From 69b08f62e17439ee3d436faf0b9a7ca6fffb78db Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Wed, 26 Sep 2012 06:46:57 +0000 Subject: [PATCH] net: use bigger pages in __netdev_alloc_frag We currently use percpu order-0 pages in __netdev_alloc_frag to deliver fragments used by __netdev_alloc_skb() Depending on NIC driver and arch being 32 or 64 bit, it allows a page to be split in several fragments (between 1 and 8), assuming PAGE_SIZE=4096 Switching to bigger pages (32768 bytes for PAGE_SIZE=4096 case) allows : - Better filling of space (the ending hole overhead is less an issue) - Less calls to page allocator or accesses to page->_count - Could allow struct skb_shared_info futures changes without major performance impact. This patch implements a transparent fallback to smaller pages in case of memory pressure. It also uses a standard "struct page_frag" instead of a custom one. Signed-off-by: Eric Dumazet Cc: Alexander Duyck Cc: Benjamin LaHaise Signed-off-by: David S. Miller --- net/core/skbuff.c | 46 ++++++++++++++++++++++++++++++---------------- 1 file changed, 30 insertions(+), 16 deletions(-) diff --git a/net/core/skbuff.c b/net/core/skbuff.c index 2ede3cfa8ffa..607a70ff2cc2 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -340,43 +340,57 @@ struct sk_buff *build_skb(void *data, unsigned int frag_size) EXPORT_SYMBOL(build_skb); struct netdev_alloc_cache { - struct page *page; - unsigned int offset; - unsigned int pagecnt_bias; + struct page_frag frag; + /* we maintain a pagecount bias, so that we dont dirty cache line + * containing page->_count every time we allocate a fragment. + */ + unsigned int pagecnt_bias; }; static DEFINE_PER_CPU(struct netdev_alloc_cache, netdev_alloc_cache); -#define NETDEV_PAGECNT_BIAS (PAGE_SIZE / SMP_CACHE_BYTES) +#define NETDEV_FRAG_PAGE_MAX_ORDER get_order(32768) +#define NETDEV_FRAG_PAGE_MAX_SIZE (PAGE_SIZE << NETDEV_FRAG_PAGE_MAX_ORDER) +#define NETDEV_PAGECNT_MAX_BIAS NETDEV_FRAG_PAGE_MAX_SIZE static void *__netdev_alloc_frag(unsigned int fragsz, gfp_t gfp_mask) { struct netdev_alloc_cache *nc; void *data = NULL; + int order; unsigned long flags; local_irq_save(flags); nc = &__get_cpu_var(netdev_alloc_cache); - if (unlikely(!nc->page)) { + if (unlikely(!nc->frag.page)) { refill: - nc->page = alloc_page(gfp_mask); - if (unlikely(!nc->page)) - goto end; + for (order = NETDEV_FRAG_PAGE_MAX_ORDER; ;) { + gfp_t gfp = gfp_mask; + + if (order) + gfp |= __GFP_COMP | __GFP_NOWARN; + nc->frag.page = alloc_pages(gfp, order); + if (likely(nc->frag.page)) + break; + if (--order < 0) + goto end; + } + nc->frag.size = PAGE_SIZE << order; recycle: - atomic_set(&nc->page->_count, NETDEV_PAGECNT_BIAS); - nc->pagecnt_bias = NETDEV_PAGECNT_BIAS; - nc->offset = 0; + atomic_set(&nc->frag.page->_count, NETDEV_PAGECNT_MAX_BIAS); + nc->pagecnt_bias = NETDEV_PAGECNT_MAX_BIAS; + nc->frag.offset = 0; } - if (nc->offset + fragsz > PAGE_SIZE) { + if (nc->frag.offset + fragsz > nc->frag.size) { /* avoid unnecessary locked operations if possible */ - if ((atomic_read(&nc->page->_count) == nc->pagecnt_bias) || - atomic_sub_and_test(nc->pagecnt_bias, &nc->page->_count)) + if ((atomic_read(&nc->frag.page->_count) == nc->pagecnt_bias) || + atomic_sub_and_test(nc->pagecnt_bias, &nc->frag.page->_count)) goto recycle; goto refill; } - data = page_address(nc->page) + nc->offset; - nc->offset += fragsz; + data = page_address(nc->frag.page) + nc->frag.offset; + nc->frag.offset += fragsz; nc->pagecnt_bias--; end: local_irq_restore(flags); -- 2.20.1