Linux-mm

GeeP organized tutorial on

Linux-mm APIs : A brief tutorial Amey Inamdar Infrastructure sponsors: Oasis Technologies

A quick brushup • Virtual Memory • Paging

Virtual Memory Layout

Buddy/Zone allocator • Zones: – ZONE_DMA – ZONE_NORMAL – ZONE_HIGHMEM

0 – 16 MB 16-896 MB 896 MB onwards

• Buddy allocator – Working – APIs struct page * alloc_pages(gfp_t gfp_mask, unsigned int order); void free_pages(unsigned long addr, unsigned int order);

Vmalloc & Highmem • Page aligned virtually contiguous memory • Pages can be physically non-contiguous • APIs – void *vmalloc(unsigned long size); – void vfree(void *addr);

• Kmap & highmem – void *kmap(struct page *page); – void kunmap(struct page *page); – void *kmap_atomic(struct page *page, enum km_type type);

Slab allocator • What about small sized allocations e.g. for structure instances? • Layer which gets the pages from zone/buddy allocator and satisfies small sized allocations. • Brief working

Slab allocator (continued)

Slab Allocator - APIs •

struct kmem_cache * kmem_cache_create( const char *name, size_t size, size_t align, unsigned long flags; void (*ctor)(void*, struct kmem_cache *, unsigned long), void (*dtor)(void*, struct kmem_cache *, unsigned long));

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void kmem_cache_destroy( struct kmem_cache *cachep );

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void kmem_cache_alloc( struct kmem_cache *cachep, gfp_t flags );

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void kmem_cache_free( struct kmem_cache *cachep, void *objp );

Slab allocator - APIs • General purpose cache • APIs – void *kmalloc( size_t size, int flags ); – void kfree( const void *objp );