Summary:
When compression is enabled, and blocksize is not too big, use the
space in stack to hold bytes read from block.
Bencmark:
base version: commit 8f09d53fd11a7debe1e48b73a192de3a458d37bf
malloc: 1.30% -> 0.98%
free: 1.49% -> 1.07%
Test Plan:
make all check
Reviewers: ljin, yhchiang, dhruba, igor, sdong
Reviewed By: sdong
Subscribers: leveldb
Differential Revision: https://reviews.facebook.net/D20679
b0999011e2