Re: [V2 PATCH 2/9] macvtap: zerocopy: fix truesize underestimation

[Jason Wang]

On 05/16/2012 01:26 AM, Shirley Ma wrote:
> On Wed, 2012-05-02 at 11:41 +0800, Jason Wang wrote:
> > As the skb fragment were pinned/built from user pages, we should
> > account the page instead of length for truesize.
> >
> > Signed-off-by: Jason Wang<jasowang@xxxxxxxxxx>
> > ---
> >   drivers/net/macvtap.c |    6 ++++--
> >   1 files changed, 4 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
> > index bd4a70d..7cb2684 100644
> > --- a/drivers/net/macvtap.c
> > +++ b/drivers/net/macvtap.c
> > @@ -519,6 +519,7 @@ static int zerocopy_sg_from_iovec(struct sk_buff
> > *skb, const struct iovec *from,
> >                  struct page *page[MAX_SKB_FRAGS];
> >                  int num_pages;
> >                  unsigned long base;
> > +               unsigned long truesize;
> >
> >                  len = from->iov_len - offset;
> >                  if (!len) {
> > @@ -533,10 +534,11 @@ static int zerocopy_sg_from_iovec(struct sk_buff
> > *skb, const struct iovec *from,
> >                      (num_pages>  MAX_SKB_FRAGS -
> > skb_shinfo(skb)->nr_frags))
> >                          /* put_page is in skb free */
> >                          return -EFAULT;
> > +               truesize = size * PAGE_SIZE;
> Here should be truesize = size * PAGE_SIZE - offset, right?

We get the whole user page, so need to account them all. Also this is 
aligned with skb_copy_ubufs().
> >                  skb->data_len += len;
> >                  skb->len += len;
> > -               skb->truesize += len;
> > -               atomic_add(len,&skb->sk->sk_wmem_alloc);
> > +               skb->truesize += truesize;
> > +               atomic_add(truesize,&skb->sk->sk_wmem_alloc);
> >                  while (len) {
> >                          int off = base&  ~PAGE_MASK;
> >                          int size = min_t(int, len, PAGE_SIZE - off);

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