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 LEE9Gj+M 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 08/28/23 19:33, Muchun Song wrote: > > > > On Aug 25, 2023, at 19:18, 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, HVO is attempted. If its successful, only the first > > HUGETLB_VMEMMAP_RESERVE_SIZE / sizeof(struct page) - 1 tail struct pages > > after the head struct page are initialized. If it is not successful, > > then all of the tail struct pages are initialized. > > > > Signed-off-by: Usama Arif > > This edition is simpler than before ever, thanks for your work. > > There is premise that other subsystems do not access vmemmap pages > before the initialization of vmemmap pages associated withe HugeTLB > pages allocated from bootmem for your optimization. However, IIUC, the > compacting path could access arbitrary struct page when memory fails > to be allocated via buddy allocator. So we should make sure that > those struct pages are not referenced in this routine. And I know > if CONFIG_DEFERRED_STRUCT_PAGE_INIT is enabled, it will encounter > the same issue, but I don't find any code to prevent this from > happening. I need more time to confirm this, if someone already knows, > please let me know, thanks. So I think HugeTLB should adopt the similar > way to prevent this. In this patch, the call to hugetlb_vmemmap_optimize() is moved BEFORE __prep_new_hugetlb_folio or prep_new_hugetlb_folio in all code paths. The prep_new_hugetlb_folio routine(s) are what set the destructor (soon to be a flag) that identifies the set of pages as a hugetlb page. So, there is now a window where a set of pages not identified as hugetlb will not have vmemmap pages. Recently, I closed the same window in the hugetlb freeing code paths with commit 32c877191e02 'hugetlb: do not clear hugetlb dtor until allocating'. This patch needs to be reworked so that this window is not opened in the allocation paths. -- Mike Kravetz