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    SubjectRe: [PATCH 10/17] netvm: Allow skb allocation to use PFMEMALLOC reserves
    On Thu, Jun 21, 2012 at 06:30:29PM +0200, Sebastian Andrzej Siewior wrote:
    > > diff --git a/net/core/skbuff.c b/net/core/skbuff.c
    > > index 1d6ecc8..9a58dcc 100644
    > > --- a/net/core/skbuff.c
    > > +++ b/net/core/skbuff.c
    > > @@ -167,14 +206,19 @@ static void skb_under_panic(struct sk_buff *skb, int sz, void *here)
    > > * %GFP_ATOMIC.
    > > */
    > > struct sk_buff *__alloc_skb(unsigned int size, gfp_t gfp_mask,
    > > - int fclone, int node)
    > > + int flags, int node)
    > > {
    > > struct kmem_cache *cache;
    > > struct skb_shared_info *shinfo;
    > > struct sk_buff *skb;
    > > u8 *data;
    > > + bool pfmemalloc;
    > >
    > > - cache = fclone ? skbuff_fclone_cache : skbuff_head_cache;
    > > + cache = (flags & SKB_ALLOC_FCLONE)
    > > + ? skbuff_fclone_cache : skbuff_head_cache;
    > > +
    > > + if (sk_memalloc_socks() && (flags & SKB_ALLOC_RX))
    > > + gfp_mask |= __GFP_MEMALLOC;
    > >
    > > /* Get the HEAD */
    > > skb = kmem_cache_alloc_node(cache, gfp_mask & ~__GFP_DMA, node);
    >
    > This is mostly used by nic to refil their RX skb pool. You add the
    > __GFP_MEMALLOC to the allocation to rise the change of a successfull refill
    > for the swap case.
    > A few drivers use build_skb() to create the skb. __netdev_alloc_skb()
    > shouldn't be affected since the allocation happens with GFP_ATOMIC. Looking at
    > TG3 it uses build_skb() and get_pages() / kmalloc(). Shouldn't this be some
    > considered?
    >

    While TG3 is not exactly as you describe after rebasing build_skb should
    make a similar check to __alloc_skb. As it is always used for RX allocation
    from the skbuff_head_cache cache the following should be suitable. Thanks.

    diff --git a/net/core/skbuff.c b/net/core/skbuff.c
    index 9832001..063830c 100644
    --- a/net/core/skbuff.c
    +++ b/net/core/skbuff.c
    @@ -310,8 +310,12 @@ struct sk_buff *build_skb(void *data, unsigned int frag_size)
    struct skb_shared_info *shinfo;
    struct sk_buff *skb;
    unsigned int size = frag_size ? : ksize(data);
    + gfp_t gfp_mask = GFP_ATOMIC;

    - skb = kmem_cache_alloc(skbuff_head_cache, GFP_ATOMIC);
    + if (sk_memalloc_socks())
    + gfp_mask |= __GFP_MEMALLOC;
    +
    + skb = kmem_cache_alloc(skbuff_head_cache, gfp_mask);
    if (!skb)
    return NULL;


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