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On most architectures division is an expensive operation and accessing an element currently requires four of them. This performance penalty effectively precludes flex arrays from being used on any kind of fast path. However, two of these divisions can be handled at creation time and the others can be replaced by a reciprocal divide, completely avoiding real divisions on access. [eparis@redhat.com: rebase on top of changes to support 0 len elements] [eparis@redhat.com: initialize part_nr when array fits entirely in base] Signed-off-by: Jesse Gross <jesse@nicira.com> Signed-off-by: Eric Paris <eparis@redhat.com> Cc: Dave Hansen <dave@linux.vnet.ibm.com> Cc: David Rientjes <rientjes@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
81 lines
2.4 KiB
C
81 lines
2.4 KiB
C
#ifndef _FLEX_ARRAY_H
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#define _FLEX_ARRAY_H
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#include <linux/types.h>
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#include <asm/page.h>
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#define FLEX_ARRAY_PART_SIZE PAGE_SIZE
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#define FLEX_ARRAY_BASE_SIZE PAGE_SIZE
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struct flex_array_part;
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/*
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* This is meant to replace cases where an array-like
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* structure has gotten too big to fit into kmalloc()
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* and the developer is getting tempted to use
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* vmalloc().
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*/
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struct flex_array {
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union {
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struct {
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int element_size;
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int total_nr_elements;
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int elems_per_part;
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u32 reciprocal_elems;
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struct flex_array_part *parts[];
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};
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/*
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* This little trick makes sure that
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* sizeof(flex_array) == PAGE_SIZE
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*/
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char padding[FLEX_ARRAY_BASE_SIZE];
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};
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};
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/* Number of bytes left in base struct flex_array, excluding metadata */
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#define FLEX_ARRAY_BASE_BYTES_LEFT \
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(FLEX_ARRAY_BASE_SIZE - offsetof(struct flex_array, parts))
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/* Number of pointers in base to struct flex_array_part pages */
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#define FLEX_ARRAY_NR_BASE_PTRS \
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(FLEX_ARRAY_BASE_BYTES_LEFT / sizeof(struct flex_array_part *))
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/* Number of elements of size that fit in struct flex_array_part */
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#define FLEX_ARRAY_ELEMENTS_PER_PART(size) \
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(FLEX_ARRAY_PART_SIZE / size)
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/*
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* Defines a statically allocated flex array and ensures its parameters are
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* valid.
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*/
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#define DEFINE_FLEX_ARRAY(__arrayname, __element_size, __total) \
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struct flex_array __arrayname = { { { \
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.element_size = (__element_size), \
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.total_nr_elements = (__total), \
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} } }; \
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static inline void __arrayname##_invalid_parameter(void) \
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{ \
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BUILD_BUG_ON((__total) > FLEX_ARRAY_NR_BASE_PTRS * \
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FLEX_ARRAY_ELEMENTS_PER_PART(__element_size)); \
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}
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struct flex_array *flex_array_alloc(int element_size, unsigned int total,
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gfp_t flags);
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int flex_array_prealloc(struct flex_array *fa, unsigned int start,
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unsigned int nr_elements, gfp_t flags);
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void flex_array_free(struct flex_array *fa);
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void flex_array_free_parts(struct flex_array *fa);
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int flex_array_put(struct flex_array *fa, unsigned int element_nr, void *src,
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gfp_t flags);
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int flex_array_clear(struct flex_array *fa, unsigned int element_nr);
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void *flex_array_get(struct flex_array *fa, unsigned int element_nr);
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int flex_array_shrink(struct flex_array *fa);
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#define flex_array_put_ptr(fa, nr, src, gfp) \
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flex_array_put(fa, nr, (void *)&(src), gfp)
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void *flex_array_get_ptr(struct flex_array *fa, unsigned int element_nr);
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#endif /* _FLEX_ARRAY_H */
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