BufferList overhead is too high

RESOLVED FIXED in Firefox 56

Status

()

enhancement
RESOLVED FIXED
2 years ago
2 years ago

People

(Reporter: Ehsan, Assigned: hchang)

Tracking

unspecified
mozilla56
Points:
---
Dependency tree / graph

Firefox Tracking Flags

(firefox56 fixed)

Details

(Whiteboard: [qf:p1])

Attachments

(3 attachments)

Reporter

Description

2 years ago
I was looking at an Instruments profile for imgLoader::Load where there Pickle::WriteBytes is taking more than 30% of the time.  It seems that in many cases, if you consider the memmove cost to be the "meat" of the WriteBytes, there is a lot of overhead in the rest of it.  It seems like in bug 1262671 the trade-off was between using buffers of unequal size to save memory vs buffers of equal size with something like nsSegmentedBuffer.

I'm not really sure I understand all of the details here.  Bill, what do you think?

One thing that *really* hurts us here is the malloc that is in the way here.  We should do whatever we can to not need to malloc in most cases.  On desktop, it seems like we should be able to afford doing that.

Any other improvements we can make to the code you can think of?

BTW, now we have telemetry on this, so if we for example eliminate the malloc, we can see the impact on telemetry.
Flags: needinfo?(wmccloskey)
Reporter

Comment 1

2 years ago
Reporter

Comment 2

2 years ago
Posted image Instruments Profile
You might want to turn off sentinel checking when you measure this:
http://searchfox.org/mozilla-central/rev/c9f5cc6b4593d461e87a6221dc0286b3859fd515/ipc/chromium/src/base/pickle.h#27
It increases the amount of work we do in this code.

Looking at the code for BufferList::WriteBytes, I don't see a lot of fat to trim. We could update mSize for the BufferList all at once instead of inside the loop. That would save a couple additions, which isn't much. Maybe the updates to both |copy| and |remaining| are redundant, but I kinda figured the compiler could deal with those. Maybe it can't. I haven't looked closely at the assembly.

We can't really eliminate the malloc. That's pretty much what this function does: allocate space and copy data into it. We could allocate in bigger chunks, but that means we'll waste more space. I never did much profiling to find a good chunk size. I think I used whatever we had used before.

I doubt SegmentedVector would be more efficient here. It doesn't actually have a method to do what WriteBytes does. If we added one, it would probably do what WriteBytes does.
Flags: needinfo?(wmccloskey)
If we know the approximate size of specific messages, we could use a size that's more appropriate for them. In some cases that could be based on the types being sent (since some are fixed size). I'm not sure about the case in your profile though.
I don't know how much it will help, but maybe you could fix mStandardCapacity as a template argument (it looks like we use 4096 everywhere, except for a borrow method where it is 0 but presumably unused), then split out the last iteration of the loop that has to copy a partial segment, and maybe the compiler can inline the memcpy, which might help. It doesn't seem to have inlined the memcpy in the screenshot Ehsan posted. Maybe just fixing the segment size would be enough for it to decide to do something fancy with the memcpy.
But I guess having a larger chunk size for larger messages is probably a bigger win. The spread of message size is really large...
Reporter

Comment 7

2 years ago
(In reply to Bill McCloskey (:billm) from comment #3)
> You might want to turn off sentinel checking when you measure this:
> http://searchfox.org/mozilla-central/rev/
> c9f5cc6b4593d461e87a6221dc0286b3859fd515/ipc/chromium/src/base/pickle.h#27
> It increases the amount of work we do in this code.

Ugh, can we turn this off in non-debug builds?  We are going to get telemetry on these serialization times, having this turned on will make our numbers misleading.

