From: Baoquan He <bhe@xxxxxxxxxx> Subject: 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. Link: http://lkml.kernel.org/r/20200312124414.439-5-bhe@xxxxxxxxxx Signed-off-by: Baoquan He <bhe@xxxxxxxxxx> Acked-by: Michal Hocko <mhocko@xxxxxxxx> Reviewed-by: David Hildenbrand <david@xxxxxxxxxx> Cc: Dan Williams <dan.j.williams@xxxxxxxxx> Cc: Pankaj Gupta <pankaj.gupta.linux@xxxxxxxxx> Cc: Wei Yang <richard.weiyang@xxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/sparse.c | 38 +++++++++++++++++++++----------------- 1 file changed, 21 insertions(+), 17 deletions(-) --- a/mm/sparse.c~mm-sparsec-add-note-about-only-vmemmap-supporting-sub-section-hotplug +++ a/mm/sparse.c @@ -750,6 +750,22 @@ static bool is_subsection_map_empty(stru } #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 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_a * * 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. _
