Hi David, ---- On Mon, 11 Jul 2022 22:53:36 +0800 David Hildenbrand <david@xxxxxxxxxx> wrote --- > On 11.07.22 14:24, Li Chen wrote: > > From: Li Chen <lchen@xxxxxxxxxxxxx> > > > > When mhp use sparse_add_section, don't check no-map region, > > so that to allow no-map reserved memory to get struct page > > support. > > > > Signed-off-by: Li Chen <lchen@xxxxxxxxxxxxx> > > Change-Id: I0d2673cec1b66adf695251037a00c240976b226f > > --- > > mm/sparse.c | 4 +++- > > 1 file changed, 3 insertions(+), 1 deletion(-) > > > > diff --git a/mm/sparse.c b/mm/sparse.c > > index 120bc8ea5293..a29cd1e7014f 100644 > > --- a/mm/sparse.c > > +++ b/mm/sparse.c > > @@ -690,7 +690,9 @@ static int fill_subsection_map(unsigned long pfn, unsigned long nr_pages) > > > > if (bitmap_empty(map, SUBSECTIONS_PER_SECTION)) > > rc = -EINVAL; > > - else if (bitmap_intersects(map, subsection_map, SUBSECTIONS_PER_SECTION)) > > + else if (memblock_is_map_memory(PFN_PHYS(pfn)) && > > + bitmap_intersects(map, subsection_map, > > + SUBSECTIONS_PER_SECTION)) > > rc = -EEXIST; > > else > > bitmap_or(subsection_map, map, subsection_map, > > I'm not sure I follow completely what you are trying to achieve. But if > you have to add memblock hacks into mm/sparse.c you're most probably > doing something wrong. > > Please explain why that change is necessary, and why it is safe. In the current sparse memory model, free_area_init will insert all memblock.memory into subsection_map and no-map rmem is also a memblock.memory. So, without this change, fill_subsection_map will return -EEXIST. I would say it's not a good idea to insert no-map memblock into subsection_map, and I have no idea why sparse do this. So, I simply skip no-map region here. As for safety: 1. The caller of fill_subsection_map are mhp and *_memremap_pages functions, no-map regions are not related to them, so existing codes won't be broken. 2. This change doesn't change memblock and subsection_map. > > If the subsection map already spans memory (iow, subsection map is set) > you intend to add, then something already added memory in that range? No matter with or without this patch, fill_subsection_map will always return -EEXIST for mapped memory, so that's not a problem. The key point here is I allowed no-map region to pass the check and didn't change anything to the mapped region. Regards, Li
