug: Create __shrink_pages and move it to offline_pages |
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On Thu, Aug 09, 2018 at 12:58:21PM -0400, Jerome Glisse wrote: > I agree, i never thought about that before. Looking at existing resource > management i think the simplest solution would be to use a refcount on the > resources instead of the IORESOURCE_BUSY flags. > > So when you release resource as part of hotremove you would only dec the > refcount and a resource is not busy only when refcount is zero. > > Just the idea i had in mind. Right now i am working on other thing, Oscar > is this something you would like to work on ? Feel free to come up with > something better than my first idea :)
So, I thought a bit about this. First I talked a bit with Jerome about the refcount idea. The problem with reconverting this to refcount is that it is too intrusive, and I think it is not really needed.
I then thought about defining a new flag, something like
#define IORESOURCE_NO_HOTREMOVE xxx
but we ran out of bits for the flag field.
I then thought about doing something like:
struct resource { resource_size_t start; resource_size_t end; const char *name; unsigned long flags; unsigned long desc; struct resource *parent, *sibling, *child; #ifdef CONFIG_MEMORY_HOTREMOVE bool device_managed; #endif };
but it is just too awful, not needed, and bytes consuming.
The only idea I had left is:
register_memory_resource(), which defines a new resource for the added memory-chunk is only called from add_memory(). This function is only being hit when we add memory-chunks.
HMM/devm gets the resources their own way, calling devm_request_mem_region().
So resources that are requested from HMM/devm, have the following flags:
(IORESOURCE_MEM|IORESOURCE_BUSY)
while resources that are requested via mem-hotplug have:
(IORESOURCE_SYSTEM_RAM | IORESOURCE_BUSY)
IORESOURCE_SYSTEM_RAM = (IORESOURCE_MEM|IORESOURCE_SYSRAM)
release_mem_region_adjustable() is only being called from hot-remove path, so unless I am mistaken, all resources hitting that path should match IORESOURCE_SYSTEM_RAM.
That leaves me with the idea that we could check for the resource->flags to contain IORESOURCE_SYSRAM, as I think it is only being set for memory-chunks that are added via memory-hot-add path.
In case it is not, we know that that resource belongs to HMM/devm, so we can back off since they take care of releasing the resource via devm_release_mem_region.
I am working on a RFC v2 containing this, but, Jerome, could you confirm above assumption, please?
Of course, ideas/suggestions are also welcome.
Thanks -- Oscar Salvador SUSE L3
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