hugetlb: code clean for hugetlb_hstate_alloc_pages

Patch series "hugetlb: parallelize hugetlb page init on boot", v6.

Introduction
------------
Hugetlb initialization during boot takes up a considerable amount of time.
For instance, on a 2TB system, initializing 1,800 1GB huge pages takes
1-2 seconds out of 10 seconds.  Initializing 11,776 1GB pages on a 12TB
Intel host takes more than 1 minute[1].  This is a noteworthy figure.

Inspired by [2] and [3], hugetlb initialization can also be accelerated
through parallelization.  Kernel already has infrastructure like
padata_do_multithreaded, this patch uses it to achieve effective results
by minimal modifications.

[1] https://lore.kernel.org/all/[email protected]/
[2] https://lore.kernel.org/all/[email protected]/
[3] https://lore.kernel.org/all/[email protected]/
[4] https://lore.kernel.org/all/[email protected]/

max_threads
-----------
This patch use `padata_do_multithreaded` like this:

```
job.max_threads	= num_node_state(N_MEMORY) * multiplier;
padata_do_multithreaded(&job);
```

To fully utilize the CPU, the number of parallel threads needs to be
carefully considered.  `max_threads = num_node_state(N_MEMORY)` does not
fully utilize the CPU, so we need to multiply it by a multiplier.

Tests below indicate that a multiplier of 2 significantly improves
performance, and although larger values also provide improvements, the
gains are marginal.

  multiplier     1       2       3       4       5
 ------------ ------- ------- ------- ------- -------
  256G 2node   358ms   215ms   157ms   134ms   126ms
  2T   4node   979ms   679ms   543ms   489ms   481ms
  50G  2node   71ms    44ms    37ms    30ms    31ms

Therefore, choosing 2 as the multiplier strikes a good balance between
enhancing parallel processing capabilities and maintaining efficient
resource management.

Test result
-----------
      test case       no patch(ms)   patched(ms)   saved
 ------------------- -------------- ------------- --------
  256c2T(4 node) 1G           4745          2024   57.34%
  128c1T(2 node) 1G           3358          1712   49.02%
     12T         1G          77000         18300   76.23%

  256c2T(4 node) 2M           3336          1051   68.52%
  128c1T(2 node) 2M           1943           716   63.15%


This patch (of 8):

The readability of `hugetlb_hstate_alloc_pages` is poor.  By cleaning the
code, its readability can be improved, facilitating future modifications.

This patch extracts two functions to reduce the complexity of
`hugetlb_hstate_alloc_pages` and has no functional changes.

- hugetlb_hstate_alloc_pages_node_specific() to handle iterates through
  each online node and performs allocation if necessary.
- hugetlb_hstate_alloc_pages_report() report error during allocation.
  And the value of h->max_huge_pages is updated accordingly.

Link: https://lkml.kernel.org/r/[email protected]
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Gang Li <[email protected]>
Tested-by: David Rientjes <[email protected]>
Reviewed-by: Muchun Song <[email protected]>
Reviewed-by: Tim Chen <[email protected]>
Cc: Daniel Jordan <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: Jane Chu <[email protected]>
Cc: Paul E. McKenney <[email protected]>
Cc: Randy Dunlap <[email protected]>
Cc: Steffen Klassert <[email protected]>
Cc: Alexey Dobriyan <[email protected]>
Cc: Mike Kravetz <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

0 files changed, 0 insertions, 0 deletions