On 06/14/2015 11:34 PM, Naoya Horiguchi wrote: > On Thu, Jun 11, 2015 at 02:01:37PM -0700, Mike Kravetz wrote: >> Areas hole punched by fallocate will not have entries in the >> region/reserve map. However, shared mappings with min_size subpool >> reservations may still have reserved pages. alloc_huge_page needs >> to handle this special case and do the proper accounting. >> >> Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx> >> --- >> mm/hugetlb.c | 48 +++++++++++++++++++++++++++--------------------- >> 1 file changed, 27 insertions(+), 21 deletions(-) >> >> diff --git a/mm/hugetlb.c b/mm/hugetlb.c >> index ecbaffe..9c295c9 100644 >> --- a/mm/hugetlb.c >> +++ b/mm/hugetlb.c >> @@ -692,19 +692,9 @@ static int vma_has_reserves(struct vm_area_struct *vma, long chg) >> return 0; >> } >> >> - if (vma->vm_flags & VM_MAYSHARE) { >> - /* >> - * We know VM_NORESERVE is not set. Therefore, there SHOULD >> - * be a region map for all pages. The only situation where >> - * there is no region map is if a hole was punched via >> - * fallocate. In this case, there really are no reverves to >> - * use. This situation is indicated if chg != 0. >> - */ >> - if (chg) >> - return 0; >> - else >> - return 1; >> - } >> + /* Shared mappings always use reserves */ >> + if (vma->vm_flags & VM_MAYSHARE) >> + return 1; > > This change completely reverts 5/9, so can you omit 5/9? That was a mistake. This change should not be in the patch. The change from 5/9 needs to remain. Sorry for confusion. Thanks for catching. >> /* >> * Only the process that called mmap() has reserves for >> @@ -1601,6 +1591,7 @@ static struct page *alloc_huge_page(struct vm_area_struct *vma, >> struct hstate *h = hstate_vma(vma); >> struct page *page; >> long chg, commit; >> + long gbl_chg; >> int ret, idx; >> struct hugetlb_cgroup *h_cg; >> >> @@ -1608,24 +1599,39 @@ static struct page *alloc_huge_page(struct vm_area_struct *vma, >> /* >> * Processes that did not create the mapping will have no >> * reserves and will not have accounted against subpool >> - * limit. Check that the subpool limit can be made before >> - * satisfying the allocation MAP_NORESERVE mappings may also >> - * need pages and subpool limit allocated allocated if no reserve >> - * mapping overlaps. >> + * limit. Check that the subpool limit will not be exceeded >> + * before performing the allocation. Allocations for >> + * MAP_NORESERVE mappings also need to be checked against >> + * any subpool limit. >> + * >> + * NOTE: Shared mappings with holes punched via fallocate >> + * may still have reservations, even without entries in the >> + * reserve map as indicated by vma_needs_reservation. This >> + * would be the case if hugepage_subpool_get_pages returns >> + * zero to indicate no changes to the global reservation count >> + * are necessary. In this case, pass the output of >> + * hugepage_subpool_get_pages (zero) to dequeue_huge_page_vma >> + * so that the page is not counted against the global limit. >> + * For MAP_NORESERVE mappings always pass the output of >> + * vma_needs_reservation. For race detection and error cleanup >> + * use output of vma_needs_reservation as well. >> */ >> - chg = vma_needs_reservation(h, vma, addr); >> + chg = gbl_chg = vma_needs_reservation(h, vma, addr); >> if (chg < 0) >> return ERR_PTR(-ENOMEM); >> - if (chg || avoid_reserve) >> - if (hugepage_subpool_get_pages(spool, 1) < 0) >> + if (chg || avoid_reserve) { >> + gbl_chg = hugepage_subpool_get_pages(spool, 1); >> + if (gbl_chg < 0) >> return ERR_PTR(-ENOSPC); >> + } >> >> ret = hugetlb_cgroup_charge_cgroup(idx, pages_per_huge_page(h), &h_cg); >> if (ret) >> goto out_subpool_put; >> >> spin_lock(&hugetlb_lock); >> - page = dequeue_huge_page_vma(h, vma, addr, avoid_reserve, chg); >> + page = dequeue_huge_page_vma(h, vma, addr, avoid_reserve, >> + avoid_reserve ? chg : gbl_chg); > > You use chg or gbl_chg depending on avoid_reserve here, and below this line > there's code like below > > commit = vma_commit_reservation(h, vma, addr); > if (unlikely(chg > commit)) { > ... > } > > This also need to be changed to use chg or gbl_chg depending on avoid_reserve? It should use chg only. I attempted to address this at the end of the Note above. " For race detection and error cleanup use output of vma_needs_reservation as well." I will add more comments to make it clear. > # I feel that this reserve-handling code in alloc_huge_page() is too complicated > # and hard to understand, so some cleanup like separating reserve parts into > # other new routine(s) might be helpful... I agree, let me think about ways to split this up and hopefully make it easier to understand. -- Mike Kravetz > > Thanks, > Naoya Horiguchi > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx"> email@xxxxxxxxx </a>