> Looking at the code for BufferList::WriteBytes, I don't see a lot of fat to
> trim. We could update mSize for the BufferList all at once instead of inside
> the loop. That would save a couple additions, which isn't much. Maybe the
> updates to both |copy| and |remaining| are redundant, but I kinda figured
> the compiler could deal with those. Maybe it can't. I haven't looked closely
> at the assembly.
> 
> We can't really eliminate the malloc. That's pretty much what this function
> does: allocate space and copy data into it. We could allocate in bigger
> chunks, but that means we'll waste more space. I never did much profiling to
> find a good chunk size. I think I used whatever we had used before.
> 
> I doubt SegmentedVector would be more efficient here. It doesn't actually
> have a method to do what WriteBytes does. If we added one, it would probably
> do what WriteBytes does.

Well, my suggestion was having a simple segmented vector with a larger buffer size.  We have telemetry on our IPC message sizes that we can use to pick a smart size.  Does that sound doable?
I think the IPC message size telemetry expired, or is about to expire, so you may need to bump the date on that.
(In reply to :Ehsan Akhgari (busy) from comment #7)
> (In reply to Bill McCloskey (:billm) from comment #3)
> > You might want to turn off sentinel checking when you measure this:
> > http://searchfox.org/mozilla-central/rev/
> > c9f5cc6b4593d461e87a6221dc0286b3859fd515/ipc/chromium/src/base/pickle.h#27
> > It increases the amount of work we do in this code.
> 
> Ugh, can we turn this off in non-debug builds?  We are going to get
> telemetry on these serialization times, having this turned on will make our
> numbers misleading.

I think it does actually catch bugs. We can turn it off for a little while, but it's a valuable assertion. Having it on DEBUG-only isn't very useful. Its purpose is to make weird IPC-related bugs easier to understand.

> Well, my suggestion was having a simple segmented vector with a larger
> buffer size.  We have telemetry on our IPC message sizes that we can use to
> pick a smart size.  Does that sound doable?

We can consider increasing the default segment size. The IPC_MESSAGE_SIZE histogram did expire in 55, but the data from 54 is still around and probably still valid. A bigger problem is that we only count a message in this histogram if the payload is >= 8K. It might be better to add a new histogram (probably one that wouldn't be keyed). I filed bug 1353159 for this.
Whiteboard: [qf]
Whiteboard: [qf] → [qf:investigate:p1]
Reporter

Updated

2 years ago
Depends on: 1353159
Assignee

Updated

2 years ago
Assignee: nobody → hchang
Assignee

Comment 10

2 years ago
I cannot see any data from https://telemetry.mozilla.org/
so I did a very simple local short-term profiling and the 
result is at [1].

PContent::Msg_AccumulateChildKeyedHistograms
PHttpChannel::Msg_OnTransportAndData
PLayerTransaction::Msg_Update
PBrowser::Msg_AsyncMessage
PHttpChannel::Msg_OnStartRequest

seem to be the hotspots. 

Will consult with people who are more familiar with telemetry stuff.

[1] https://docs.google.com/spreadsheets/d/1JiJLPxSpChC9GbyivFDLqHbKNB4QDTzdAmXUflx0YdU/edit?usp=sharing
Reporter

Comment 11

2 years ago
Henry, please recheck telemetry data after bug 1364556 has been fixed.
Assignee

Comment 12

2 years ago
I further analyzed the local profiling data and put it in [1].

In short, 95% of the IPC messages have size less than 4096 and
98% less than 8192.

By message:

                                                        4096    8192   12288	16384	20480	24576	28672
-----------------------------------------------------------------------------------------------------------
PContent::Msg_StoreAndBroadcastBlobURLRegistration	0	100					
PContent::Msg_SetXPCOMProcessAttributes	                0	0	0	0	0	0	0
PHttpChannel::Msg_OnStartRequest	                36	100					
PContent::Msg_AccumulateChildKeyedHistograms	        56	67	74	80	89	93	95
PContent::Msg_AccumulateChildHistograms	                65	67	68	68	69	70	70
PHttpChannel::Msg_OnTransportAndData	                66	90	94	95	98	99	99
PHttpChannel::Msg_Redirect1Begin	                68	100					
PLayerTransaction::Msg_Update                          	76	94	97	99	99	99	99
PNecko::Msg_PHttpChannelConstructor              	79	96	98	99	99	99	99
PWyciwygChannel::Msg_WriteToCacheEntry           	81	92	96	100			
PWyciwygChannel::Msg_SetSecurityInfo             	82	100					
PMessagePort::Msg_PostMessages                   	83	83	100				
PMessagePort::Msg_ReceiveData	                        83	83	100				
PContent::Msg_BroadcastLocalStorageChange	        93	100					
PBackgroundIDBCursor::Msg_Response	                94	94	94	94	94	94	94
PContent::Msg_DispatchLocalStorageChange	        94	100					
PBrowser::Msg_AsyncMessage	                        96	97	99	99	99	99	99

