Remove reallocation of AlignedBuffer in direct_io sync reads if already aligned (#11600)
Summary:
Remove reallocation of AlignedBuffer in direct_io sync reads in RandomAccessFileReader::Read if buffer passed is already aligned.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/11600
Test Plan:
Setup: `TEST_TMPDIR=./tmp-db/ ./db_bench -benchmarks=filluniquerandom -disable_auto_compactions=true -target_file_size_base=1048576 -write_buffer_size=1048576 -compression_type=none`
Benchmark: `TEST_TMPDIR=./tmp-db/ perf record ./db_bench --cache_size=8388608 --use_existing_db=true --disable_auto_compactions=true --benchmarks=seekrandom --use_direct_reads=true -use_direct_io_for_flush_and_compaction=true -reads=1000 -seek_nexts=1 -max_auto_readahead_size=131072 -initial_auto_readahead_size=16384 -adaptive_readahead=true -num_file_reads_for_auto_readahead=0`
Perf profile-
Before:
```
8.73% db_bench libc.so.6 [.] __memmove_evex_unaligned_erms
3.34% db_bench [kernel.vmlinux] [k] filemap_get_read_batch
```
After:
```
2.50% db_bench [kernel.vmlinux] [k] filemap_get_read_batch
2.29% db_bench libc.so.6 [.] __memmove_evex_unaligned_erms
```
`make crash_test -j `with direct_io enabled completed succesfully locally.
Ran few benchmarks with direct_io from seek_nexts varying between 912 to 327680 and different readahead_size parameters and it showed no regression so far.
Reviewed By: ajkr
Differential Revision: D47478598
Pulled By: akankshamahajan15
fbshipit-source-id: 6a48e21cb34696f5d09c22a6311a3a1cb5f9cf33
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akankshamahajan