From: David Hildenbrand <david@redhat.com>
To: Ben Gardon <bgardon@google.com>, Sean Christopherson <seanjc@google.com>
Cc: LKML <linux-kernel@vger.kernel.org>, kvm <kvm@vger.kernel.org>,
Paolo Bonzini <pbonzini@redhat.com>, Peter Xu <peterx@redhat.com>,
Peter Shier <pshier@google.com>,
Yulei Zhang <yulei.kernel@gmail.com>,
Wanpeng Li <kernellwp@gmail.com>,
Xiao Guangrong <xiaoguangrong.eric@gmail.com>,
Kai Huang <kai.huang@intel.com>,
Keqian Zhu <zhukeqian1@huawei.com>
Subject: Re: [PATCH v4 2/7] KVM: x86/mmu: Factor out allocating memslot rmap
Date: Tue, 11 May 2021 20:56:44 +0200 [thread overview]
Message-ID: <47ba1a62-9035-08c6-22c3-acae9bdd3572@redhat.com> (raw)
In-Reply-To: <CANgfPd9ekAidRzAWi-i=7h0pUpoHADSFJdAB5AWAzwm_Uk3dSA@mail.gmail.com>
On 11.05.21 20:17, Ben Gardon wrote:
> On Tue, May 11, 2021 at 10:56 AM Sean Christopherson <seanjc@google.com> wrote:
>>
>> On Tue, May 11, 2021, Ben Gardon wrote:
>>> Small refactor to facilitate allocating rmaps for all memslots at once.
>>>
>>> No functional change expected.
>>>
>>> Signed-off-by: Ben Gardon <bgardon@google.com>
>>> ---
>>> arch/x86/kvm/x86.c | 39 ++++++++++++++++++++++++++++++---------
>>> 1 file changed, 30 insertions(+), 9 deletions(-)
>>>
>>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>>> index 1e1f4f31e586..cc0440b5b35d 100644
>>> --- a/arch/x86/kvm/x86.c
>>> +++ b/arch/x86/kvm/x86.c
>>> @@ -10911,10 +10911,35 @@ void kvm_arch_free_memslot(struct kvm *kvm, struct kvm_memory_slot *slot)
>>> kvm_page_track_free_memslot(slot);
>>> }
>>>
>>> +static int memslot_rmap_alloc(struct kvm_memory_slot *slot,
>>> + unsigned long npages)
>>> +{
>>> + int i;
>>> +
>>> + for (i = 0; i < KVM_NR_PAGE_SIZES; ++i) {
>>> + int lpages;
>>> + int level = i + 1;
>>> +
>>> + lpages = gfn_to_index(slot->base_gfn + npages - 1,
>>> + slot->base_gfn, level) + 1;
>>
>> Might as well assign lpages at its declaration, i.e.
>>
>> int lpages = gfn_to_index(slot->base_gfn + npages - 1,
>> slot->base_gfn, level) + 1;
>
> I'll do this if I end up sending out a v5.
>
>>> +
>>> + slot->arch.rmap[i] =
>>> + kvcalloc(lpages, sizeof(*slot->arch.rmap[i]),
>>> + GFP_KERNEL_ACCOUNT);
>>
>> Eh, I don't think avoiding a 3 char overrun is worth splitting across three lines.
>> E.g. this is perfectly readable
>>
>> slot->arch.rmap[i] = kvcalloc(lpages, sizeof(*slot->arch.rmap[i]),
>> GFP_KERNEL_ACCOUNT);
>>
>> Alternatively, the rmap size could be captured in a local var, e.g.
>>
>> const int sz = sizeof(*slot->arch.rmap[0]);
>>
>> ...
>>
>> slot->arch.rmap[i] = kvcalloc(lpages, sz, GFP_KERNEL_ACCOUNT);
>
> I like this suggestion. Much nicer. Will incorporate if I send a v5.
>
>> if (!slot->arch.rmap[i]) {
>> memslot_rmap_free(slot);
>> return -ENOMEM;
>> }
>>
>>> + if (!slot->arch.rmap[i]) {
>>> + memslot_rmap_free(slot);
>>> + return -ENOMEM;
>>
>> Reaaaally getting into nitpicks, what do you think about changing this to a goto
>> with the error handling at the bottom? Obviously not necessary by any means,
>> but for me it makes it easier to see that all rmaps are freed on failure. My
>> eyes skipped over that on the first read through. E.g.
>>
>> if (!slot_arch.rmap[i])
>> goto err;
>> }
>>
>> return 0;
>>
>> err:
>> memslot_rmap_free(slot);
>> return -ENOMEM;
>>
>
> Lol, I had a goto in v3, but David Hildenbrand suggested removing it
> and putting the free in the loop. I think I like it more this way too.
No strong opinion, I tend to stick to
Documentation/process/coding-style.rst which states
"The goto statement comes in handy when a function exits from multiple
locations and some common work such as cleanup has to be done."
As we only have a single error exit and no complicated locking, at least
for me the "goto" makes it unnecessary hard to read.
--
Thanks,
David / dhildenb
next prev parent reply other threads:[~2021-05-11 18:56 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-11 17:16 [PATCH v4 0/7] Lazily allocate memslot rmaps Ben Gardon
2021-05-11 17:16 ` [PATCH v4 1/7] KVM: x86/mmu: Deduplicate rmap freeing Ben Gardon
2021-05-11 17:16 ` [PATCH v4 2/7] KVM: x86/mmu: Factor out allocating memslot rmap Ben Gardon
2021-05-11 17:56 ` Sean Christopherson
2021-05-11 18:17 ` Ben Gardon
2021-05-11 18:56 ` David Hildenbrand [this message]
2021-05-11 17:16 ` [PATCH v4 3/7] KVM: mmu: Refactor memslot copy Ben Gardon
2021-05-11 18:47 ` Sean Christopherson
2021-05-11 17:16 ` [PATCH v4 4/7] KVM: mmu: Add slots_arch_lock for memslot arch fields Ben Gardon
2021-05-11 18:55 ` Sean Christopherson
2021-05-11 19:21 ` Sean Christopherson
2021-05-11 19:29 ` Paolo Bonzini
2021-05-11 17:16 ` [PATCH v4 5/7] KVM: x86/mmu: Add a field to control memslot rmap allocation Ben Gardon
2021-05-11 17:16 ` [PATCH v4 6/7] KVM: x86/mmu: Skip rmap operations if rmaps not allocated Ben Gardon
2021-05-11 19:51 ` Sean Christopherson
2021-05-11 17:16 ` [PATCH v4 7/7] KVM: x86/mmu: Lazily allocate memslot rmaps Ben Gardon
2021-05-11 18:57 ` Sean Christopherson
2021-05-11 20:03 ` Sean Christopherson
2021-05-11 20:04 ` Sean Christopherson
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