From: "Aneesh Kumar K.V" <aneesh.kumar@linux•vnet.ibm.com>
To: Anshuman Khandual <khandual@linux•vnet.ibm.com>,
linuxppc-dev@lists•ozlabs.org
Subject: Re: [RFC] KVM: PPC: Book3S HV: Fall back to same size HPT in allocation ioctl
Date: Mon, 12 Sep 2016 17:35:28 +0530 [thread overview]
Message-ID: <8760q1pblj.fsf@linux.vnet.ibm.com> (raw)
In-Reply-To: <1473678797-22069-1-git-send-email-khandual@linux.vnet.ibm.com>
Anshuman Khandual <khandual@linux•vnet.ibm.com> writes:
> When the HPT size is explicitly passed on from the userspace, currently
> the KVM_PPC_ALLOCATE_HTAB will try to allocate the requested size of HPT
> from reserved CMA area and if that is not possible, the allocation just
> fails. With the commit 572abd563befd56 ("KVM: PPC: Book3S HV: Don't fall
> back to smaller HPT size in allocation ioctl"), it does not even try to
> allocate the same order pages from the page allocator before failing for
> good. Same order allocation should be attempted from the page allocator
> as a fallback option when the CMA allocation attempt fails.
IMO we should fix the reason for these CMA allocation failure. We are just
doing work around here.
>
> Signed-off-by: Anshuman Khandual <khandual@linux•vnet.ibm.com>
> ---
> - This change saves guests from failing to start after migration
>
> arch/powerpc/kvm/book3s_64_mmu_hv.c | 8 ++++++++
> 1 file changed, 8 insertions(+)
>
> diff --git a/arch/powerpc/kvm/book3s_64_mmu_hv.c b/arch/powerpc/kvm/book3s_64_mmu_hv.c
> index 05f09ae..0a30eb4 100644
> --- a/arch/powerpc/kvm/book3s_64_mmu_hv.c
> +++ b/arch/powerpc/kvm/book3s_64_mmu_hv.c
> @@ -78,6 +78,14 @@ long kvmppc_alloc_hpt(struct kvm *kvm, u32 *htab_orderp)
> --order;
> }
>
> + /*
> + * Fallback in case the userspace has provided a size via ioctl.
> + * Try allocating the same order pages from the page allocator.
> + */
> + if (!hpt && order > PPC_MIN_HPT_ORDER && htab_orderp)
> + hpt = __get_free_pages(GFP_KERNEL|__GFP_ZERO|__GFP_REPEAT|
> + __GFP_NOWARN, order - PAGE_SHIFT);
> +
> if (!hpt)
> return -ENOMEM;
A better way to do that would be (not even compile tested) ?
diff --git a/arch/powerpc/kvm/book3s_64_mmu_hv.c b/arch/powerpc/kvm/book3s_64_mmu_hv.c
index 65b2b00d93d7..3f8995f27339 100644
--- a/arch/powerpc/kvm/book3s_64_mmu_hv.c
+++ b/arch/powerpc/kvm/book3s_64_mmu_hv.c
@@ -68,16 +68,18 @@ long kvmppc_alloc_hpt(struct kvm *kvm, u32 *htab_orderp)
memset((void *)hpt, 0, (1ul << order));
kvm->arch.hpt_cma_alloc = 1;
}
-
- /* Lastly try successively smaller sizes from the page allocator */
- /* Only do this if userspace didn't specify a size via ioctl */
- while (!hpt && order > PPC_MIN_HPT_ORDER && !htab_orderp) {
+ /*
+ * Try successively smaller sizes from the page allocator.
+ * If a size was specified via an ioctl, we just try that
+ * specific size
+ */
+- while (!hpt && order > PPC_MIN_HPT_ORDER) {
hpt = __get_free_pages(GFP_KERNEL|__GFP_ZERO|__GFP_REPEAT|
__GFP_NOWARN, order - PAGE_SHIFT);
- if (!hpt)
- --order;
+ if (htab_orderp)
+ break;
+ --order;
}
-
if (!hpt)
return -ENOMEM;
next prev parent reply other threads:[~2016-09-12 12:05 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-09-12 11:13 [RFC] KVM: PPC: Book3S HV: Fall back to same size HPT in allocation ioctl Anshuman Khandual
2016-09-12 11:33 ` Balbir Singh
2016-09-13 4:07 ` Anshuman Khandual
2016-09-13 4:34 ` Balbir Singh
2016-09-13 5:49 ` Anshuman Khandual
2016-09-13 9:26 ` Balbir Singh
2016-09-12 12:05 ` Aneesh Kumar K.V [this message]
2016-09-13 6:26 ` Anshuman Khandual
2016-09-13 23:57 ` Michael Ellerman
2016-09-14 0:12 ` Paul Mackerras
2016-09-14 3:55 ` Anshuman Khandual
2016-09-14 3:52 ` Anshuman Khandual
2016-09-14 5:28 ` Anshuman Khandual
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