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Message-ID: <557F1C91.9080904@oracle.com>
Date: Mon, 15 Jun 2015 11:42:25 -0700
From: Mike Kravetz <mike.kravetz@...cle.com>
To: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
CC: "linux-mm@...ck.org" <linux-mm@...ck.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Dave Hansen <dave.hansen@...ux.intel.com>,
David Rientjes <rientjes@...gle.com>,
Hugh Dickins <hughd@...gle.com>,
Davidlohr Bueso <dave@...olabs.net>,
Aneesh Kumar <aneesh.kumar@...ux.vnet.ibm.com>,
Hillf Danton <hillf.zj@...baba-inc.com>,
Christoph Hellwig <hch@...radead.org>
Subject: Re: [RFC v4 PATCH 6/9] mm/hugetlb: alloc_huge_page handle areas hole
punched by fallocate
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@...cle.com>
>> ---
>> 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
>
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