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Message-ID: <1286813133.2737.36.camel@edumazet-laptop> Date: Mon, 11 Oct 2010 18:05:33 +0200 From: Eric Dumazet <eric.dumazet@...il.com> To: Stanislaw Gruszka <sgruszka@...hat.com> Cc: David Miller <davem@...emloft.net>, Francois Romieu <romieu@...zoreil.com>, netdev@...r.kernel.org Subject: Re: [PATCH] net: introduce alloc_skb_order0 Le lundi 11 octobre 2010 à 17:55 +0200, Stanislaw Gruszka a écrit : > On Sat, Oct 09, 2010 at 05:59:56PM +0200, Eric Dumazet wrote: > > Le vendredi 08 octobre 2010 à 18:03 +0200, Stanislaw Gruszka a écrit : > > > On Fri, Oct 08, 2010 at 05:04:07PM +0200, Eric Dumazet wrote: > > > > > > Switch to SLAB -> no more problem ;) > > > > > > yeh, I wish to, but fedora use SLUB because of some debugging > > > capabilities. > > > > Yes, of course, I was kidding :) > > > > echo 0 >/sys/kernel/slab/kmalloc-2048/order > > echo 0 >/sys/kernel/slab/kmalloc-1024/order > > echo 0 >/sys/kernel/slab/kmalloc-512/order > > > > Should do the trick : No more high order allocations for MTU=1500 > > frames. > > So the SLUB is great, but we need a patch to avoid using it :-) > > > For MTU=9000 frames, we probably need something like this patch : > > > > Reception of big frames hit a memory allocation problem, because of high > > order pages allocations (order-3 sometimes for MTU=9000). This patch > > introduces alloc_skb_order0(), to build skbs with order-0 pages only. > > I had never seen allocation problems in rtl8169_try_rx_copy or in any > other driver rx path (except iwlwifi, but now this is solved by using > skb_add_rx_frag), so I'm not sure if need this patch. > > However I see other benefit of that patch. We save memory. Allocating > for MTU 9000 gives something like skb->data = kmalloc(9000 + 32 + 2 > + 334). So we take data from kmalloc-16384 cache, we waste about 7kB on > every allocation. With patch wastage would be about 2k per allocation > (assuming 4kB and 8kB page size) > > However I started this thread thinking about other memory wastage, > in rtl8169_alloc_rx_skb, skb->data = kmalloc(16383 + 32 + 2 + 334), taken > from kmalloc-32768, almost 50% wastage. > You cannot use my patch to avoid this waste. Really. You have two different things in this driver : 1) Allocation of a physically continous 16Kbytes bloc for the rx-ring, at device initialization (GFP_KERNEL OK here) Here, the only thing you could do is to not allocate real skbs but only 16KB data blocs (no need for the sk_buf, only the ->data part), and force copybreak for all incoming packets (remove the rx_copybreak tunable) 2) Allocation of order0 skb to perform the copybreak in rx path. (GFP_ATOMIC) : My patch. > > +struct sk_buff *alloc_skb_order0(int pkt_size) > > +{ > > + int head = min_t(int, pkt_size, SKB_MAX_HEAD(NET_SKB_PAD + NET_IP_ALIGN)); > > + struct sk_buff *skb; > > + > > + skb = alloc_skb(head + NET_SKB_PAD + NET_IP_ALIGN, > > + GFP_ATOMIC | __GFP_NOWARN); > > + if (!skb) > > + return NULL; > > + skb_reserve(skb, NET_SKB_PAD + NET_IP_ALIGN); > > + skb_put(skb, head); > > + pkt_size -= head; > > + > > + skb->len += pkt_size; > > + skb->data_len += pkt_size; > > + skb->truesize += pkt_size; > > + while (pkt_size) { > > if (skb_shinfo(skb)->nr_frags == MAX_SKB_FRAGS - 1) > goto error; Not needed. A frame is < 16383 bytes, so _must_ fit in an skb, (skb can hold up to 64 Kbytes) > > > + int i = skb_shinfo(skb)->nr_frags++; > > + skb_frag_t *frag = &skb_shinfo(skb)->frags[i]; > > + int fragsize = min_t(int, pkt_size, PAGE_SIZE); > > + struct page *page = alloc_page(GFP_NOWAIT | __GFP_NOWARN); > > + > > + if (!page) > > + goto error; > > + frag->page = page; > > + frag->size = fragsize; > > + frag->page_offset = 0; > > + pkt_size -= fragsize; > > + } > > + return skb; > > + > > +error: > > + kfree_skb(skb); > > + return NULL; > > +} > > +EXPORT_SYMBOL(alloc_skb_order0); > > + > > /* Checksum skb data. */ > > > > __wsum skb_checksum(const struct sk_buff *skb, int offset, -- 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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