1249174 - Shrink XPT info some more

Status: RESOLVED FIXED

(Core :: XPCOM, defect)

Description

[Nicholas Nethercote [inactive]]

I have a couple of patches that shrink the size of the XPT info a bit.

Comment 1

[Nicholas Nethercote [inactive]]

Attachment: (part 1) - Don't store the unused XPTTypeDescriptorTags::argnum2 field in memory

PTTypeDescriptor::argnum2 is unused. Removing it reduces
sizeof(XPTTypeDescriptor) from 6 bytes to 4 bytes, which reduces the
"xpti-working-set" measurement by 80 KiB (measured on 64-bit).

Comment 2

[Nicholas Nethercote [inactive]]

Attachment: (part 2) - Shrink xptiInterfaceEntry by reordering its fields

This reduces "xpti-working-set" by another 16 KiB on 64-bit.

Comment 3

[Nicholas Nethercote [inactive]]

Attachment: (part 3) - Don't store the unused XPTInterfaceDirectoryEntry::name_space field in memory

Removing it reduces the "xpti-working-set" measurement by 16 KiB (measured on
64-bit).

Comment 4

[Nicholas Nethercote [inactive]]

Attachment: (part 4) - Don't store unused XPTHeader fields in memory

This requires merging XPT_DoHeaderPrologue() and XPT_DoHeader(), which is
straightforward.

This reduces "xpti-working-set" by 16 KiB on 64-bit platforms.

Comment 5

[Nicholas Nethercote [inactive]]

Attachment: (part 5) - Remove the useless BLK_HDR::size field

Comment 6

[Nicholas Nethercote [inactive]]

Attachment: (part 6) - Shrink XPTTypeDescriptor

With careful layout we can reduce sizeof(XPTTypeDescriptor) from 4 to 3, which
also reduces sizeof(XPTParamDescriptor) from 6 to 4. This reduces
"xpti-working-set" by 16 KiB.

The union-of-structs also improves readability by making it clearer exactly
which fields are used for which types.

Comment 7

[Nicholas Nethercote [inactive]]

Attachment: (part 7) - Avoid wasted space around XPT strings

This patch:

- Removes XPTArena's ability to support any alignment.

- Hardwires two sub-arenas into XPTArena, one with alignment of 8 and one with
  alignment of 1.

- Uses the first sub-arena for most allocations and the second sub-arena for C
  string allocations.

These changes reduce "xpti-working-set" by 56 KiB.

The patch also removes the XPT_MALLOC macro in favour of an XPT_CALLOC one, to
make clearer that the result is always zeroed.

Comment 8

[Nicholas Nethercote [inactive]]

Attachment: (part 7) - Avoid wasted space around XPT strings

(A tweaked version of the previous patch.)

Comment 9

[Nicholas Nethercote [inactive]]

Attachment: (part 8) - Shrink XPTInterfaceDescriptor

PTInterfaceDescriptor::num_additional_types can easily fit in 8 bits -- in
practice it doesn't exceed 20, and there's already a check in DoTypeDescriptor
that it doesn't exceed 255. This patch shrinks it and moves that check into
XPT_InterfaceDescriptorAddTypes() so that any overflow would be detected more
reliably.

On 64-bit platforms this reduces sizeof(XPTInterfaceDescriptor) from 40 to 32
and correspondingly reduces "xpti-working-set" by 16 KiB.

The patch also changes XPT_InterfaceDescriptorAddTypes() into a local function,
because it's defined and only used in xpt_struct.cpp.

Comment 10

[Nicholas Nethercote [inactive]]

The eight patches reduce "xpti-working-set" (on 64-bit platforms) from 1184 KiB to 968 KiB -- a reduction of 216 KiB -- and I'm out of ideas for now.

Comment 11

[Nicholas Nethercote [inactive]]

Attachment: (part 4) - Don't store unused XPTHeader fields in memory

(I tweaked a comment.)

Comment 12

[Nicholas Nethercote [inactive]]

Attachment: (part 8) - Shrink XPTInterfaceDescriptor

(I tweaked a comment.)

