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SubjectRe: [PATCH] mm: hugetlb: don't zero 1GiB bootmem pages.
On Tue 10-07-18 11:49:03, 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.

The patch makes perfect sense to me. I wasn't even aware that it
zeroying memblock allocation. Thanks for spotting this and fixing it.

> Signed-off-by: Cannon Matthews <cannonmatthews@google.com>

I just do not think we need to to zero huge_bootmem_page portion of it.
It should be sufficient to INIT_LIST_HEAD before list_add. We do
initialize the rest explicitly already.

> ---
> 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));
> m = addr;
> goto found;
> }
> --
> 2.18.0.203.gfac676dfb9-goog

--
Michal Hocko
SUSE Labs

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