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Date: Thu, 28 Aug 2014 14:34:03 -0700 From: Eric Dumazet <eric.dumazet@...il.com> To: Shmulik Ladkani <sladkani@...co.com> Cc: Mel Gorman <mgorman@...e.de>, Neil Brown <neilb@...e.de>, "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org Subject: Re: Concerns regarding PFMEMALLOC handling in __netdev_alloc_skb On Thu, 2014-08-28 at 23:23 +0300, Shmulik Ladkani wrote: > 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? This was discussed few days ago. http://www.spinics.net/lists/netdev/msg293334.html http://www.spinics.net/lists/netdev/msg293336.html You should sync with Govindarajulu Varadarajan to cook a proper patch. -- 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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