linux清理缓存cache_udp缓冲区满了,数据是否会丢失

struct sk_buff {
    /* These two members must be first. */
    struct sk_buff        *next;-------------有没有人想过为啥不用内核标准的list来，而是单独两个成员？如果你有好的想法，可以跟我讨论。
    struct sk_buff        *prev;
#ifdef __GENKSYMS__
    ktime_t        tstamp;
#else
    union {
        ktime_t        tstamp;
        struct skb_mstamp skb_mstamp;
    };
#endif
    struct sock        *sk;
    struct net_device    *dev;

    /*
     * This is the control buffer. It is free to use for every
     * layer. Please put your private variables there. If you
     * want to keep them across layers you have to do a skb_clone()
     * first. This is owned by whoever has the skb queued ATM.
     */
    char            cb[48] __aligned(8);------------------------------------这个可以看很多private的处理

    unsigned long        _skb_refdst;
#ifdef CONFIG_XFRM
    struct    sec_path    *sp;
#endif
    unsigned int        len,
                data_len;
    __u16            mac_len,
                hdr_len;
    union {
        __wsum        csum;
        struct {
            __u16    csum_start;
            __u16    csum_offset;
        };
    };
    __u32            priority;
    kmemcheck_bitfield_begin(flags1);
    __u8            RH_KABI_RENAME(local_df, ignore_df):1,
                cloned:1,
                ip_summed:2,
                nohdr:1,
                nfctinfo:3;
    __u8            pkt_type:3,
                fclone:2,
                ipvs_property:1,
                peeked:1,
                nf_trace:1;
    kmemcheck_bitfield_end(flags1);
    __be16            protocol;

    void            (*destructor)(struct sk_buff *skb);
#if defined(CONFIG_NF_CONNTRACK) || defined(CONFIG_NF_CONNTRACK_MODULE)
    struct nf_conntrack    *nfct;
#endif
#if IS_ENABLED(CONFIG_BRIDGE_NETFILTER)
    struct nf_bridge_info    *nf_bridge;
#endif

    /* fields enclosed in headers_start/headers_end are copied
     * using a single memcpy() in __copy_skb_header()
     */
    /* private: */
    RH_KABI_EXTEND(__u32    headers_start[0])
    /* public: */

    int            skb_iif;

    RH_KABI_REPLACE(__u32    rxhash,
            __u32    hash)

    __be16            vlan_proto;
    __u16            vlan_tci;

#ifdef CONFIG_NET_SCHED
    __u16            tc_index;    /* traffic control index */
#ifdef CONFIG_NET_CLS_ACT
    __u16            tc_verd;    /* traffic control verdict */
#endif
#endif

    __u16            queue_mapping;
    kmemcheck_bitfield_begin(flags2);
#ifdef CONFIG_IPV6_NDISC_NODETYPE
    __u8            ndisc_nodetype:2;
#endif
    __u8            pfmemalloc:1;
    __u8            ooo_okay:1;
    __u8            RH_KABI_RENAME(l4_rxhash, l4_hash):1;
    __u8            wifi_acked_valid:1;
    __u8            wifi_acked:1;
    __u8            no_fcs:1;
    __u8            head_frag:1;
    /* Indicates the inner headers are valid in the skbuff. */
    __u8            encapsulation:1;
    RH_KABI_EXTEND(__u8            encap_hdr_csum:1)-----------------------这个使用在我之前一篇博客中有描述。
    RH_KABI_EXTEND(__u8            csum_valid:1)
    RH_KABI_EXTEND(__u8            csum_complete_sw:1)
    RH_KABI_EXTEND(__u8            xmit_more:1)
    RH_KABI_EXTEND(__u8            inner_protocol_type:1)
    RH_KABI_EXTEND(__u8            remcsum_offload:1)
    /* 0/2 bit hole (depending on ndisc_nodetype presence) */
    kmemcheck_bitfield_end(flags2);

#if defined CONFIG_NET_DMA_RH_KABI || defined CONFIG_NET_RX_BUSY_POLL || defined CONFIG_XPS
    union {
        unsigned int    napi_id;
        RH_KABI_EXTEND(unsigned int    sender_cpu)
        RH_KABI_DEPRECATE(dma_cookie_t,    dma_cookie)
    };
#endif
#ifdef CONFIG_NETWORK_SECMARK
    __u32            secmark;
#endif
    union {
        __u32        mark;
        __u32        dropcount;
        __u32        reserved_tailroom;
    };

#ifdef __GENKSYMS__
    __be16            inner_protocol;
#else
    union {
        __be16        inner_protocol;
        __u8        inner_ipproto;
    };
#endif

    __u16            inner_transport_header;
    __u16            inner_network_header;
    __u16            inner_mac_header;
    __u16            transport_header;
    __u16            network_header;
    __u16            mac_header;

    RH_KABI_EXTEND(kmemcheck_bitfield_begin(flags3))
    RH_KABI_EXTEND(__u8    csum_level:2)
    RH_KABI_EXTEND(__u8    rh_csum_pad:1)
    RH_KABI_EXTEND(__u8    csum_bad:1)
    RH_KABI_EXTEND(__u8    offload_fwd_mark:1)
    RH_KABI_EXTEND(__u8    sw_hash:1)
    RH_KABI_EXTEND(__u8     csum_not_inet:1)
    RH_KABI_EXTEND(__u8    dst_pending_confirm:1)
    /* 8 bit hole */
    RH_KABI_EXTEND(kmemcheck_bitfield_end(flags3))

    /* private: */
    RH_KABI_EXTEND(__u32    headers_end[0])
    /* public: */

    /* RHEL SPECIFIC
     *
     * The following padding has been inserted before ABI freeze to
     * allow extending the structure while preserve ABI. Feel free
     * to replace reserved slots with required structure field
     * additions of your backport, eventually moving the replaced slot
     * before headers_end, if it need to be copied by __copy_skb_header()
     */
    u32            rh_reserved1;
    u32            rh_reserved2;
    u32            rh_reserved3;
    u32            rh_reserved4;

    /* These elements must be at the end, see alloc_skb() for details.  */
    sk_buff_data_t        tail;
    sk_buff_data_t        end;
    unsigned char        *head,
                *data;
    unsigned int        truesize;
    atomic_t        users;
};