If we set the pre-allocated buffer size to 8192: 

33% of PContent::Msg_AccumulateChildKeyedHistograms
33%    PContent::Msg_AccumulateChildHistograms
10%    PHttpChannel::Msg_OnTransportAndData
6%     PLayerTransaction::Msg_Update
5%     PBackgroundIDBCursor::Msg_Response

will require memory allocation in BufferList::Write().

So, we may either

1) Set 8192  to the pre-allocated buffer size
2) Set 12288 to the pre-allocated buffer size
3) Set 8192 as the pre-allocated size and specialize a size for
   Msg_OnTransportAndData and PLayerTransaction::Msg_Update since they
   seem to popular enough to have a custom size.



[1] https://docs.google.com/spreadsheets/d/1qYpO4vBL2cPHWvHLZhjtAJR_HRGKeQNYSVmgzRUO9PE/edit#gid=1353915496
Assignee

Comment 13

2 years ago
Hi Eshan,

According to comment 12, would you like me to change the default
preallocated size to 8192 first or we should still wait for the
actual telemetry data?

Thanks!
Flags: needinfo?(ehsan)
Reporter

Comment 14

2 years ago
Hmm, I think I would probably get the telemetry data since I think getting a good breadth over all messages that we should care about may be difficult with some local testing, but I'm curious to know what Bill thinks here (and since he knows a lot more about IPC than I do, his opinion should probably override mine here!).

If we decide to just use your local testing, option 3 in comment 12 looks really good to me based on the data at hand!

Thanks a lot for digging through this so far.  :-)
Flags: needinfo?(ehsan)
Assignee

Comment 15

2 years ago
The telemetry I added in bug 1353159 in comparison with my local analysis 
lacks the global distribution and the per-message distribution. I am not
so sure if they would become important in the end. 

I might firstly work on being able to have custom preallocated buffer size
given that some messages do have outstanding message size.
Assignee

Comment 16

2 years ago
There seem to be the following approaches to have custom preallocation size
based on message type:

1) Templatize IPC::Message by "message id". (IPC::Message inherits Pickle, which owns
   the BufferList.) This requires the change of IPDL codegen to generate code like
   
   return new IPC::Message<PAPZCTreeManager:Msg_UpdateZoomConstraints__ID>(routingId, Msg_UpdateZoomConstraints__ID, ...

   If we don't want to increase the code size too much, we can have default template 
   parameter for those message types which don't need to be customized.

2) Just dynamically determine the default preallocation size in like 

http://searchfox.org/mozilla-central/rev/f55349994fdac101d121b11dac769f3f17fbec4b/ipc/chromium/src/base/pickle.cc#140

One thing I wanted to point out is in which layer we should specify the 
custom message size. If we do not do it in the "*.ipdl", we have to 
hardcode the generated message id. I don't know if this would be an
issue.

Hi Bill, 

may I know your feedback about comment 12 and the approaches to have
custom preallocation size? Thanks!
Assignee

Updated

2 years ago
Flags: needinfo?(wmccloskey)
I'm now wishing that we had counted every message in bug 1353159, not just the ones over 4K. I should have realized that it makes the histogram useless for deciding whether 4K is a good size. The main thing I noticed from comment 12 is:

> In short, 95% of the IPC messages have size less than 4096 and
> 98% less than 8192.

