[v23.3.x] cloud_storage: concurrent directory walking #19816
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(cherry picked from commit ec6b770)
This makes it possible to walk directories concurrently. It will be done in a subsequent commit. (cherry picked from commit ec0e855)
(cherry picked from commit 1c7d481)
One step closer to concurrent walking. (cherry picked from commit f856d46)
This speeds up cache trimming by 2 orders of magnitude even on a lightly
loaded reactor. At the cost of higher number of open fds (up to 2K
increase: one for directory, one for the stat call in
`walk_accumulator::visit`). Also, higher pressure on the reactor (extra
1K futures/tasks), IO subsystem, syscall thread.
"Lightly loaded reactor" test case:
```cpp
SEASTAR_THREAD_TEST_CASE(empty_dir) {
cloud_storage::recursive_directory_walker w;
const std::filesystem::path target_dir = "/tmp/recdirtest";
stress_config cfg;
cfg.min_spins_per_scheduling_point = 1;
cfg.max_spins_per_scheduling_point = 1;
cfg.num_fibers = 1;
auto mgr = stress_fiber_manager{};
BOOST_REQUIRE(mgr.start(cfg));
access_time_tracker tracker;
auto result = w.walk(target_dir.native(), tracker).get();
mgr.stop().get();
}
```
/tmp/recdirtest is filled by the following script:
```py
import os
import xxhash
from pathlib import Path
for folders in range (0, 600000):
x = xxhash.xxh32()
x.update(f'folder{folders}')
d = x.hexdigest();
Path(f"./{d}/kafka").mkdir(parents=True, exist_ok=True)
open(f'./{d}/kafka/segment.bin', 'a').close()
```
(cherry picked from commit ee34998)
(cherry picked from commit 5d48458)
(cherry picked from commit 8ad8459)
(cherry picked from commit 3fedeb3)
andrwng
approved these changes
Jun 13, 2024
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Backport of PR #18758