Message-ID: <f781e5db-cfed-6acf-c844-4825f2336567@redhat.com>
Date:   Thu, 11 Jul 2019 07:37:49 -0400
From:   Nitesh Narayan Lal <nitesh@...hat.com>
To:     Dave Hansen <dave.hansen@...el.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        pbonzini@...hat.com, lcapitulino@...hat.com, pagupta@...hat.com,
        wei.w.wang@...el.com, yang.zhang.wz@...il.com, riel@...riel.com,
        david@...hat.com, mst@...hat.com, dodgen@...gle.com,
        konrad.wilk@...cle.com, dhildenb@...hat.com, aarcange@...hat.com,
        alexander.duyck@...il.com, john.starks@...rosoft.com,
        mhocko@...e.com
Subject: Re: [RFC][PATCH v11 0/2] mm: Support for page hinting


On 7/10/19 4:19 PM, Dave Hansen wrote:
> On 7/10/19 12:51 PM, Nitesh Narayan Lal wrote:
>> This patch series proposes an efficient mechanism for reporting free memory
>> from a guest to its hypervisor. It especially enables guests with no page cache
>> (e.g., nvdimm, virtio-pmem) or with small page caches (e.g., ram > disk) to
>> rapidly hand back free memory to the hypervisor.
>> This approach has a minimal impact on the existing core-mm infrastructure.
>>
>> Measurement results (measurement details appended to this email):
>> *Number of 5GB guests (each touching 4GB memory) that can be launched
>> without swap usage on a system with 15GB:
> This sounds like a reasonable measurement, but I think you're missing a
> sentence or two explaining why this test was used.
I will re-work the cover email to better communicate the numbers.
>
>> unmodified kernel - 2, 3rd with 2.5GB   
> What does "3rd with 2.5GB" mean?  The third gets 2.5GB before failing an
> allocation and crashing?
It doesn't crash or fail. To complete the execution of the test
application which allocates 4GB memory in the 3rd guest 2.5GB swap has
been accessed.
>
>> v11 page hinting - 6, 7th with 26MB    
>> v1 bubble hinting[1] - 6, 7th with 1.8GB (bubble hinting is another series
>> proposed to solve the same problems)
> Could you please make an effort to format things so that reviewers can
> easily read them?  Aligning columns and using common units would be very
> helpful, for instance:
>
>      unmodified kernel - 2, 3rd with 2.50 GB
>       v11 page hinting - 6, 7th with 0.03 GB
>   v1 bubble hinting[1] - 6, 7th with 1.80 GB
>
> See how you can scan that easily and compare between the rows?
>
> I think you did some analysis below.  But, that seems misplaced.  It's
> better to include the conclusion here and the details to back it up
> later.  As it stands, the cover letter just throws some data at a
> reviewer and hopes they can make sense of it.
I will improve this. Thanks.
>
>> *Memhog execution time (For 3 guests each of 6GB on a system with 15GB):
>> unmodified kernel - Guest1:21s, Guest2:27s, Guest3:2m37s swap used = 3.7GB       
>> v11 page hinting - Guest1:23s, Guest2:26s, Guest3:21s swap used = 0           
>> v1 bubble hinting - Guest1:23, Guest2:11s, Guest3:26s swap used = 0           
> Again, I'm finding myself having to reformat your data just so I can
> make sense of it.  You also forgot the unit for Guest 1 in row 3.
>
>    unmodified - Guest1:21s, Guest2:27s, Guest3:2m37s swap used = 3.7GB
>
>   v11 hinting - Guest1:23s, Guest2:26s, Guest3:21s swap used = 0
>   v1 bubble   - Guest1:23s, Guest2:11s, Guest3:26s swap used = 0
>
> So, what is this supposed to show?  What does it mean?  Why do the
> numbers vary *so* much?

Basically, the idea was to communicate that with hinting swap was not
accessed and hence the time of execution is lower.

But as you already mentioned next time around I will format this and add
the conclusion along with these numbers.
I agree with Alexander's comment that there is no point of having the
same thing at two place.

-- 
Thanks
Nitesh

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