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Diffstat (limited to 'Documentation/core-api/memory-allocation.rst')
| -rw-r--r-- | Documentation/core-api/memory-allocation.rst | 28 |
1 files changed, 20 insertions, 8 deletions
diff --git a/Documentation/core-api/memory-allocation.rst b/Documentation/core-api/memory-allocation.rst index 5954ddf6ee13..0f19dd524323 100644 --- a/Documentation/core-api/memory-allocation.rst +++ b/Documentation/core-api/memory-allocation.rst @@ -45,8 +45,9 @@ here we briefly outline their recommended usage: * If the allocation is performed from an atomic context, e.g interrupt handler, use ``GFP_NOWAIT``. This flag prevents direct reclaim and IO or filesystem operations. Consequently, under memory pressure - ``GFP_NOWAIT`` allocation is likely to fail. Allocations which - have a reasonable fallback should be using ``GFP_NOWARN``. + ``GFP_NOWAIT`` allocation is likely to fail. Users of this flag need + to provide a suitable fallback to cope with such failures where + appropriate. * If you think that accessing memory reserves is justified and the kernel will be stressed unless allocation succeeds, you may use ``GFP_ATOMIC``. * Untrusted allocations triggered from userspace should be a subject @@ -144,8 +145,10 @@ configuration, but it is a good practice to use `kmalloc` for objects smaller than page size. The address of a chunk allocated with `kmalloc` is aligned to at least -ARCH_KMALLOC_MINALIGN bytes. For sizes which are a power of two, the -alignment is also guaranteed to be at least the respective size. +ARCH_KMALLOC_MINALIGN bytes. For sizes which are a power of two, the +alignment is also guaranteed to be at least the respective size. For other +sizes, the alignment is guaranteed to be at least the largest power-of-two +divisor of the size. Chunks allocated with kmalloc() can be resized with krealloc(). Similarly to kmalloc_array(): a helper for resizing arrays is provided in the form of @@ -170,7 +173,16 @@ should be used if a part of the cache might be copied to the userspace. After the cache is created kmem_cache_alloc() and its convenience wrappers can allocate memory from that cache. -When the allocated memory is no longer needed it must be freed. You can -use kvfree() for the memory allocated with `kmalloc`, `vmalloc` and -`kvmalloc`. The slab caches should be freed with kmem_cache_free(). And -don't forget to destroy the cache with kmem_cache_destroy(). +When the allocated memory is no longer needed it must be freed. + +Objects allocated by `kmalloc` can be freed by `kfree` or `kvfree`. Objects +allocated by `kmem_cache_alloc` can be freed with `kmem_cache_free`, `kfree` +or `kvfree`, where the latter two might be more convenient thanks to not +needing the kmem_cache pointer. + +The same rules apply to _bulk and _rcu flavors of freeing functions. + +Memory allocated by `vmalloc` can be freed with `vfree` or `kvfree`. +Memory allocated by `kvmalloc` can be freed with `kvfree`. +Caches created by `kmem_cache_create` should be freed with +`kmem_cache_destroy` only after freeing all the allocated objects first. |