> From: Lorenzo Bianconi <lorenzo@xxxxxxxxxx> > Date: Fri, 12 May 2023 15:08:13 +0200 > > > In order to reduce page_pool memory footprint, rely on > > page_pool_dev_alloc_frag routine and reduce buffer size > > (VETH_PAGE_POOL_FRAG_SIZE) to PAGE_SIZE / 2 in order to consume one page > > for two 1500B frames. Reduce VETH_XDP_PACKET_HEADROOM to 192 from 256 > > (XDP_PACKET_HEADROOM) to fit max_head_size in VETH_PAGE_POOL_FRAG_SIZE. > > Please note, using default values (CONFIG_MAX_SKB_FRAGS=17), maximum > > supported MTU is now reduced to 36350B. > > I thought we're stepping away from page splitting bit by bit O_o do you mean to driver private page_split implementation? AFAIK we are not stepping away from page_pool page split implementation (or maybe I missed it :)) > Primarily for the reasons you mentioned / worked around here: it creates > several significant limitations and at least on 64-bit systems it > doesn't scale anymore. 192 bytes of headroom is less than what XDP > expects (isn't it? Isn't 256 standard-standard, so that skb XDP path > reallocates heads only to have 256+ there?), 384 bytes of shinfo can > change anytime and even now page split simply blocks you from increasing > MAX_SKB_FRAGS even by one. Not speaking of MTU limitations etc. > BTW Intel drivers suffer from the very same things due solely to page > split (and I'm almost done with converting at least some of them to Page > Pool and 1 page per buffer model), I don't recommend deliberately > falling into that pit =\ :D I am not sure about the 192 vs 256 bytes of headroom (this is why I sent this patch as RFC, my main goal is to discuss about this requirement). In the previous discussion [0] we deferred this implementation since if we do not reduce requested xdp headroom, we will not be able to fit two 1500B frames into a single page (for skb_shared_info size [1]) and we introduce a performance penalty. Regards, Lorenzo [0] https://lore.kernel.org/netdev/6298f73f7cc7391c7c4a52a6a89b1ae21488bda1.1682188837.git.lorenzo@xxxxxxxxxx/ [1] $ pahole -C skb_shared_info vmlinux.o struct skb_shared_info { __u8 flags; /* 0 1 */ __u8 meta_len; /* 1 1 */ __u8 nr_frags; /* 2 1 */ __u8 tx_flags; /* 3 1 */ unsigned short gso_size; /* 4 2 */ unsigned short gso_segs; /* 6 2 */ struct sk_buff * frag_list; /* 8 8 */ struct skb_shared_hwtstamps hwtstamps; /* 16 8 */ unsigned int gso_type; /* 24 4 */ u32 tskey; /* 28 4 */ atomic_t dataref; /* 32 4 */ unsigned int xdp_frags_size; /* 36 4 */ void * destructor_arg; /* 40 8 */ skb_frag_t frags[17]; /* 48 272 */ /* size: 320, cachelines: 5, members: 14 */ }; > > > > > Signed-off-by: Lorenzo Bianconi <lorenzo@xxxxxxxxxx> > > --- > > drivers/net/veth.c | 39 +++++++++++++++++++++++++-------------- > > 1 file changed, 25 insertions(+), 14 deletions(-) > [...] > > Thanks, > Olek
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