That suggests to me that we should not increase the default size at all. If we did, then the space would be wasted in 95% of cases and we would avoid an allocation in 3% of cases. That doesn't seem like a good trade-off at all!

However, using custom message sizes for certain important messages seems fine to me. I think option (2) from comment 16 is the right way to do it. I would recommend having a .ini file to store the sizes in, sort of like how we have sync-messages.ini.
Flags: needinfo?(wmccloskey)
I think we have enough data so I'm changing this to qf:p1
Whiteboard: [qf:investigate:p1] → [qf:p1]
Assignee

Comment 19

2 years ago
Telemetry data is out:

https://telemetry.mozilla.org/new-pipeline/dist.html#!cumulative=1&end_date=2017-05-21&keys=__none__!__none__!__none__&max_channel_version=nightly%252F55&measure=IPC_MESSAGE_SIZE2&min_channel_version=null&processType=*&product=Firefox&sanitize=1&sort_keys=submissions&start_date=2017-05-10&table=0&trim=1&use_submission_date=0

but it only has message sizes >= 4096 bytes,

Assume the Prob(size < 4096) is 95% (according to comment 12%), then the normalized
cumulative distribution should be 

P'(size < X) = 95% + P(size < X) * 5%, 

where P(x) is the probability from the telemetry and P'(x) is the normalized one.

95%   < 4k
97.3% < 9.43k
97.7% < 12.99k
98.9% < 17.92k
Reporter

Comment 20

2 years ago
Ping? Has there been any activity here?
Assignee

Comment 21

2 years ago
(In reply to :Ehsan Akhgari (needinfo please, extremely long backlog) from comment #20)
> Ping? Has there been any activity here?

Sorry I am working on bug 1355746 and bug 1349255 lately. This is
the next one in my queue. Should I escalate its priority over others?

BTW, I am going to take the *.ini* approach which mentioned in comment 17,
which means I will have to modify the ipdl parser but it shouldn't be 
a big deal.

Thanks :)
Reporter

Comment 22

2 years ago
(In reply to Henry Chang [:hchang] from comment #21)
> (In reply to :Ehsan Akhgari (needinfo please, extremely long backlog) from
> comment #20)
> > Ping? Has there been any activity here?
> 
> Sorry I am working on bug 1355746 and bug 1349255 lately. This is
> the next one in my queue. Should I escalate its priority over others?

Nope, just checking.  Thanks a lot!  :-)
Assignee

Comment 23

2 years ago
I have almost done Bug 1355746 and hope to discuss bug 1349255 with 
Masayuki san in person. So, I will be working on this one lately and
probably be able to get reviewed and landed in the work week.
Comment hidden (mozreview-request)
Assignee

Comment 26

2 years ago
Hi Bill,

I have followed your suggestion and had a WIP patch designed as the following:

1) message-sizes.ini to descibe messages and their sizes which we'd 
   like to have custom initial BufferList capacity for serialization.
   The .ini looks like

[PContent::AccumulateChildKeyedHistograms]
size = 16384
[PContent::AccumulateChildHistograms]
size = 16384
[PLayerTransaction::Update]
size = 8192

2) Modify ipdl.py, lower.py and etc to generate a .inc file like the follwing
   based on message-sizes.ini

{ {mozilla::dom::PContent::AccumulateChildKeyedHistograms, 16384} },
{ {mozilla::dom::PContent::AccumulateChildKeyedHistograms, 16384} },
{ {mozilla::layers::PLayerTransaction, 8192} },

3) Modify ipc_message.h/cc and pickle.h/cc to use the custom default
   chunkc size based on the message id (according to the generated code)

Do you think if my above approach on the right track? For example, would you
prefer generating a header file instead of just a section of code? Would you
like me to figure out how to generate code to list all header files which
are required to include rather than including them manually?

