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From "Dunkin, Nick" <Nick.Dun...@ccur.com>
Subject Re: Understanding ioBufAllocator behvaiour
Date Wed, 24 May 2017 18:52:06 GMT
Hi again,

This is great stuff, but it leads me to believe that I’ve totally overestimated my ram_cache.size
setting.  And in fact, totally misunderstood the parameter.

Let me see if I understand what you’ve explained:

If I expect 5 of my ioBufAllocators to be in use during normal activity, then potentially
I could see memory allocated to the level of (5 x ram_cache.size)?  Because each ioBufAllocator
is bounded by ram_cache.size?

In which case I need to reduce, or tune, my ram_cache.size by a factor of 5?

I have a large ram_cache.size (100gb), assuming it was allocated to one large reserve of memory,
so I assume this understanding is naive?

Thanks again for all your assistance,

Nick

From: "Kapil Sharma (kapsharm)" <kapsharm@cisco.com>
Reply-To: "users@trafficserver.apache.org" <users@trafficserver.apache.org>
Date: Wednesday, May 24, 2017 at 11:29 AM
To: "users@trafficserver.apache.org" <users@trafficserver.apache.org>
Subject: Re: Understanding ioBufAllocator behvaiour

On plateauing - not necessarily; we do see the memory consumption increasing continuously
in our deployments as well. It depends on the pattern of segment sizes over time.

ATS uses power of 2 allocators for memory pool - there are 15 of those, ranging from 128bytes
to 2M if my memory serves me right - and these are per thread! ATS will choose an optimal
allocator for the segments.

As Alan mentioned, once chunk are allocated, they are never freed.

Here is a totally artificial example just to make the point (please correct if my understanding
is flawed):
* the traffic pattern was such that initially only 2M allocators were used then ATS will keep
allocating 2M chunks until RAM cache limit (lets say it is 64GB) is reached.
* Now traffic pattern changed (smaller fragment requests), and only 1M allocators are used,
ATS will now keep allocating 1M chunks, again capping at 64GB. But in the end ATS would have
allocated 128GB well over RAM cache size limit….


In the past a there was some prototype of reclaimable buffer support added in ATS, but I believe
it was removed in 7.0? Also there is recent discussion of adding jmalloc?



On May 24, 2017, at 11:01 AM, Alan Carroll <solidwallofcode@yahoo-inc.com<mailto:solidwallofcode@yahoo-inc.com>>
wrote:

One issue is that memory never moves between the iobuf sizes. Once a chunk of memory is used
for a specific iobuf slot, it's there forever. But unless something is leaking, the total
size should eventually plateau, certainly within less than a day if you have a basically constant
load. There will be some growth due to blocks being kept in thread local allocation pools,
but again that should level in less time than you've run.


On Wednesday, May 24, 2017, 9:50:39 AM CDT, Dunkin, Nick <Nick.Dunkin@ccur.com<mailto:Nick.Dunkin@ccur.com>>
wrote:

Hi Alan,


This is 7.0.0


I only see this behavior on ioBufAllocator[0], [4] and [5].  The other ioBufAllocators’
usage looks as I would expect (i.e. allocated goes up then flat), so I was thinking it was
more likely something to do with my configuration or use-case.


I’d also just like to understand, at a high level, how the ioBufAllocators are used.


Thanks,


Nick


From: Alan Carroll <solidwallofcode@yahoo-inc.com<mailto:solidwallofcode@yahoo-inc.com>>
Reply-To: "users@trafficserver.apache.org<mailto:users@trafficserver.apache.org>" <users@trafficserver.apache.org<mailto:users@trafficserver.apache.org>>
Date: Wednesday, May 24, 2017 at 10:33 AM
To: "users@trafficserver.apache.org<mailto:users@trafficserver.apache.org>" <users@trafficserver.apache.org<mailto:users@trafficserver.apache.org>>
Subject: Re: Understanding ioBufAllocator behvaiour


Honestly it sounds like a leak. Can you specify which version of Traffic Server this is?



On Wednesday, May 24, 2017, 8:22:46 AM CDT, Dunkin, Nick <Nick.Dunkin@ccur.com<mailto:Nick.Dunkin@ccur.com>>
wrote:

Hi


I have a load test that I’ve been running for a number of days now.  I’m using the memory
dump logging in traffic.out and I’m trying to understand how Traffic Server allocates and
reuses memory.  I’m still quite new to Traffic Server.


Nearly all of the memory traces look as I would expect, i.e. memory is allocated and reused
over the lifetime of the test.  However my readings from ioBufAllocator[0] show a continual
increase in allocated AND used.  I am attaching a graph.  (FYI – This graph covers approximately
3 days of continual load test.)


I would have expected to start seeing reuse in ioBufAllocator by now, like I do in the other
ioBufAllocators.  Can someone help me understand what I’m seeing?


Many thanks,


Nick Dunkin


Nick Dunkin

Principal Engineer

o:   678.258.4071

e:   Nick.Dunkin@curr.com<mailto:Nick.Dunkin@ccur.com>

4375 River Green Pkwy # 100, Duluth, GA 30096, USA

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