Use hash func to boost file creation and lookup

[RoyWFHuang]

Previously, SimpleFS used a sequential insertion method to create files, which worked efficiently when the filesystem contained only a small number of files.
However, in real-world use cases, filesystems often manage a large number of files, making sequential search and insertion inefficient.
Inspired by Ext4’s hash-based directory indexing, this change adopts a hash function to accelerate file indexing and improve scalability.

Change:
Implemented hash-based file index lookup
Improved scalability for large directory structures

hash_code = file_hash(file_name);

extent index = hash_code / SIMPLEFS_MAX_BLOCKS_PER_EXTENT
block index = hash_code % SIMPLEFS_MAX_BLOCKS_PER_EXTENT;

 inode
  +-----------------------+
  | i_mode = IFDIR | 0755 |      block 123 (simplefs_file_ei_block)
  | ei_block = 123    ----|--->  +----------------+
  | i_size = 4 KiB        |      | nr_files  = 7  |
  | i_blocks = 1          |      |----------------|
  +-----------------------+    0 | ee_block  = 0  |
              (extent index = 0) | ee_len    = 8  |
                                 | ee_start  = 84 |--->  +-------------+ block 84(simplefs_dir_block)
                                 | nr_file   = 2  |      |nr_files = 2 | (block index = 0)
                                 |----------------|      |-------------|
                               1 | ee_block  = 8  |    0 | inode  = 24 |
              (extent index = 1) | ee_len    = 8  |      | nr_blk = 1  |
                                 | ee_start  = 16 |      | (foo)       |
                                 | nr_file   = 5  |      |-------------|
                                 |----------------|    1 | inode  = 45 |
                                 | ...            |      | nr_blk = 14 |
                                 |----------------|      | (bar)       |
                             341 | ee_block  = 0  |      |-------------|
            (extent index = 341) | ee_len    = 0  |      | ...         |
                                 | ee_start  = 0  |      |-------------|
                                 | nr_file   = 12 |   14 | 0           |
                                 +----------------+      +-------------+ block 85(simplefs_dir_block)
                                                         |nr_files = 2 | (block index = 1)
                                                         |-------------|
                                                       0 | inode  = 48 |
                                                         | nr_blk = 15 |
                                                         | (foo1)      |
                                                         |-------------|
                                                       1 | inode  = 0  |
                                                         | nr_blk = 0  |
                                                         |             |
                                                         |-------------|
                                                         | ...         |
                                                         |-------------|
                                                      14 | 0           |
                                                         +-------------+

Performance test

• Random create 30600 files into filesystem

legacy:

         168140.12 msec task-clock                       #    0.647 CPUs utilized
            111367      context-switches                 #  662.346 /sec
             40917      cpu-migrations                   #  243.351 /sec
           3736053      page-faults                      #   22.220 K/sec
      369091680702      cycles                           #    2.195 GHz
      168751830643      instructions                     #    0.46  insn per cycle
       34044524391      branches                         #  202.477 M/sec
         768151711      branch-misses                    #    2.26% of all branches

     259.842753513 seconds time elapsed
      23.000247000 seconds user
     150.380145000 seconds sys

full_name_hash

         167926.13 msec task-clock                       #    0.755 CPUs utilized
            110631      context-switches                 #  658.808 /sec
             43835      cpu-migrations                   #  261.037 /sec
           3858617      page-faults                      #   22.978 K/sec
      392878398961      cycles                           #    2.340 GHz
      207287412692      instructions                     #    0.53  insn per cycle
       42556269864      branches                         #  253.423 M/sec
         840868990      branch-misses                    #    1.98% of all branches

     222.274028604 seconds time elapsed
      20.794966000 seconds user
     151.941876000 seconds sys

---

• Random remove 30600 files into filesystem

legacy:

         104332.44 msec task-clock                       #    0.976 CPUs utilized
             56514      context-switches                 #  541.672 /sec
              1174      cpu-migrations                   #   11.252 /sec
           3796962      page-faults                      #   36.393 K/sec
      258293481279      cycles                           #    2.476 GHz
      153853176926      instructions                     #    0.60  insn per cycle
       30434271757      branches                         #  291.705 M/sec
         532967347      branch-misses                    #    1.75% of all branches

     106.921706288 seconds time elapsed
      16.987883000 seconds user
      91.268661000 seconds sys

full_name_hash

          83278.61 msec task-clock                       #    0.967 CPUs utilized
             52431      context-switches                 #  629.585 /sec
              1309      cpu-migrations                   #   15.718 /sec
           3796501      page-faults                      #   45.588 K/sec
      199894058328      cycles                           #    2.400 GHz
      110625460371      instructions                     #    0.55  insn per cycle
       20325767251      branches                         #  244.069 M/sec
         490549944      branch-misses                    #    2.41% of all branches

      86.132655220 seconds time elapsed
      19.180209000 seconds user
      68.476075000 seconds sys

• Random check (ls -la filename) 30600 files into filesystem
  Use perf stat ls -la to measure the query time for each file and sum up all elapsed times to calculate the total lookup cost.

Legacy :
min time: 0.00171 s
max time: 0.03799 s
avg time: 0.00423332 s
tot time: 129.539510 s

full_name_hash:
min time: 0.00171 s
max time: 0.03588 s
avg time: 0.00305601 s
tot time: 93.514040 s

---

Summary by cubic

Switched SimpleFS to configurable hash-based directory indexing (FNV‑1a in tests) to speed up file creation and lookup by mapping filenames to extent/block slots. On 30.6k files: create ~33% faster, delete ~12% faster, lookup ~41% faster.

• New Features

  • Kconfig-selectable hash (hash64, FNV‑1a, full_name_hash); hash-guided placement/lookup in create, link, symlink, rename, and unlink.
  • Added fast __file_lookup and early-stop iteration using per-extent counts; reclaims empty extents on unlink/rename.

• Refactors

  • Moved symlink inode ops to symlink.c and updated build to include symlink.o and hash.o.
  • Replaced printk with pr_* for logging.

^{Written for commit c2316df. Summary will update automatically on new commits.}

[jserv]

How can you determine which hash function is the most suitable?

[cubic-dev-ai]

1 issue found across 8 files

Prompt for AI agents (all 1 issues)

Understand the root cause of the following 1 issues and fix them.


<file name="simplefs.h">

<violation number="1" location="simplefs.h:122">
Declaring `simplefs_file_vm_ops` as `static` in the header defines a zeroed vm_ops instance in every translation unit instead of referencing a single populated table. Please make this an extern declaration so consumers can use the real ops struct.</violation>
</file>

---

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[visitorckw]

I saw that your PR description includes some performance benchmarks, but the commit message lacks any performance numbers to support your improvements. Please improve the commit message.

[RoyWFHuang]

How can you determine which hash function is the most suitable?

I’m not sure if "fnv" is the most suitable, but index in SimpleFS is relatively small, using a more complex algorithm might not provide significant benefits. I think fnv is a reasonable balance between simplicity and performance.

[visitorckw]

You ignored many of my comments without making any changes or providing any replies. You still retained many irrelevant changes, making the review difficult. Additionally, a single-line commit message saying only "optimize the file search process" is way too vague. Please improve the git commit message.

[RoyWFHuang]

I saw that your PR description includes some performance benchmarks, but the commit message lacks any performance numbers to support your improvements. Please improve the commit message.

Added all hash results into the commit.