Thanks :)
Flags: needinfo?(wmccloskey)
Hi Henry,
I would rather do this differently. Right now we generate a constructor function for each IPC message type. You can see some examples here:
https://searchfox.org/mozilla-central/source/__GENERATED__/ipc/ipdl/PContent.cpp#49

I think the right way to do this is to change the code in lower.py that generates these constructors so that it passes in the standard segment capacity to the Message constructor. The Python code to generate the constructors is here:
http://searchfox.org/mozilla-central/rev/1b7b1ec949497e9fc2a9b9dfaccbe894ee2ad5ef/ipc/ipdl/ipdl/lower.py#1695-1736

This code gets called from here:
http://searchfox.org/mozilla-central/rev/1b7b1ec949497e9fc2a9b9dfaccbe894ee2ad5ef/ipc/ipdl/ipdl/lower.py#1580-1596
I think this is the place you'll need to modify. You should be able to look up the message in a dictionary that's from from the .ini file to get the default size. Then you can pass it in as an argument.
Flags: needinfo?(wmccloskey)
Comment hidden (mozreview-request)
Assignee

Comment 29

2 years ago
Hi Bill,

I believe I have followed your instruction in comment 27 to have
a new patch pushed to reviewboard. What I am only uncertain is
where/how to use the default segment size (which is 4096.)
My current setup is to use '0' as an indicator to use the 
default segment size so we don't have to specify the actual
default segment size in the codegen level. Instead, we define
the default segment size in ipc_message.cc.

Besides, regarding the ini file, I name it to message-metadata.ini
so that we can put any kind of metadata in it in the future
when needed. Do you think if it's a good idea?

Thanks :)
Flags: needinfo?(wmccloskey)
Comment hidden (mozreview-request)
Assignee

Comment 31

2 years ago
I submitted version 4 for:

1) More custom segment capacities based on 

https://docs.google.com/spreadsheets/d/1qYpO4vBL2cPHWvHLZhjtAJR_HRGKeQNYSVmgzRUO9PE/edit#gid=1353915496

2) Added typo-proof check in ipdl.py. It works by enumerating all [protocol_name:message_name] from
   all ipdl files and compare if message-metadata.ini contains any message not in the enumerated
   ones.

3) Use default segment capacity for all "reply" messages. The ini file doesn't specify
   the capacity is for send or reply. In version 3, both way would use the same capacity.
   However, considering the reply message is usually very trivial and we are removing
   sync messages, using default capacity for serializing reply messages should be fine :)
Assignee

Updated

2 years ago
Attachment #8879882 - Flags: review?(wmccloskey)
Comment on attachment 8879882 [details]
Bug 1348591 - Support custom default segment buffer list size.

https://reviewboard.mozilla.org/r/151288/#review157556

::: ipc/chromium/src/base/pickle.cc:130
(Diff revision 2)
>  }
>  
>  // Payload is sizeof(Pickle::memberAlignmentType) aligned.
>  
> -Pickle::Pickle(uint32_t header_size)
> -    : buffers_(AlignInt(header_size), kHeaderSegmentCapacity, kDefaultSegmentCapacity),
> +Pickle::Pickle(uint32_t header_size, size_t default_segment_capacity)
> +    : buffers_(AlignInt(header_size), kHeaderSegmentCapacity, default_segment_capacity),

I think it would be better to use the default_segment_capacity for the second argument here as well (initial capacity). I don't see any reason to make the first segment be small if we expect these messages to be large. We only want to do this if we have a default_segment_capacity, though.

::: ipc/chromium/src/chrome/common/ipc_message.cc:23
(Diff revision 2)
> +#include "mozilla/dom/PContent.h"
> +#include "mozilla/layers/PLayerTransaction.h"

????

::: ipc/chromium/src/chrome/common/ipc_message.cc:49
(Diff revision 2)
> +    size_t mSize;
> +  } kMessageSizeTable[] = {
> +#include "IPCMessageSize.inc"
> +  };
> +
> +  for (size_t i = 0; i < mozilla::ArrayLength(kMessageSizeTable); i++) {

The .inc file should be sorted so that we can use binary search here.

