> On Aug 29, 2023, at 05:04, Mike Kravetz <mike.kravetz@xxxxxxxxxx> wrote: > > On 08/28/23 19:33, Muchun Song wrote: >> >> >>> On Aug 25, 2023, at 19:18, Usama Arif <usama.arif@xxxxxxxxxxxxx> 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 <usama.arif@xxxxxxxxxxxxx> >> >> 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. Thanks for your point it out. Seems this issue is not related to this change? hugetlb_vmemmap_optimize() is called before the setting of destructor since the initial commit f41f2ed43ca5. Right? > > Recently, I closed the same window in the hugetlb freeing code paths with > commit 32c877191e02 'hugetlb: do not clear hugetlb dtor until allocating'. Yes, I saw it. > This patch needs to be reworked so that this window is not opened in the > allocation paths. So I think the fix should be a separate series. Thanks.
