commit cd15ca3178ec45ef6cc27453326004d102c8dc4c
author Aaron Green <aarongreen@google.com> Tue May 21 22:50:09 2024 +0000
committer CQ Bot Account <pigweed-scoped@luci-project-accounts.iam.gserviceaccount.com> Tue May 21 22:50:09 2024 +0000
tree b2d9a58eaa6ef55d0a1b0d37b233ecb7bf5d34e7
parent cae40e3337b2234b2618cd506ecbb089c25a4e40

pw_allocator: Track requested sizes in blocks

Previously, TrackingAllocator allocated extra space to store the
requested layout when it was requested to be tracked. This allowed it to
work with any allocator, but prevented the allocators it wrapped from
being able to make any adjustments to allocations, e.g. for
fragmentation purposes.

Moreover, all the usages of Block designed to address more than 64K of
memory are already wasting 2 bytes, since the offset type would be at
least 4 bytes, and the "info" field only 2.

Finally, the difference between the requested and allocated sizes are
guaranteed to be less than a block overhead, which is much less than
64K.

As a result, this CL:
 * Stores the excess bytes in a uint16_t "padding" field.
 * Implements GetRequestLayout for block allocators using that padding.
 * Simplifies TrackingAllocator by only support request_bytes metrics
   for allocators that implement GetRequestLayout.

Change-Id: I0303667afeadf90a8f44cd8866fb1adbf8f8b6d6
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/210395
Reviewed-by: Taylor Cramer <cramertj@google.com>
Lint: Lint 🤖 <android-build-ayeaye@system.gserviceaccount.com>
Reviewed-by: Keir Mierle <keir@google.com>
Commit-Queue: Aaron Green <aarongreen@google.com>