::: ipc/chromium/src/base/pickle.cc:130
(Diff revision 4)
>  }
>  
>  // Payload is sizeof(Pickle::memberAlignmentType) aligned.
>  
> -Pickle::Pickle(uint32_t header_size)
> -    : buffers_(AlignInt(header_size), kHeaderSegmentCapacity, kDefaultSegmentCapacity),
> +Pickle::Pickle(uint32_t header_size, size_t segment_capacity)
> +    : buffers_(AlignInt(header_size), kHeaderSegmentCapacity, segment_capacity),

If segment_capacity is not the default segment capacity, I think we should use it for the first segment as well (instead of kHeaderSegmentCapacity).

It probably makes sense to pass 0 for segment_capacity if we want the default. We would continue to define kDefaultSegmentCapacity in Pickle. Then the constructor would look like:

buffers_(AlignInt(header_size),
         segment_capacity ? segment_capacity : kHeaderSegmentCapacity,
         segment_capacity ? segment_capacity : kDefaultSegmentCapacity)
         
Also, you could make the default value of segment_capacity be 0.

::: ipc/chromium/src/chrome/common/ipc_message.cc:32
(Diff revision 4)
>  #define MSG_HEADER_SZ sizeof(Header)
>  #endif
>  
>  namespace IPC {
>  
> +static const uint32_t kDefaultSegmentCapacity = 4096;

This could then be removed.

::: ipc/chromium/src/chrome/common/ipc_message.cc:41
(Diff revision 4)
>  Message::~Message() {
>    MOZ_COUNT_DTOR(IPC::Message);
>  }
>  
>  Message::Message()
> -    : Pickle(MSG_HEADER_SZ) {
> +    : Pickle(MSG_HEADER_SZ, kDefaultSegmentCapacity) {

This wouldn't need to change.

::: ipc/chromium/src/chrome/common/ipc_message.cc:60
(Diff revision 4)
>  #endif
>    InitLoggingVariables();
>  }
>  
> -Message::Message(int32_t routing_id, msgid_t type, NestedLevel nestedLevel, PriorityValue priority,
> +Message::Message(int32_t routing_id, msgid_t type,
> +                 uint32_t segmentCapacity, 

You have an extra space at the end of the line. Also, please call this segment_capacity.

::: ipc/chromium/src/chrome/common/ipc_message.cc:63
(Diff revision 4)
>  
> -Message::Message(int32_t routing_id, msgid_t type, NestedLevel nestedLevel, PriorityValue priority,
> +Message::Message(int32_t routing_id, msgid_t type,
> +                 uint32_t segmentCapacity, 
> +                 NestedLevel nestedLevel, PriorityValue priority,
>                   MessageCompression compression, const char* const aName, bool recordWriteLatency)
> -    : Pickle(MSG_HEADER_SZ) {
> +    : Pickle(MSG_HEADER_SZ, segmentCapacity ? segmentCapacity : kDefaultSegmentCapacity) {

You won't need the conditional here. Just pass segment_capacity.

::: ipc/ipdl/ipdl.py:184
(Diff revision 4)
> -    ipdl.gencxx(filename, ast, headersdir, cppdir)
> +    ipdl.gencxx(filename, ast, headersdir, cppdir, segmentCapacityDict)
>  
>      if ast.protocol:
>          allmessages[ast.protocol.name] = ipdl.genmsgenum(ast)
>          allprotocols.append('%sMsgStart' % ast.protocol.name)
> +        # e.g. PContent::RequestMemoryReport (not prefixed or sufficed.)

suffixed
Attachment #8879882 - Flags: review?(wmccloskey)
Sorry, MozReview mixed up my comments from the old version of the patch and the new one.

