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Merge tag 'mm-nonmm-stable-2024-11-24-02-05' of git://git.kernel.org/…
…pub/scm/linux/kernel/git/akpm/mm Pull non-MM updates from Andrew Morton: - The series "resource: A couple of cleanups" from Andy Shevchenko performs some cleanups in the resource management code - The series "Improve the copy of task comm" from Yafang Shao addresses possible race-induced overflows in the management of task_struct.comm[] - The series "Remove unnecessary header includes from {tools/}lib/list_sort.c" from Kuan-Wei Chiu adds some cleanups and a small fix to the list_sort library code and to its selftest - The series "Enhance min heap API with non-inline functions and optimizations" also from Kuan-Wei Chiu optimizes and cleans up the min_heap library code - The series "nilfs2: Finish folio conversion" from Ryusuke Konishi finishes off nilfs2's folioification - The series "add detect count for hung tasks" from Lance Yang adds more userspace visibility into the hung-task detector's activity - Apart from that, singelton patches in many places - please see the individual changelogs for details * tag 'mm-nonmm-stable-2024-11-24-02-05' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm: (71 commits) gdb: lx-symbols: do not error out on monolithic build kernel/reboot: replace sprintf() with sysfs_emit() lib: util_macros_kunit: add kunit test for util_macros.h util_macros.h: fix/rework find_closest() macros Improve consistency of '#error' directive messages ocfs2: fix uninitialized value in ocfs2_file_read_iter() hung_task: add docs for hung_task_detect_count hung_task: add detect count for hung tasks dma-buf: use atomic64_inc_return() in dma_buf_getfile() fs/proc/kcore.c: fix coccinelle reported ERROR instances resource: avoid unnecessary resource tree walking in __region_intersects() ocfs2: remove unused errmsg function and table ocfs2: cluster: fix a typo lib/scatterlist: use sg_phys() helper checkpatch: always parse orig_commit in fixes tag nilfs2: convert metadata aops from writepage to writepages nilfs2: convert nilfs_recovery_copy_block() to take a folio nilfs2: convert nilfs_page_count_clean_buffers() to take a folio nilfs2: remove nilfs_writepage nilfs2: convert checkpoint file to be folio-based ...
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.. SPDX-License-Identifier: GPL-2.0 | ||
============ | ||
Min Heap API | ||
============ | ||
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Introduction | ||
============ | ||
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The Min Heap API provides a set of functions and macros for managing min-heaps | ||
in the Linux kernel. A min-heap is a binary tree structure where the value of | ||
each node is less than or equal to the values of its children, ensuring that | ||
the smallest element is always at the root. | ||
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||
This document provides a guide to the Min Heap API, detailing how to define and | ||
use min-heaps. Users should not directly call functions with **__min_heap_*()** | ||
prefixes, but should instead use the provided macro wrappers. | ||
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||
In addition to the standard version of the functions, the API also includes a | ||
set of inline versions for performance-critical scenarios. These inline | ||
functions have the same names as their non-inline counterparts but include an | ||
**_inline** suffix. For example, **__min_heap_init_inline** and its | ||
corresponding macro wrapper **min_heap_init_inline**. The inline versions allow | ||
custom comparison and swap functions to be called directly, rather than through | ||
indirect function calls. This can significantly reduce overhead, especially | ||
when CONFIG_MITIGATION_RETPOLINE is enabled, as indirect function calls become | ||
more expensive. As with the non-inline versions, it is important to use the | ||
macro wrappers for inline functions instead of directly calling the functions | ||
themselves. | ||
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||
Data Structures | ||
=============== | ||
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Min-Heap Definition | ||
------------------- | ||
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||
The core data structure for representing a min-heap is defined using the | ||
**MIN_HEAP_PREALLOCATED** and **DEFINE_MIN_HEAP** macros. These macros allow | ||
you to define a min-heap with a preallocated buffer or dynamically allocated | ||
memory. | ||
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Example: | ||
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.. code-block:: c | ||
#define MIN_HEAP_PREALLOCATED(_type, _name, _nr) | ||
struct _name { | ||
int nr; /* Number of elements in the heap */ | ||
int size; /* Maximum number of elements that can be held */ | ||
_type *data; /* Pointer to the heap data */ | ||
_type preallocated[_nr]; /* Static preallocated array */ | ||
} | ||
#define DEFINE_MIN_HEAP(_type, _name) MIN_HEAP_PREALLOCATED(_type, _name, 0) | ||
A typical heap structure will include a counter for the number of elements | ||
(`nr`), the maximum capacity of the heap (`size`), and a pointer to an array of | ||
elements (`data`). Optionally, you can specify a static array for preallocated | ||
heap storage using **MIN_HEAP_PREALLOCATED**. | ||
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Min Heap Callbacks | ||
