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    SubjectRe: [PATCH] mm: hugetlb: don't zero 1GiB bootmem pages.
    On Tue 10-07-18 13:46:57, Mike Kravetz wrote:
    > On 07/10/2018 11:49 AM, Cannon Matthews wrote:
    > > When using 1GiB pages during early boot, use the new
    > > memblock_virt_alloc_try_nid_raw() function to allocate memory without
    > > zeroing it. Zeroing out hundreds or thousands of GiB in a single core
    > > memset() call is very slow, and can make early boot last upwards of
    > > 20-30 minutes on multi TiB machines.
    > >
    > > To be safe, still zero the first sizeof(struct boomem_huge_page) bytes
    > > since this is used a temporary storage place for this info until
    > > gather_bootmem_prealloc() processes them later.
    > >
    > > The rest of the memory does not need to be zero'd as the hugetlb pages
    > > are always zero'd on page fault.
    > >
    > > Tested: Booted with ~3800 1G pages, and it booted successfully in
    > > roughly the same amount of time as with 0, as opposed to the 25+
    > > minutes it would take before.
    > >
    >
    > Nice improvement!
    >
    > > Signed-off-by: Cannon Matthews <cannonmatthews@google.com>
    > > ---
    > > mm/hugetlb.c | 7 ++++++-
    > > 1 file changed, 6 insertions(+), 1 deletion(-)
    > >
    > > diff --git a/mm/hugetlb.c b/mm/hugetlb.c
    > > index 3612fbb32e9d..c93a2c77e881 100644
    > > --- a/mm/hugetlb.c
    > > +++ b/mm/hugetlb.c
    > > @@ -2101,7 +2101,7 @@ int __alloc_bootmem_huge_page(struct hstate *h)
    > > for_each_node_mask_to_alloc(h, nr_nodes, node, &node_states[N_MEMORY]) {
    > > void *addr;
    > >
    > > - addr = memblock_virt_alloc_try_nid_nopanic(
    > > + addr = memblock_virt_alloc_try_nid_raw(
    > > huge_page_size(h), huge_page_size(h),
    > > 0, BOOTMEM_ALLOC_ACCESSIBLE, node);
    > > if (addr) {
    > > @@ -2109,7 +2109,12 @@ int __alloc_bootmem_huge_page(struct hstate *h)
    > > * Use the beginning of the huge page to store the
    > > * huge_bootmem_page struct (until gather_bootmem
    > > * puts them into the mem_map).
    > > + *
    > > + * memblock_virt_alloc_try_nid_raw returns non-zero'd
    > > + * memory so zero out just enough for this struct, the
    > > + * rest will be zero'd on page fault.
    > > */
    > > + memset(addr, 0, sizeof(struct huge_bootmem_page));
    >
    > This forced me to look at the usage of huge_bootmem_page. It is defined as:
    > struct huge_bootmem_page {
    > struct list_head list;
    > struct hstate *hstate;
    > #ifdef CONFIG_HIGHMEM
    > phys_addr_t phys;
    > #endif
    > };
    >
    > The list and hstate fields are set immediately after allocating the memory
    > block here and elsewhere. However, I can't find any code that sets phys.
    > Although, it is potentially used in gather_bootmem_prealloc(). It appears
    > powerpc used this field at one time, but no longer does.
    >
    > Am I missing something?

    If yes, then I am missing it as well. phys is a cool name to grep for...
    Anyway, does it really make any sense to allow gigantic pages on HIGHMEM
    systems in the first place?

    --
    Michal Hocko
    SUSE Labs

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