diff options
Diffstat (limited to 'mm/page_frag_cache.c')
| -rw-r--r-- | mm/page_frag_cache.c | 171 |
1 files changed, 171 insertions, 0 deletions
diff --git a/mm/page_frag_cache.c b/mm/page_frag_cache.c new file mode 100644 index 000000000000..3f7a203d35c6 --- /dev/null +++ b/mm/page_frag_cache.c @@ -0,0 +1,171 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* Page fragment allocator + * + * Page Fragment: + * An arbitrary-length arbitrary-offset area of memory which resides within a + * 0 or higher order page. Multiple fragments within that page are + * individually refcounted, in the page's reference counter. + * + * The page_frag functions provide a simple allocation framework for page + * fragments. This is used by the network stack and network device drivers to + * provide a backing region of memory for use as either an sk_buff->head, or to + * be used in the "frags" portion of skb_shared_info. + */ + +#include <linux/build_bug.h> +#include <linux/export.h> +#include <linux/gfp_types.h> +#include <linux/init.h> +#include <linux/mm.h> +#include <linux/page_frag_cache.h> +#include "internal.h" + +static unsigned long encoded_page_create(struct page *page, unsigned int order, + bool pfmemalloc) +{ + BUILD_BUG_ON(PAGE_FRAG_CACHE_MAX_ORDER > PAGE_FRAG_CACHE_ORDER_MASK); + BUILD_BUG_ON(PAGE_FRAG_CACHE_PFMEMALLOC_BIT >= PAGE_SIZE); + + return (unsigned long)page_address(page) | + (order & PAGE_FRAG_CACHE_ORDER_MASK) | + ((unsigned long)pfmemalloc * PAGE_FRAG_CACHE_PFMEMALLOC_BIT); +} + +static unsigned long encoded_page_decode_order(unsigned long encoded_page) +{ + return encoded_page & PAGE_FRAG_CACHE_ORDER_MASK; +} + +static void *encoded_page_decode_virt(unsigned long encoded_page) +{ + return (void *)(encoded_page & PAGE_MASK); +} + +static struct page *encoded_page_decode_page(unsigned long encoded_page) +{ + return virt_to_page((void *)encoded_page); +} + +static struct page *__page_frag_cache_refill(struct page_frag_cache *nc, + gfp_t gfp_mask) +{ + unsigned long order = PAGE_FRAG_CACHE_MAX_ORDER; + struct page *page = NULL; + gfp_t gfp = gfp_mask; + +#if (PAGE_SIZE < PAGE_FRAG_CACHE_MAX_SIZE) + gfp_mask = (gfp_mask & ~__GFP_DIRECT_RECLAIM) | __GFP_COMP | + __GFP_NOWARN | __GFP_NORETRY | __GFP_NOMEMALLOC; + page = __alloc_pages(gfp_mask, PAGE_FRAG_CACHE_MAX_ORDER, + numa_mem_id(), NULL); +#endif + if (unlikely(!page)) { + page = __alloc_pages(gfp, 0, numa_mem_id(), NULL); + order = 0; + } + + nc->encoded_page = page ? + encoded_page_create(page, order, page_is_pfmemalloc(page)) : 0; + + return page; +} + +void page_frag_cache_drain(struct page_frag_cache *nc) +{ + if (!nc->encoded_page) + return; + + __page_frag_cache_drain(encoded_page_decode_page(nc->encoded_page), + nc->pagecnt_bias); + nc->encoded_page = 0; +} +EXPORT_SYMBOL(page_frag_cache_drain); + +void __page_frag_cache_drain(struct page *page, unsigned int count) +{ + VM_BUG_ON_PAGE(page_ref_count(page) == 0, page); + + if (page_ref_sub_and_test(page, count)) + free_unref_page(page, compound_order(page)); +} +EXPORT_SYMBOL(__page_frag_cache_drain); + +void *__page_frag_alloc_align(struct page_frag_cache *nc, + unsigned int fragsz, gfp_t gfp_mask, + unsigned int align_mask) +{ + unsigned long encoded_page = nc->encoded_page; + unsigned int size, offset; + struct page *page; + + if (unlikely(!encoded_page)) { +refill: + page = __page_frag_cache_refill(nc, gfp_mask); + if (!page) + return NULL; + + encoded_page = nc->encoded_page; + + /* Even if we own the page, we do not use atomic_set(). + * This would break get_page_unless_zero() users. + */ + page_ref_add(page, PAGE_FRAG_CACHE_MAX_SIZE); + + /* reset page count bias and offset to start of new frag */ + nc->pagecnt_bias = PAGE_FRAG_CACHE_MAX_SIZE + 1; + nc->offset = 0; + } + + size = PAGE_SIZE << encoded_page_decode_order(encoded_page); + offset = __ALIGN_KERNEL_MASK(nc->offset, ~align_mask); + if (unlikely(offset + fragsz > size)) { + if (unlikely(fragsz > PAGE_SIZE)) { + /* + * The caller is trying to allocate a fragment + * with fragsz > PAGE_SIZE but the cache isn't big + * enough to satisfy the request, this may + * happen in low memory conditions. + * We don't release the cache page because + * it could make memory pressure worse + * so we simply return NULL here. + */ + return NULL; + } + + page = encoded_page_decode_page(encoded_page); + + if (!page_ref_sub_and_test(page, nc->pagecnt_bias)) + goto refill; + + if (unlikely(encoded_page_decode_pfmemalloc(encoded_page))) { + free_unref_page(page, + encoded_page_decode_order(encoded_page)); + goto refill; + } + + /* OK, page count is 0, we can safely set it */ + set_page_count(page, PAGE_FRAG_CACHE_MAX_SIZE + 1); + + /* reset page count bias and offset to start of new frag */ + nc->pagecnt_bias = PAGE_FRAG_CACHE_MAX_SIZE + 1; + offset = 0; + } + + nc->pagecnt_bias--; + nc->offset = offset + fragsz; + + return encoded_page_decode_virt(encoded_page) + offset; +} +EXPORT_SYMBOL(__page_frag_alloc_align); + +/* + * Frees a page fragment allocated out of either a compound or order 0 page. + */ +void page_frag_free(void *addr) +{ + struct page *page = virt_to_head_page(addr); + + if (unlikely(put_page_testzero(page))) + free_unref_page(page, compound_order(page)); +} +EXPORT_SYMBOL(page_frag_free); |