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Date: Thu, 28 Aug 2014 23:23:50 +0300 From: Shmulik Ladkani <sladkani@...co.com> To: Mel Gorman <mgorman@...e.de> Cc: Neil Brown <neilb@...e.de>, Eric Dumazet <eric.dumazet@...il.com>, "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org Subject: Concerns regarding PFMEMALLOC handling in __netdev_alloc_skb Hi, >From c93bdd0e03 "netvm: allow skb allocation to use PFMEMALLOC reserves": @@ -366,7 +417,12 @@ struct sk_buff *__netdev_alloc_skb(struct net_device *dev, SKB_DATA_ALIGN(sizeof(struct skb_shared_info)); if (fragsz <= PAGE_SIZE && !(gfp_mask & (__GFP_WAIT | GFP_DMA))) { - void *data = netdev_alloc_frag(fragsz); + void *data; + + if (sk_memalloc_socks()) + gfp_mask |= __GFP_MEMALLOC; + + data = __netdev_alloc_frag(fragsz, gfp_mask); if (likely(data)) { skb = build_skb(data, fragsz); if (unlikely(!skb)) put_page(virt_to_head_page(data)); } } else { - skb = __alloc_skb(length + NET_SKB_PAD, gfp_mask, 0, NUMA_NO_NODE); + skb = __alloc_skb(length + NET_SKB_PAD, gfp_mask, + SKB_ALLOC_RX, NUMA_NO_NODE); } In the 'else' part, SKB_ALLOC_RX is provided to '__alloc_skb()'. Thus '__alloc_skb()' may attempt using the PFMEMALLOC reserve in case 'sk_memalloc_socks()' is true - and 'skb->pfmemalloc' will be set accordingly. Good. However, in the 'if' part, in case 'sk_memalloc_socks()' is true, __GFP_MEMALLOC is passed to '__netdev_alloc_frag()'. There are two possible issues here: 1. '__netdev_alloc_frag()' might not honour __GFP_MEMALLOC in case the frag fits into current netdev_alloc_cache.frag 2. Even if 'nc->frag.page' gets allocated/refilled, and __GFP_MEMALLOC is passed to 'alloc_pages()' - in case the new page is from the PFMEMALLOC reserve, that notion is not propagated to back to skb->pfmemalloc. Are these of any concern? Regards, Shmulik -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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