tree 718394b40b40b76718b22f2f66ed1ae1853926a7
parent 5d7efef2982b8a84755e0d1d96cb611d06652136
author Primiano Tucci <primiano@google.com> 1698181086 +0100
committer Android Build Coastguard Worker <android-build-coastguard-worker@google.com> 1709043611 +0000

traced: make CloneReadOnly() copy only used portion of the buffer

Before this change CloneReadOnly() would memcpy the whole buffer
when cloning. This has two side-effects:
1. Causes a read-only page-fault on the original buffer. This is
   typically not a huge deal because both Linux and Window will
   map all that memory to the zero-page until a RW fault happens.
2. The cloned buffer will be filled with zeros up to the declared
   size. This can cause memory spikes.

The memory spikes wouldn't be a huge deal normally, because we
expect the buffer to be eventually fully used.
However, recently we introduced edge use cases where we declare
extremely large (~500MB) buffers and expect to use them only in
the case of a bugreport (But not fully). In this case the memory
spike is undesirable.

Bug: 307542353
Bug: 296227911
Test: perfetto_unittests --gtest_filter=TraceBufferTest.*
(cherry picked from commit 88060ce0324ec8dec6a1f9a9084033b4b7049a29)
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:133f99fc7a967313509db6ddbb9c86400f5c18a0)
Merged-In: Ie53ee2b854cf2da488d115623dbdcf959fbacade
Change-Id: Ie53ee2b854cf2da488d115623dbdcf959fbacade