Remove reallocation of AlignedBuffer in direct_io sync reads if already aligned

[akankshamahajan15]

Summary: Remove reallocation of AlignedBuffer in direct_io sync reads in RandomAccessFileReader::Read if buffer passed is already aligned.

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.

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[ajkr]

LGTM. I think #11602 can be finished later, or never if it's not correct or not cleaner

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@akankshamahajan15 merged this pull request in 749b179.