------------------ | ||
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The **struct min_heap_callbacks** provides customization options for ordering | ||
elements in the heap and swapping them. It contains two function pointers: | ||
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.. code-block:: c | ||
struct min_heap_callbacks { | ||
bool (*less)(const void *lhs, const void *rhs, void *args); | ||
void (*swp)(void *lhs, void *rhs, void *args); | ||
}; | ||
- **less** is the comparison function used to establish the order of elements. | ||
- **swp** is a function for swapping elements in the heap. If swp is set to | ||
NULL, the default swap function will be used, which swaps the elements based on their size | ||
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Macro Wrappers | ||
============== | ||
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The following macro wrappers are provided for interacting with the heap in a | ||
user-friendly manner. Each macro corresponds to a function that operates on the | ||
heap, and they abstract away direct calls to internal functions. | ||
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Each macro accepts various parameters that are detailed below. | ||
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Heap Initialization | ||
-------------------- | ||
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.. code-block:: c | ||
min_heap_init(heap, data, size); | ||
- **heap**: A pointer to the min-heap structure to be initialized. | ||
- **data**: A pointer to the buffer where the heap elements will be stored. If | ||
`NULL`, the preallocated buffer within the heap structure will be used. | ||
- **size**: The maximum number of elements the heap can hold. | ||
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This macro initializes the heap, setting its initial state. If `data` is | ||
`NULL`, the preallocated memory inside the heap structure will be used for | ||
storage. Otherwise, the user-provided buffer is used. The operation is **O(1)**. | ||
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**Inline Version:** min_heap_init_inline(heap, data, size) | ||
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Accessing the Top Element | ||
------------------------- | ||
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.. code-block:: c | ||
element = min_heap_peek(heap); | ||
- **heap**: A pointer to the min-heap from which to retrieve the smallest | ||
element. | ||
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This macro returns a pointer to the smallest element (the root) of the heap, or | ||
`NULL` if the heap is empty. The operation is **O(1)**. | ||
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**Inline Version:** min_heap_peek_inline(heap) | ||
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Heap Insertion | ||
-------------- | ||
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.. code-block:: c | ||
success = min_heap_push(heap, element, callbacks, args); | ||
- **heap**: A pointer to the min-heap into which the element should be inserted. | ||
- **element**: A pointer to the element to be inserted into the heap. | ||
- **callbacks**: A pointer to a `struct min_heap_callbacks` providing the | ||
`less` and `swp` functions. | ||
- **args**: Optional arguments passed to the `less` and `swp` functions. | ||
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This macro inserts an element into the heap. It returns `true` if the insertion | ||
was successful and `false` if the heap is full. The operation is **O(log n)**. | ||
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**Inline Version:** min_heap_push_inline(heap, element, callbacks, args) | ||
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Heap Removal | ||
------------ | ||
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.. code-block:: c | ||
success = min_heap_pop(heap, callbacks, args); | ||
- **heap**: A pointer to the min-heap from which to remove the smallest element. | ||
- **callbacks**: A pointer to a `struct min_heap_callbacks` providing the | ||
`less` and `swp` functions. | ||
- **args**: Optional arguments passed to the `less` and `swp` functions. | ||
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This macro removes the smallest element (the root) from the heap. It returns | ||
`true` if the element was successfully removed, or `false` if the heap is | ||
empty. The operation is **O(log n)**. | ||
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**Inline Version:** min_heap_pop_inline(heap, callbacks, args) | ||
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Heap Maintenance | ||
---------------- | ||
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You can use the following macros to maintain the heap's structure: | ||
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.. code-block:: c | ||
min_heap_sift_down(heap, pos, callbacks, args); | ||
- **heap**: A pointer to the min-heap. | ||
- **pos**: The index from which to start sifting down. | ||
- **callbacks**: A pointer to a `struct min_heap_callbacks` providing the | ||
`less` and `swp` functions. | ||
- **args**: Optional arguments passed to the `less` and `swp` functions. | ||
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This macro restores the heap property by moving the element at the specified | ||