Comment 13

[Nicholas Nethercote [inactive]]

(In reply to Nicholas Nethercote [:njn] from comment #10)
> The eight patches reduce "xpti-working-set" (on 64-bit platforms) from 1184
> KiB to 968 KiB -- a reduction of 216 KiB -- and I'm out of ideas for now.

I measured on 32-bit as well: 936 KiB drops to 776 KiB, a 160 KiB reduction.

Comment 14

[Nicholas Nethercote [inactive]]

https://hg.mozilla.org/integration/mozilla-inbound/rev/fa81f18d5093d47064913e1e7fb6c54d03419df0
Bug 1249174 (part 7) - Only define XPTArena::name if XPT_ARENA_LOGGING is defined. r=khuey.

Comment 15

[Nicholas Nethercote [inactive]]

(In reply to Nicholas Nethercote [:njn] from comment #14)
> https://hg.mozilla.org/integration/mozilla-inbound/rev/
> fa81f18d5093d47064913e1e7fb6c54d03419df0
> Bug 1249174 (part 7) - Only define XPTArena::name if XPT_ARENA_LOGGING is
> defined. r=khuey.

Whoops. That was meant to be part of bug 1248534, which blocks this one, but I got the bug number wrong. No matter, I'll rename the part 7 above ("Avoid wasted space around XPT strings") to 7.5 to avoid further confusion.

Comment 16

[Carsten Book [:Tomcat]]

https://hg.mozilla.org/mozilla-central/rev/fa81f18d5093

Comment 17

[Nicholas Nethercote [inactive]]

More patches to land here.

Comment 18

[Nicholas Nethercote [inactive]]

https://hg.mozilla.org/integration/mozilla-inbound/rev/639ee2cb781c339fe86fd1fed4122b809d2a1fc1
Bug 1249174 (part 1) - Don't store the unused XPTTypeDescriptorTags::argnum2 field in memory. r=khuey.

https://hg.mozilla.org/integration/mozilla-inbound/rev/d8db031fc4a77c85088755f1919d9c4e11b82fed
Bug 1249174 (part 2) - Shrink xptiInterfaceEntry by reordering its fields. r=khuey.

https://hg.mozilla.org/integration/mozilla-inbound/rev/df54281b08634341fb1a421b9753718966c45fe7
Bug 1249174 (part 3) - Don't store the unused XPTInterfaceDirectoryEntry::name_space field in memory. r=khuey.

https://hg.mozilla.org/integration/mozilla-inbound/rev/f4296d24c1f357f6b45acd50e76ea056afe3e2cc
Bug 1249174 (part 4) - Don't store unused XPTHeader fields in memory. r=khuey.

https://hg.mozilla.org/integration/mozilla-inbound/rev/69bc807d8b8a36604f313626071fa4d624e8605d
Bug 1249174 (part 5) - Remove the useless BLK_HDR::size field. r=khuey.

https://hg.mozilla.org/integration/mozilla-inbound/rev/6a5f30460690b5089f648e8a38eed27d52a8d597
Bug 1249174 (part 6) - Shrink XPTTypeDescriptor. r=khuey.

https://hg.mozilla.org/integration/mozilla-inbound/rev/ca3090cb8e36dd77612ffdc84cd8953897ff72fd
Bug 1249174 (part 7.5) - Avoid wasted space around XPT strings. r=khuey.

https://hg.mozilla.org/integration/mozilla-inbound/rev/b5d5f42ed917c073f2edaeb01e97f88bdaa4d1fd
Bug 1249174 (part 8) - Shrink XPTInterfaceDescriptor. r=khuey.

Comment 19

[Carsten Book [:Tomcat]]

https://hg.mozilla.org/mozilla-central/rev/639ee2cb781c
https://hg.mozilla.org/mozilla-central/rev/d8db031fc4a7
https://hg.mozilla.org/mozilla-central/rev/df54281b0863
https://hg.mozilla.org/mozilla-central/rev/f4296d24c1f3
https://hg.mozilla.org/mozilla-central/rev/69bc807d8b8a
https://hg.mozilla.org/mozilla-central/rev/6a5f30460690
https://hg.mozilla.org/mozilla-central/rev/ca3090cb8e36
https://hg.mozilla.org/mozilla-central/rev/b5d5f42ed917