PJNATH/ICE Heap Usage Analysis and Optimization
Table of Contents
- How to Calculate the Memory Usage
- Call Setup
- Running with Default Settings
- Optimizing the Memory Usage
- More Optimized Results
- Wait, There's More!
- Final Result
- Crash Course on ICE
This page explains how to analyze the heap usage requirement of PJNATH and how to set various settings to reduce its consumption.
We will use pjsua application for this purpose. All NAT traversal features will be enabled: STUN, ICE, and TURN. The lot.
For the purpose of this article, memory usage of non-PJNATH components will not be shown nor calculated.
The tests were run on a Linux x86_64 machine. The default 64bit alignment may have grown the memory usage slightly. The executable were built with optimizations turned off (because I needed to do some debugging at the same time), but this shouldn't matter to the heap usage I think.
PJSIP version 1.6-trunk was used, r3197 to be exact. Version prior to this didn't have configurable TURN pool memory size.
How to Calculate the Memory Usage
Enter "dd" in pjsua menu to dump all the pools being allocated to the screen/log. For this test though, I've instrumented the application a bit to dump the memory usage at certain points during execution (with pjsip_endpt_dump()) to make the results more consistent.
Calculations were all done in caller side.
$ ./pjsua-x86_64-unknown-linux-gnu --null-audio --max-calls=1 \ --stun-srv=stun.pjsip.org --use-ice \ --dis-codec \* --add-codec pcmu \ --log-file mem.log \ --use-turn --turn-srv=turn.pjsip.org:33478 \ --turn-user xxx --turn-passwd xxx
- has two components (RTP and RTCP) and three candidates (host, STUN, and TURN) for each component in the SDP offer, making a total of six candidates in the offer.
$ /pjsua-x86_64-unknown-linux-gnu --null-audio --local-port 5080 \ --max-calls 1 --use-ice \ --stun-srv=stun.pjsip.org
- has two components (RTP and RTCP) and one host candidate in the SDP answer, making a total of two candidates in the answer.
Memory usage calculations were taken at the following checkpoints:
- Startup, after TURN allocation:
- this will show the initial ICE objects, along with some transmit data buffers for TURN allocation. This checkpoint is not really important.
- After pjsua_start():
- this will show additional objects created by NAT type checker. This would be a good indication on how much peak memory is used during startup.
- Idle after initialization:
- memory usage should have decreased because NAT type checker and initial transmit data buffers would have been cleared. This shows the idle memory usage.
- Right after making outgoing call:
- this will show the additional objects created for the session. There is no special significance of this checkpoint.
- ICE negotiation is complete:
- this would probably show the peak memory usage during a call (and at all times), as many ICE connectivity checks are still kept in memory.
- Warning though: that might not be true. If connectivity checks have been running for a long time (say more than 7 seconds), some objects may have been cleaned.
- 1 minute into call:
- memory usage should decrease as ICE connectivity checks are done. This shows stable memory usage in a call.
- Warning though: TURN was not selected by ICE on this test. When TURN is selected, memory usage will be greater.
Running with Default Settings
Here are the heap usage (of PJNATH objects only) of pjsua, built with default settings, at the above checkpoints:
|1) Startup, after TURN allocation||41,968||58,672||72|
|2) After pjsua_start()||46,728||66,792||70|
|3) Idle after initialization||33,744||46,528||73|
|4) Right after making outgoing call||43,936||61,280||72|
|5) ICE negotiation is complete||55,008||75,960||72|
|6) 1 minute into call||44,568||61,792||72|
I suppose we can improve that!
We'll discuss how we can optimize that below. Read on.
Optimizing the Memory Usage
These methods below only discuss the optimization for PJNATH. For more general memory usage optimization methods, please see footprint discussion in the FAQ.
These are the methods that can be used to reduce memory usage.
Reduce the size of the packet buffers
Each STUN and TURN sockets/sessions would allocate memory buffer, and by default the buffer size is quite big to accommodate wide uses of the library. The savings from reducing these would be significant.
Sample optimized value for the affected settings (and their previous default values in comment):
#define PJ_STUN_SOCK_PKT_LEN (160+200) /* 2000 */ #define PJ_STUN_MAX_PKT_LEN PJ_STUN_SOCK_PKT_LEN /* 800 */ #define PJ_TURN_MAX_PKT_LEN PJ_STUN_MAX_PKT_LEN /* 3000 */
- (160+200): 160 is for 20ms PCMA/PCMU frame, and 200 is for additional STUN/TURN headers in case the frame needs to be transported encapsulated inside STUN/TURN frame (the actual STUN/TURN overhead most likely would be much lower, but I haven't checked the exact size).
- reducing the buffer size will limit how much you can send/receive of course.
Limit the number of ICE candidates, checks, components, etc.
