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Message-ID: <20101011155556.GA2431@redhat.com> Date: Mon, 11 Oct 2010 17:55:57 +0200 From: Stanislaw Gruszka <sgruszka@...hat.com> To: Eric Dumazet <eric.dumazet@...il.com> Cc: David Miller <davem@...emloft.net>, Francois Romieu <romieu@...zoreil.com>, netdev@...r.kernel.org Subject: Re: [PATCH] net: introduce alloc_skb_order0 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. > +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; > + 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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