Hi: On 2021/4/7 8:53, Mike Kravetz wrote: > On 4/2/21 2:32 AM, Miaohe Lin wrote: >> It's guaranteed that the vma is associated with a resv_map, i.e. either >> VM_MAYSHARE or HPAGE_RESV_OWNER, when the code reaches here or we would >> have returned via !resv check above. So ret must be less than 0 in the >> 'else' case. Simplify the return code to make this clear. > > I believe we still neeed that ternary operator in the return statement. > Why? > > There are two basic types of mappings to be concerned with: > shared and private. > For private mappings, a task can 'own' the mapping as indicated by > HPAGE_RESV_OWNER. Or, it may not own the mapping. The most common way > to create a non-owner private mapping is to have a task with a private > mapping fork. The parent process will have HPAGE_RESV_OWNER set, the > child process will not. The idea is that since the child has a COW copy > of the mapping it should not consume reservations made by the parent. The child process will not have HPAGE_RESV_OWNER set because at fork time, we do: /* * Clear hugetlb-related page reserves for children. This only * affects MAP_PRIVATE mappings. Faults generated by the child * are not guaranteed to succeed, even if read-only */ if (is_vm_hugetlb_page(tmp)) reset_vma_resv_huge_pages(tmp); i.e. we have vma->vm_private_data = (void *)0; for child process and vma_resv_map() will return NULL in this case. Or am I missed something? > Only the parent (HPAGE_RESV_OWNER) is allowed to consume the > reservations. > Hope that makens sense? > >> >> Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx> >> --- >> mm/hugetlb.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/mm/hugetlb.c b/mm/hugetlb.c >> index a03a50b7c410..b7864abded3d 100644 >> --- a/mm/hugetlb.c >> +++ b/mm/hugetlb.c >> @@ -2183,7 +2183,7 @@ static long __vma_reservation_common(struct hstate *h, >> return 1; >> } >> else > > This else also handles the case !HPAGE_RESV_OWNER. In this case, we IMO, for the case !HPAGE_RESV_OWNER, we won't reach here. What do you think? > never want to indicate reservations are available. The ternary makes > sure a positive value is never returned. > Many thanks for review and reply! :)
