From: NeilBrown <neilb@suse.de>
To: Mel Gorman <mgorman@suse.de>
Cc: Linux-MM <linux-mm@kvack.org>,
Linux-Netdev <netdev@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
David Miller <davem@davemloft.net>,
Peter Zijlstra <a.p.zijlstra@chello.nl>
Subject: Re: [PATCH 08/13] netvm: Allow skb allocation to use PFMEMALLOC reserves
Date: Thu, 28 Apr 2011 20:47:55 +1000 [thread overview]
Message-ID: <20110428204755.2e07147e@notabene.brown> (raw)
In-Reply-To: <20110428100035.GO4658@suse.de>
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
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next prev parent reply other threads:[~2011-04-28 10:48 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-04-27 16:07 [PATCH 00/13] Swap-over-NBD without deadlocking v3 Mel Gorman
2011-04-27 16:07 ` [PATCH 01/13] mm: Serialize access to min_free_kbytes Mel Gorman
2011-04-27 16:08 ` [PATCH 02/13] mm: sl[au]b: Add knowledge of PFMEMALLOC reserve pages Mel Gorman
2011-04-27 16:08 ` [PATCH 03/13] mm: Introduce __GFP_MEMALLOC to allow access to emergency reserves Mel Gorman
2011-04-27 16:08 ` [PATCH 04/13] mm: allow PF_MEMALLOC from softirq context Mel Gorman
2011-04-27 16:08 ` [PATCH 05/13] mm: Ignore mempolicies when using ALLOC_NO_WATERMARK Mel Gorman
2011-04-27 16:08 ` [PATCH 06/13] net: Introduce sk_allocation() to allow addition of GFP flags depending on the individual socket Mel Gorman
2011-04-27 16:08 ` [PATCH 07/13] netvm: Allow the use of __GFP_MEMALLOC by specific sockets Mel Gorman
2011-04-27 16:08 ` [PATCH 08/13] netvm: Allow skb allocation to use PFMEMALLOC reserves Mel Gorman
2011-04-28 6:19 ` NeilBrown
2011-04-28 10:05 ` Mel Gorman
2011-04-28 10:47 ` NeilBrown [this message]
2011-04-28 11:18 ` Mel Gorman
2011-04-29 2:55 ` NeilBrown
2011-05-03 11:45 ` Mel Gorman
2011-04-27 16:08 ` [PATCH 09/13] netvm: Set PF_MEMALLOC as appropriate during SKB processing Mel Gorman
2011-04-27 16:08 ` [PATCH 10/13] mm: Micro-optimise slab to avoid a function call Mel Gorman
2011-04-27 16:08 ` [PATCH 11/13] nbd: Set SOCK_MEMALLOC for access to PFMEMALLOC reserves Mel Gorman
2011-04-27 16:08 ` [PATCH 12/13] mm: Throttle direct reclaimers if PF_MEMALLOC reserves are low and swap is backed by network storage Mel Gorman
2011-04-28 0:22 ` NeilBrown
2011-04-28 10:14 ` Mel Gorman
2011-04-27 16:08 ` [PATCH 13/13] mm: Account for the number of times direct reclaimers get throttled Mel Gorman
-- strict thread matches above, loose matches on Subject: below --
2011-04-26 7:36 [PATCH 00/13] Swap-over-NBD without deadlocking Mel Gorman
2011-04-26 7:36 ` [PATCH 08/13] netvm: Allow skb allocation to use PFMEMALLOC reserves Mel Gorman
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