Messages in this thread | | | Date | Thu, 28 Apr 2011 20:47:55 +1000 | From | NeilBrown <> | Subject | Re: [PATCH 08/13] netvm: Allow skb allocation to use PFMEMALLOC reserves |
| |
On Thu, 28 Apr 2011 11:05:06 +0100 Mel Gorman <mgorman@suse.de> wrote:
> On Thu, Apr 28, 2011 at 04:19:33PM +1000, NeilBrown wrote: > > On Wed, 27 Apr 2011 17:08:06 +0100 Mel Gorman <mgorman@suse.de> wrote: > > > > > > > @@ -1578,7 +1589,7 @@ static inline struct sk_buff *netdev_alloc_skb_ip_align(struct net_device *dev, > > > */ > > > static inline struct page *__netdev_alloc_page(struct net_device *dev, gfp_t gfp_mask) > > > { > > > - return alloc_pages_node(NUMA_NO_NODE, gfp_mask, 0); > > > + return alloc_pages_node(NUMA_NO_NODE, gfp_mask | __GFP_MEMALLOC, 0); > > > } > > > > > > > I'm puzzling a bit over this change. > > __netdev_alloc_page appears to be used to get pages to put in ring buffer > > for a network card to DMA received packets into. So it is OK to use > > __GFP_MEMALLOC for these allocations providing we mark the resulting skb as > > 'pfmemalloc' if a reserved page was used. > > > > However I don't see where that marking is done. > > I think it should be in skb_fill_page_desc, something like: > > > > if (page->pfmemalloc) > > skb->pfmemalloc = true; > > > > Is this covered somewhere else that I am missing? > > > > You're not missing anything. > > >From the context of __netdev_alloc_page, we do not know if the skb > is suitable for marking pfmemalloc or not (we don't have SKB_ALLOC_RX > flag for example that __alloc_skb has). The reserves are potentially > being dipped into for an unsuitable packet but it gets dropped in > __netif_receive_skb() and the memory is returned. If we mark the skb > pfmemalloc as a result of __netdev_alloc_page using a reserve page, the > packets would not get dropped as expected. >
The only code in __netif_receive_skb that seems to drop packets is
+ if (skb_pfmemalloc(skb) && !skb_pfmemalloc_protocol(skb)) + goto drop; +
which requires that the skb have pfmemalloc set before it will be dropped.
Actually ... I'm expecting to find code that says: if (skb_pfmalloc(skb) && !sock_flag(sk, SOCK_MEMALLOC)) drop_packet();
but I cannot find it. Where is the code that discard pfmalloc packets for non-memalloc sockets?
I can see similar code in sk_filter but that doesn't drop the packet, it just avoids filtering it.
NeilBrown
| |