tree 79ee13e088f9b300186d0fd098d908888f04fc57
parent 0d7e8800c9ad599ca33e7f53009db5c8e18f33c5
author Snehasish Kumar <snehasishk@google.com> 1633989809 -0700
committer Copybara-Service <copybara-worker@google.com> 1636659383 -0800

[memprof] Replace the block cache with a hashmap.

The existing implementation uses a cache + eviction based scheme to
record heap profile information. This design was adopted to ensure a
constant memory overhead (due to fixed number of cache entries) along
with incremental write-to-disk for evictions. We find that since the
number to entries to track is O(unique-allocation-contexts) the overhead
of keeping all contexts in memory is not very high. On a clang workload,
the max number of unique allocation contexts was ~35K, median ~11K.
For each context, we (currently) store 64 bytes of data - this amounts
to 5.5MB (max). Given the low overheads for a complex workload, we can
simplify the implementation by using a hashmap without eviction.

Other changes:
* Memory map is dumped at the end rather than startup. The relative
order in the profile dump is unchanged since we no longer have evicted
entries at runtime.
* Added a test to check meminfoblocks are merged.

Differential Revision: https://reviews.llvm.org/D111676

GitOrigin-RevId: 1243cef245f6131c093d65235e87319e8e124e7f