On 06/09/2023 19:10, Mike Kravetz wrote:
On 09/06/23 12:26, Usama Arif wrote:
The new boot flow when it comes to initialization of gigantic pages
is as follows:
- At boot time, for a gigantic page during __alloc_bootmem_hugepage,
the region after the first struct page is marked as noinit.
- This results in only the first struct page to be
initialized in reserve_bootmem_region. As the tail struct pages are
not initialized at this point, there can be a significant saving
in boot time if HVO succeeds later on.
- Later on in the boot, the head page is prepped and the first
HUGETLB_VMEMMAP_RESERVE_SIZE / sizeof(struct page) - 1 tail struct pages
are initialized.
- HVO is attempted. If it is not successful, then the rest of the
tail struct pages are initialized. If it is successful, no more
tail struct pages need to be initialized saving significant boot time.
Code looks reasonable. Quick question.
On systems where HVO is disabled, we will still go through this new boot
flow and init hugetlb tail pages later in boot (gather_bootmem_prealloc).
Correct?
If yes, will there be a noticeable change in performance from the current
flow with HVO disabled? My concern would be allocating a large number of
gigantic pages at boot (TB or more).
Thanks for the review.
The patch moves the initialization of struct pages backing hugepage from
reserve_bootmem_region to a bit later on in the boot to
gather_bootmem_prealloc. When HVO is disabled, there will be no
difference in time taken to boot with or without this patch series, as
262144 struct pages per gigantic page (for x86) are still going to be
initialized, just in a different place.
