Use a GHashTable to store cpr fds to reduce the time
consumption of `cpr_find_fd` in scenarios with a large
number of fds. The time complexity for `cpr_find_fd` is
reduced from O(N) to O(1).
Keep cpr fds lookups in a GHashTable during normal runtime
while preserving the existing QLIST migration ABI. Build a
temporary QLIST from the hash table in pre_save and rebuild
the hash table from the loaded QLIST in post_load.
To demonstrate the performance improvement, we tested the total time
consumed by `cpr_find_fd` (called N times for N fds) under our real-world
business scenarios with different numbers of file descriptors. The results
are measured in nanoseconds:
| Number of FDs | Total time with QLIST (ns) | Total time with GHashTable (ns) |
|---------------|----------------------------|---------------------------------|
| 540 | 936,753 | 393,358 |
| 2,870 | 24,102,342 | 2,212,113 |
| 7,530 | 152,715,916 | 5,474,310 |
As shown in the data, the lookup time grows exponentially with the QLIST
as the number of fds increases. With the GHashTable, the time consumption
remains linear (O(1) per lookup), significantly reducing the downtime during
the CPR process.
Signed-off-by: hongmianquan <hongmianquan@bytedance.com>
Link: https://lore.kernel.org/r/20260519134315.27997-1-hongmianquan@bytedance.com
Signed-off-by: Peter Xu <peterx@redhat.com>
a181df93bb