On Tue, 2019-06-18 at 22:51 -0700, Dan Williams wrote: > In preparation for sub-section hotplug, track whether a given section > was created during early memory initialization, or later via memory > hotplug. This distinction is needed to maintain the coarse > expectation > that pfn_valid() returns true for any pfn within a given section even > if > that section has pages that are reserved from the page allocator. > > For example one of the of goals of subsection hotplug is to support > cases where the system physical memory layout collides System RAM and > PMEM within a section. Several pfn_valid() users expect to just check > if > a section is valid, but they are not careful to check if the given > pfn > is within a "System RAM" boundary and instead expect pgdat > information > to further validate the pfn. > > Rather than unwind those paths to make their pfn_valid() queries more > precise a follow on patch uses the SECTION_IS_EARLY flag to maintain > the > traditional expectation that pfn_valid() returns true for all early > sections. > > Link: https://lore.kernel.org/lkml/1560366952-10660-1-git-send-email- > cai@xxxxxx/ > Reported-by: Qian Cai <cai@xxxxxx> > Cc: Michal Hocko <mhocko@xxxxxxxx> > Cc: Logan Gunthorpe <logang@xxxxxxxxxxxx> > Cc: David Hildenbrand <david@xxxxxxxxxx> > Cc: Oscar Salvador <osalvador@xxxxxxx> > Cc: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx> > Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx> [...] > @@ -731,7 +732,7 @@ int __meminit sparse_add_one_section(int nid, > unsigned long start_pfn, > page_init_poison(memmap, sizeof(struct page) * > PAGES_PER_SECTION); > > section_mark_present(ms); > - sparse_init_one_section(ms, section_nr, memmap, usage); > + sparse_init_one_section(ms, section_nr, memmap, usage, 0); I think this is an improvment, and I really like the idea of leveraring a new section's flag for this, but I have mixed feelings about the way to mark a section as an early one. IMHO, I think that a new "section_mark_early" function would be better than passing a new flag parameter to sparse_init_one_section(). But I do not feel strong on this: Reviewed-by: Oscar Salvador <osalvador@xxxxxxx> -- Oscar Salvador SUSE L3
