On 06/29/22 14:39, Muchun Song wrote: > On Tue, Jun 28, 2022 at 08:40:27AM -0700, James Houghton wrote: > > On Mon, Jun 27, 2022 at 11:42 AM Mike Kravetz <mike.kravetz@xxxxxxxxxx> wrote: > > > > > > On 06/24/22 17:36, James Houghton wrote: > > > > When using HugeTLB high-granularity mapping, we need to go through the > > > > supported hugepage sizes in decreasing order so that we pick the largest > > > > size that works. Consider the case where we're faulting in a 1G hugepage > > > > for the first time: we want hugetlb_fault/hugetlb_no_page to map it with > > > > a PUD. By going through the sizes in decreasing order, we will find that > > > > PUD_SIZE works before finding out that PMD_SIZE or PAGE_SIZE work too. > > > > > > > > > > This may/will cause problems for gigantic hugetlb pages allocated at boot > > > time. See alloc_bootmem_huge_page() where a pointer to the associated hstate > > > is encoded within the allocated hugetlb page. These pages are added to > > > hugetlb pools by the routine gather_bootmem_prealloc() which uses the saved > > > hstate to add prep the gigantic page and add to the correct pool. Currently, > > > gather_bootmem_prealloc is called after hugetlb_init_hstates. So, changing > > > hstate order will cause errors. > > > > > > I do not see any reason why we could not call gather_bootmem_prealloc before > > > hugetlb_init_hstates to avoid this issue. > > > > Thanks for catching this, Mike. Your suggestion certainly seems to > > work, but it also seems kind of error prone. I'll have to look at the > > code more closely, but maybe it would be better if I just maintained a > > separate `struct hstate *sorted_hstate_ptrs[]`, where the original > > I don't think this is a good idea. If you really rely on the order of > the initialization in this patch. The easier solution is changing > huge_bootmem_page->hstate to huge_bootmem_page->hugepagesz. Then we > can use size_to_hstate(huge_bootmem_page->hugepagesz) in > gather_bootmem_prealloc(). > That is a much better solution. Thanks Muchun! -- Mike Kravetz