These would affect the ICE's struct size. It probably wouldn't reduce it by much, but still, every bytes count! Sample optimized value for the affected settings (and their default value):
#define PJ_ICE_ST_MAX_CAND 4 /* 8 */ #define PJ_ICE_COMP_BITS 0 /* 1 */ #define PJ_ICE_MAX_CAND (PJ_ICE_ST_MAX_CAND*2) /* 16 */ #define PJ_ICE_MAX_CHECKS (PJ_ICE_ST_MAX_CAND*PJ_ICE_ST_MAX_CAND) /* 32 */
- reducing these constants may cause inability to run on particular hosts (e.g. when there are too many interfaces in the host)
- .. or to talk to certain peers (when they have too many candidates in their SDPs).
Reduce Log Verbosity
Turning off level 5 logging will turn off message tracing in the STUN session, which frees up memory by 1000 bytes per STUN session!
#define PJ_LOG_MAX_LEVEL 4 /* 5 */
Optimize the Pool Size
Using smaller pool sizes would reduce the memory wasted by the pool, at the expense of more calls to malloc(). Each memory pool used by the libraries are tunable, but you would need to experiment with your use case to find out the best size settings for them.
For a very lazy optimization though, just set all pool sizes to 128 (or lower!).
- your app would run slower if you set the pool sizes to smaller values
These are the combined settings based on above methods. You can copy and paste these to your config_site.h:
/* To reduce socket buffers */ #define PJ_STUN_SOCK_PKT_LEN (160+200) /* 2000 */ #define PJ_STUN_MAX_PKT_LEN PJ_STUN_SOCK_PKT_LEN /* 800 */ #define PJ_TURN_MAX_PKT_LEN PJ_STUN_MAX_PKT_LEN /* 3000 */ /* Reduce the size of the respective sessions */ #define PJ_ICE_ST_MAX_CAND 4 /* 8 */ #define PJ_ICE_COMP_BITS 0 /* 1 */ #define PJ_ICE_MAX_CAND (PJ_ICE_ST_MAX_CAND*2) /* 16 */ #define PJ_ICE_MAX_CHECKS (PJ_ICE_ST_MAX_CAND*PJ_ICE_ST_MAX_CAND) /* 32 */ /* Log level < 5 frees up 1000 bytes of buffer in the STUN session! */ #define PJ_LOG_MAX_LEVEL 4 /* 5 */ /* A lazy pool memory usage optimization.. */ # define PJNATH_POOL_LEN_ICE_SESS 128 # define PJNATH_POOL_INC_ICE_SESS 128 # define PJNATH_POOL_LEN_ICE_STRANS 128 # define PJNATH_POOL_INC_ICE_STRANS 128 # define PJNATH_POOL_LEN_NATCK 128 # define PJNATH_POOL_INC_NATCK 128 # define PJNATH_POOL_LEN_STUN_SESS 128 # define PJNATH_POOL_INC_STUN_SESS 128 # define PJNATH_POOL_LEN_STUN_TDATA 128 # define PJNATH_POOL_INC_STUN_TDATA 128 # define PJNATH_POOL_LEN_TURN_SESS 128 # define PJNATH_POOL_INC_TURN_SESS 128 # define PJNATH_POOL_LEN_TURN_SOCK 128 # define PJNATH_POOL_INC_TURN_SOCK 128
More Optimized Results
The result, after using the config_site.h settings above:
|1) App initialization, after TURN allocation||21,488||25,216||85|
|2) After pjsua_start()||24,440||28,800||85|
|3) Idle after initialization||15,568||18,048||86|
|4) Right after making outgoing call||21,032||24,064||87|
|5) After ICE negotiation is complete||25,368||29,312||87|
|6) 1 minute into call||21,464||24,320||88|
Wait, There's More!
If memory constraint is really really tight, there is one more final optimization that we can do, i.e. disabling RTCP, by declaring this macro in config_site.h:
#define PJMEDIA_ADVERTISE_RTCP 0
Since many ICE objects are duplicated across ICE components (RTCP is an ICE component), this could potentially lower the heap usage by half!
While the library currently only provides RTCP for media statistics to assist troubleshooting, still it's quite useful sometimes. You will loose RTT and TX statistics if you disable RTCP (for TX stats, you could get it in the remote endpoint of course). The system designer would need to decide whether this is a feasible optimization.
With RTCP turned off, here are the final result:
|1) App initialization, after TURN allocation||11,264||13,184||85|
|2) After pjsua_start()||14,216||16,768||85|
|3) Idle after initialization||8,304||9,600||87|
|4) Right after making outgoing call||12,800||14,464||88|
|5) After ICE negotiation is complete||18,544||20,992||88|
|6) 1 minute into call||13,136||14,720||89|
It does reduce the heap consumption by close to half in some checkpoints (e.g. when idling after initialization), and significantly reduce the usages on other checkpoints.
We've shown that with the default settings, the peak heap usage per call was around 76 KB, then we reduced it to around 29 KB, then after the final tweak, it's down to around 21 KB only. I think that's not bad!
But please continue reading the warnings below.
- please see all other warnings above
- the number of candidates will vary on each host, hence the memory usages will vary.
- these are just crude experimentations, just to give an idea on how to experiment further
- once again, please bear in mind that we're only optimizing PJNATH here, other settings are left to their default values.