index (`pos`) down the heap until it is in the correct position. The operation | ||
is **O(log n)**. | ||
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**Inline Version:** min_heap_sift_down_inline(heap, pos, callbacks, args) | ||
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.. code-block:: c | ||
min_heap_sift_up(heap, idx, callbacks, args); | ||
- **heap**: A pointer to the min-heap. | ||
- **idx**: The index of the element to sift up. | ||
- **callbacks**: A pointer to a `struct min_heap_callbacks` providing the | ||
`less` and `swp` functions. | ||
- **args**: Optional arguments passed to the `less` and `swp` functions. | ||
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This macro restores the heap property by moving the element at the specified | ||
index (`idx`) up the heap. The operation is **O(log n)**. | ||
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**Inline Version:** min_heap_sift_up_inline(heap, idx, callbacks, args) | ||
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.. code-block:: c | ||
min_heapify_all(heap, callbacks, args); | ||
- **heap**: A pointer to the min-heap. | ||
- **callbacks**: A pointer to a `struct min_heap_callbacks` providing the | ||
`less` and `swp` functions. | ||
- **args**: Optional arguments passed to the `less` and `swp` functions. | ||
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This macro ensures that the entire heap satisfies the heap property. It is | ||
called when the heap is built from scratch or after many modifications. The | ||
operation is **O(n)**. | ||
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**Inline Version:** min_heapify_all_inline(heap, callbacks, args) | ||
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Removing Specific Elements | ||
-------------------------- | ||
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.. code-block:: c | ||
success = min_heap_del(heap, idx, callbacks, args); | ||
- **heap**: A pointer to the min-heap. | ||
- **idx**: The index of the element to delete. | ||
- **callbacks**: A pointer to a `struct min_heap_callbacks` providing the | ||
`less` and `swp` functions. | ||
- **args**: Optional arguments passed to the `less` and `swp` functions. | ||
|
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This macro removes an element at the specified index (`idx`) from the heap and | ||
restores the heap property. The operation is **O(log n)**. | ||
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**Inline Version:** min_heap_del_inline(heap, idx, callbacks, args) | ||
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Other Utilities | ||
=============== | ||
|
||
- **min_heap_full(heap)**: Checks whether the heap is full. | ||
Complexity: **O(1)**. | ||
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.. code-block:: c | ||
bool full = min_heap_full(heap); | ||
- `heap`: A pointer to the min-heap to check. | ||
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This macro returns `true` if the heap is full, otherwise `false`. | ||
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**Inline Version:** min_heap_full_inline(heap) | ||
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- **min_heap_empty(heap)**: Checks whether the heap is empty. | ||
Complexity: **O(1)**. | ||
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.. code-block:: c | ||
bool empty = min_heap_empty(heap); | ||
- `heap`: A pointer to the min-heap to check. | ||
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This macro returns `true` if the heap is empty, otherwise `false`. | ||
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**Inline Version:** min_heap_empty_inline(heap) | ||
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Example Usage | ||
============= | ||
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An example usage of the min-heap API would involve defining a heap structure, | ||
initializing it, and inserting and removing elements as needed. | ||
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.. code-block:: c | ||
#include <linux/min_heap.h> | ||
int my_less_function(const void *lhs, const void *rhs, void *args) { | ||
return (*(int *)lhs < *(int *)rhs); | ||
} | ||
struct min_heap_callbacks heap_cb = { | ||
.less = my_less_function, /* Comparison function for heap order */ | ||
.swp = NULL, /* Use default swap function */ | ||
}; | ||
void example_usage(void) { | ||
/* Pre-populate the buffer with elements */ | ||
int buffer[5] = {5, 2, 8, 1, 3}; | ||
/* Declare a min-heap */ | ||
DEFINE_MIN_HEAP(int, my_heap); | ||
/* Initialize the heap with preallocated buffer and size */ | ||
min_heap_init(&my_heap, buffer, 5); | ||
/* Build the heap using min_heapify_all */ | ||
my_heap.nr = 5; /* Set the number of elements in the heap */ | ||
min_heapify_all(&my_heap, &heap_cb, NULL); | ||
/* Peek at the top element (should be 1 in this case) */ | ||
int *top = min_heap_peek(&my_heap); | ||
pr_info("Top element: %d\n", *top); | ||
/* Pop the top element (1) and get the new top (2) */ | ||
min_heap_pop(&my_heap, &heap_cb, NULL); | ||
top = min_heap_peek(&my_heap); | ||
pr_info("New top element: %d\n", *top); | ||
/* Insert a new element (0) and recheck the top */ | ||
int new_element = 0; | ||
min_heap_push(&my_heap, &new_element, &heap_cb, NULL); | ||
top = min_heap_peek(&my_heap); | ||
pr_info("Top element after insertion: %d\n", *top); | ||
} |
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