On 2016/12/16 2:31, Andrea Reale wrote: > Hi Xishi Qiu, > > thanks for your comments. > > The short anwser to your question is the following. As you hinted, > it is related to the way pfn_valid() is implemented in arm64 when > CONFIG_HAVE_ARCH_PFN_VALID is true (default), i.e., just a check for > the NOMAP flags on the corresponding memblocks. > > Since arch_add_memory->__add_pages() expects pfn_valid() to return false > when it is first called, we mark corresponding memory blocks with NOMAP; > however, arch_add_memory->__add_pages()->__add_section()->__add_zone() > expects pfn_valid() to return true when, at the end of its body, > it cycles through pages to call SetPageReserved(). Since blocks are > marked with NOMAP, pages will not be reserved there, henceforth we > need to reserve them after we clear the NOMAP flag inside the body of > arch_add_memory. Having pages reserved at the end of arch_add_memory > is a preconditions for the upcoming onlining of memory blocks (see > memory_block_change_state()). > >> It's because that in memmap_init_zone() -> early_pfn_valid(), the new page >> is still >> invalid, so we need to init it after memblock_clear_nomap() >> >> So why not use __init_single_page() and set_pageblock_migratetype()? > > About your comment on memmap_init_zone()->early_pfn_valid(), I think > that that particular check is never executed in the context of memory > hotplug; in fact, just before the call to early_pfn_valid(), the code > will jump to the `not_early` label, because the context == MEMMAP_HOPTLUG. >
Hi Andrea, Thanks for your answer, I notice it now. I thought SetPageReserved() was done in memmap_init_zone(), but the new kernel change this logic now, so sorry for the noise. Thanks, Xishi Qiu