The new patch looks good. I've just requested a few changes to the argument handling.
Flags: needinfo?(wmccloskey)
Comment hidden (mozreview-request)
Comment hidden (mozreview-request)
Assignee

Comment 36

2 years ago
Hi Bill,

I have a new patch submitted (which addressed all your comments) so could you help
review again? Thanks :)
Comment on attachment 8879882 [details]
Bug 1348591 - Support custom default segment buffer list size.

https://reviewboard.mozilla.org/r/151288/#review159664

::: ipc/chromium/src/chrome/common/ipc_message.h:70
(Diff revision 6)
>    //
>    // NOTE: `recordWriteLatency` is only passed by IPDL generated message code,
>    // and is used to trigger the IPC_WRITE_LATENCY_MS telemetry.
>    Message(int32_t routing_id,
>            msgid_t type,
> +          uint32_t segmentCapacity = 0, // 0 for the default capacity.

You'll need to fix this constructor here:
http://searchfox.org/mozilla-central/rev/e8f4f51cd543f203e9cb861cecb7545ac43c836c/ipc/glue/ProtocolUtils.cpp#77

Or you can delete it since it's unused (as well as the Open and Bridge functions).

::: ipc/chromium/src/chrome/common/ipc_message.cc:57
(Diff revision 6)
> -Message::Message(int32_t routing_id, msgid_t type, NestedLevel nestedLevel, PriorityValue priority,
> +Message::Message(int32_t routing_id, msgid_t type,
> +                 uint32_t segment_capacity,
> +                 NestedLevel nestedLevel, PriorityValue priority,
>                   MessageCompression compression, const char* const aName, bool recordWriteLatency)

Please put each argument on its own line.
Attachment #8879882 - Flags: review?(wmccloskey) → review+
Assignee

Comment 38

2 years ago
Thanks Bill!

(In reply to Bill McCloskey (:billm) from comment #37)
> Comment on attachment 8879882 [details]
> Bug 1348591 - Support custom default segment buffer list size.
> 
> https://reviewboard.mozilla.org/r/151288/#review159664
> 
> ::: ipc/chromium/src/chrome/common/ipc_message.h:70
> (Diff revision 6)
> >    //
> >    // NOTE: `recordWriteLatency` is only passed by IPDL generated message code,
> >    // and is used to trigger the IPC_WRITE_LATENCY_MS telemetry.
> >    Message(int32_t routing_id,
> >            msgid_t type,
> > +          uint32_t segmentCapacity = 0, // 0 for the default capacity.
> 
> You'll need to fix this constructor here:
> http://searchfox.org/mozilla-central/rev/
> e8f4f51cd543f203e9cb861cecb7545ac43c836c/ipc/glue/ProtocolUtils.cpp#77
> 
> Or you can delete it since it's unused (as well as the Open and Bridge
> functions).
> 

This is so scary! I fixed the similar issue in Shmem.cpp but still missed
this one. I'd like to move the newly added argument (segment_capacity) 
all the way to be the last one to avoid this kind of mismatch. 
Do you have any concern on this change?

Thank!
Flags: needinfo?(wmccloskey)
I don't really care about the order. However, you can find all the calls to that particular Message constructor with this search:

http://searchfox.org/mozilla-central/search?q=symbol:_ZN3IPC7MessageC1EijNS0_11NestedLevelENS0_13PriorityValueENS0_18MessageCompressionEPKcb&redirect=false

Aside from generated code, there aren't very many, and it's easy to see that you'll have covered them all once the ChannelOpened thing is fixed.
Flags: needinfo?(wmccloskey)
Comment hidden (mozreview-request)
Comment hidden (mozreview-request)

Comment 42

2 years ago
Pushed by hchang@mozilla.com:
https://hg.mozilla.org/integration/autoland/rev/e3a6a933eee5
Support custom default segment buffer list size. r=billm

Comment 43

2 years ago
bugherder
https://hg.mozilla.org/mozilla-central/rev/e3a6a933eee5
Status: NEW → RESOLVED
Last Resolved: 2 years ago
Resolution: --- → FIXED
Target Milestone: --- → mozilla56
See Also: → 1380974
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