Commit 95a5a34d authored by Baoquan He's avatar Baoquan He Committed by Linus Torvalds
Browse files

mm/sparse.c: add note about only VMEMMAP supporting sub-section hotplug 



And tell check_pfn_span() gating the porper alignment and size of hot
added memory region.

And also move the code comments from inside section_deactivate() to being
above it.  The code comments are reasonable for the whole function, and
the moving makes code cleaner.

Signed-off-by: default avatarBaoquan He <bhe@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Reviewed-by: default avatarDavid Hildenbrand <david@redhat.com>
Acked-by: default avatarMichal Hocko <mhocko@suse.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
Cc: Wei Yang <richard.weiyang@gmail.com>
Link: http://lkml.kernel.org/r/20200312124414.439-5-bhe@redhat.com


Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 0a9f9f62

mm/sparse.c

+21 −17
Original line number Diff line number Diff line
@@ -750,6 +750,22 @@ static bool is_subsection_map_empty(struct mem_section *ms) 
}

#endif



/*

 * To deactivate a memory region, there are 3 cases to handle across

 * two configurations (SPARSEMEM_VMEMMAP={y,n}):

 *

 * 1. deactivation of a partial hot-added section (only possible in

 *    the SPARSEMEM_VMEMMAP=y case).

 *      a) section was present at memory init.

 *      b) section was hot-added post memory init.

 * 2. deactivation of a complete hot-added section.

 * 3. deactivation of a complete section from memory init.

 *

 * For 1, when subsection_map does not empty we will not be freeing the

 * usage map, but still need to free the vmemmap range.

 *

 * For 2 and 3, the SPARSEMEM_VMEMMAP={y,n} cases are unified

 */

static void section_deactivate(unsigned long pfn, unsigned long nr_pages,

		struct vmem_altmap *altmap)

{
@@ -760,23 +776,7 @@ static void section_deactivate(unsigned long pfn, unsigned long nr_pages, 


	if (clear_subsection_map(pfn, nr_pages))

		return;

	/*

	 * There are 3 cases to handle across two configurations

	 * (SPARSEMEM_VMEMMAP={y,n}):

	 *

	 * 1/ deactivation of a partial hot-added section (only possible

	 * in the SPARSEMEM_VMEMMAP=y case).

	 *    a/ section was present at memory init

	 *    b/ section was hot-added post memory init

	 * 2/ deactivation of a complete hot-added section

	 * 3/ deactivation of a complete section from memory init

	 *

	 * For 1/, when subsection_map does not empty we will not be

	 * freeing the usage map, but still need to free the vmemmap

	 * range.

	 *

	 * For 2/ and 3/ the SPARSEMEM_VMEMMAP={y,n} cases are unified

	 */



	empty = is_subsection_map_empty(ms);

	if (empty) {

		unsigned long section_nr = pfn_to_section_nr(pfn);
@@ -890,6 +890,10 @@ static struct page * __meminit section_activate(int nid, unsigned long pfn, 
 *

 * This is only intended for hotplug.

 *

 * Note that only VMEMMAP supports sub-section aligned hotplug,

 * the proper alignment and size are gated by check_pfn_span().

 *

 *

 * Return:

 * * 0		- On success.

 * * -EEXIST	- Section has been present.

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