• Xunlei Pang's avatar
    x86/mm: Add support for gbpages to kernel_ident_mapping_init() · 66aad4fd
    Xunlei Pang authored
    Kernel identity mappings on x86-64 kernels are created in two
    ways: by the early x86 boot code, or by kernel_ident_mapping_init().
    Native kernels (which is the dominant usecase) use the former,
    but the kexec and the hibernation code uses kernel_ident_mapping_init().
    There's a subtle difference between these two ways of how identity
    mappings are created, the current kernel_ident_mapping_init() code
    creates identity mappings always using 2MB page(PMD level) - while
    the native kernel boot path also utilizes gbpages where available.
    This difference is suboptimal both for performance and for memory
    usage: kernel_ident_mapping_init() needs to allocate pages for the
    page tables when creating the new identity mappings.
    This patch adds 1GB page(PUD level) support to kernel_ident_mapping_init()
    to address these concerns.
    The primary advantage would be better TLB coverage/performance,
    because we'd utilize 1GB TLBs instead of 2MB ones.
    It is also useful for machines with large number of memory to
    save paging structure allocations(around 4MB/TB using 2MB page)
    when setting identity mappings for all the memory, after using
    1GB page it will consume only 8KB/TB.
    ( Note that this change alone does not activate gbpages in kexec,
      we are doing that in a separate patch. )
    Signed-off-by: default avatarXunlei Pang <xlpang@redhat.com>
    Cc: Andy Lutomirski <luto@kernel.org>
    Cc: Borislav Petkov <bp@alien8.de>
    Cc: Brian Gerst <brgerst@gmail.com>
    Cc: Dave Young <dyoung@redhat.com>
    Cc: Denys Vlasenko <dvlasenk@redhat.com>
    Cc: Eric Biederman <ebiederm@xmission.com>
    Cc: H. Peter Anvin <hpa@zytor.com>
    Cc: Josh Poimboeuf <jpoimboe@redhat.com>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: Yinghai Lu <yinghai@kernel.org>
    Cc: akpm@linux-foundation.org
    Cc: kexec@lists.infradead.org
    Link: http://lkml.kernel.org/r/1493862171-8799-1-git-send-email-xlpang@redhat.comSigned-off-by: default avatarIngo Molnar <mingo@kernel.org>
hibernate_64.c 8.08 KB