Crash Course on ICE
Let me explain briefly how ICE in PJNATH works, in order to understand where the memory is used. It will be good if you also read the PJNATH manual. For each object mentioned below, I will also give the memory pool name format to recognize them in the memory dump output later, in square brackets. For example, "STUN session [stuntp%p]" means the STUN session is using memory pool which name is formatted with printf like "stuntp%p" format, e.g. "stuntp0x12345678". The value given to the "%p" argument actually is the memory location of the object.
So here it goes.
Objects Created During Startup
ICE Media Transports
These objects are created during PJSUA-LIB initialization, and will be kept alive throughout.
If ICE is enabled, each call will require one PJMEDIA ICE media transport [icetp%d], which in turn creates one ICE stream transport [icetp%d]. Each of these will have two ICE components by default (i.e. RTP and RTCP components). For each component, one STUN socket transport [stuntp%p] and one TURN socket transport [udprel%p] will be created.
The STUN socket transport in turn will create one STUN session. which each will create another pool for incoming packet buffer. All of these use [stuntp%p] pool name format.
Each TURN socket transport creates one TURN session, which in turn create one one STUN session, along with its incoming packet buffer. All of these use [udprel%p] pool name format.
Sample dump output:
.. 19:04:16.888 cachpool icetp00: 344 of 512 (67%) used 19:04:16.888 cachpool icetp00: 1848 of 1920 (96%) used 19:04:16.888 cachpool stuntp0x8218e88: 1248 of 1792 (69%) used 19:04:16.889 cachpool stuntp0x8218e88: 784 of 896 (87%) used 19:04:16.889 cachpool stuntp0x8218e88: 416 of 512 (81%) used 19:04:16.889 cachpool udprel0x822de60: 1184 of 1408 (84%) used 19:04:16.889 cachpool udprel0x822de60: 1816 of 1920 (94%) used 19:04:16.889 cachpool udprel0x822de60: 872 of 896 (97%) used 19:04:16.889 cachpool udprel0x822de60: 368 of 384 (95%) used 19:04:16.889 cachpool stuntp0x822f800: 1248 of 1792 (69%) used 19:04:16.889 cachpool stuntp0x822f800: 784 of 896 (87%) used 19:04:16.889 cachpool stuntp0x822f800: 416 of 512 (81%) used 19:04:16.889 cachpool udprel0x82308e8: 1184 of 1408 (84%) used 19:04:16.889 cachpool udprel0x82308e8: 1816 of 1920 (94%) used 19:04:16.889 cachpool udprel0x82308e8: 872 of 896 (97%) used 19:04:16.889 cachpool udprel0x82308e8: 368 of 384 (95%) used ..
Note that all the above objects are the memory dump of just a single ICE media transport!
NAT Type Checker
The library will also perform NAT type detection to assist NAT related troubleshooting. This test will run briefly (approximately ten seconds), and will be cleaned after that. The NAT type detector's pool format is [natck%p].
Transmit Data Buffers
Each outgoing STUN packet allocates one [tdata%p] pool. Normally these buffers will be kept for few seconds due to retransmissions.
Note: the SIP transmit buffer is named rather similarly: [tdta%p]. Did you notice the difference?
Sample dump of objects related to NAT type checker:
.. 19:04:05.499 cachpool natck0x8233c80: 1200 of 1280 (93%) used 19:04:05.499 cachpool natck0x8233c80: 784 of 896 (87%) used 19:04:05.499 cachpool natck0x8233c80: 416 of 512 (81%) used 19:04:05.499 cachpool tdata0x8234ad0: 888 of 1152 (77%) used 19:04:05.499 cachpool tdata0x8234f70: 888 of 1152 (77%) used 19:04:05.499 cachpool tdata0x822da48: 888 of 1152 (77%) used ..
Did you remember which object is which?
Objects Created During Call
For each call, an ICE session [tdta%p] will be created. Then several individual STUN sessions [stuse%p] will be created, one for each route. Recall that ICE works by pairing every local candidates with each remote candidates, creating N x M possible routes. A mechanism is defined in ICE spec to optimize the number of possible routes, but still, each will need to be checked and each check will require sending a request and waiting for response.
Sample memory dump with three local candidates and two remote candidates:
.. 19:04:33.681 cachpool icetp00: 3928 of 3968 (98%) used 19:04:33.681 cachpool stuse0x8231bd8: 784 of 896 (87%) used 19:04:33.681 cachpool stuse0x82303c0: 376 of 384 (97%) used 19:04:33.687 cachpool stuse0x82304c8: 784 of 896 (87%) used 19:04:33.687 cachpool stuse0x82326b8: 104 of 256 (40%) used 19:04:33.687 cachpool tdata0x822da48: 912 of 1024 (89%) used 19:04:33.687 cachpool tdata0x823f658: 1144 of 1280 (89%) used 19:04:33.687 cachpool tdata0x823fc08: 1144 of 1280 (89%) used 19:04:33.687 cachpool tdata0x82401b8: 1080 of 1280 (84%) used ..