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Commit 91eea67c authored by Mark Nelson's avatar Mark Nelson Committed by Benjamin Herrenschmidt
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powerpc/mm: Track backing pages allocated by vmemmap_populate() 



We need to keep track of the backing pages that get allocated by
vmemmap_populate() so that when we use kdump, the dump-capture kernel knows
where these pages are.

We use a simple linked list of structures that contain the physical address
of the backing page and corresponding virtual address to track the backing
pages.
To save space, we just use a pointer to the next struct vmemmap_backing. We
can also do this because we never remove nodes.  We call the pointer "list"
to be compatible with changes made to the crash utility.

vmemmap_populate() is called either at boot-time or on a memory hotplug
operation. We don't have to worry about the boot-time calls because they
will be inherently single-threaded, and for a memory hotplug operation
vmemmap_populate() is called through:
sparse_add_one_section()
            |
            V
kmalloc_section_memmap()
            |
            V
sparse_mem_map_populate()
            |
            V
vmemmap_populate()
and in sparse_add_one_section() we're protected by pgdat_resize_lock().
So, we don't need a spinlock to protect the vmemmap_list.

We allocate space for the vmemmap_backing structs by allocating whole pages
in vmemmap_list_alloc() and then handing out chunks of this to
vmemmap_list_populate().

This means that we waste at most just under one page, but this keeps the code
is simple.

Signed-off-by: default avatarMark Nelson <markn@au1.ibm.com>
Signed-off-by: default avatarBenjamin Herrenschmidt <benh@kernel.crashing.org>
parent 13bb5339

arch/powerpc/include/asm/pgalloc-64.h

+6 −0
Original line number Diff line number Diff line
@@ -11,6 +11,12 @@ 
#include <linux/cpumask.h>

#include <linux/percpu.h>



struct vmemmap_backing {

	struct vmemmap_backing *list;

	unsigned long phys;

	unsigned long virt_addr;

};



/*

 * Functions that deal with pagetables that could be at any level of

 * the table need to be passed an "index_size" so they know how to

arch/powerpc/mm/init_64.c

+43 −0
Original line number Diff line number Diff line
@@ -252,6 +252,47 @@ static void __meminit vmemmap_create_mapping(unsigned long start, 
}

#endif /* CONFIG_PPC_BOOK3E */



struct vmemmap_backing *vmemmap_list;



static __meminit struct vmemmap_backing * vmemmap_list_alloc(int node)

{

	static struct vmemmap_backing *next;

	static int num_left;



	/* allocate a page when required and hand out chunks */

	if (!next || !num_left) {

		next = vmemmap_alloc_block(PAGE_SIZE, node);

		if (unlikely(!next)) {

			WARN_ON(1);

			return NULL;

		}

		num_left = PAGE_SIZE / sizeof(struct vmemmap_backing);

	}



	num_left--;



	return next++;

}



static __meminit void vmemmap_list_populate(unsigned long phys,

					    unsigned long start,

					    int node)

{

	struct vmemmap_backing *vmem_back;



	vmem_back = vmemmap_list_alloc(node);

	if (unlikely(!vmem_back)) {

		WARN_ON(1);

		return;

	}



	vmem_back->phys = phys;

	vmem_back->virt_addr = start;

	vmem_back->list = vmemmap_list;



	vmemmap_list = vmem_back;

}



int __meminit vmemmap_populate(struct page *start_page,

			       unsigned long nr_pages, int node)

{
@@ -276,6 +317,8 @@ int __meminit vmemmap_populate(struct page *start_page, 
		if (!p)

			return -ENOMEM;



		vmemmap_list_populate(__pa(p), start, node);



		pr_debug("      * %016lx..%016lx allocated at %p\n",

			 start, start + page_size, p);