Messages in this thread | | | Date | Mon, 16 Apr 2012 16:23:59 +0800 | From | Jason Wang <> | Subject | Re: [PATCH 2/6] macvtap: zerocopy: fix truesize underestimation |
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On 04/16/2012 03:14 PM, Michael S. Tsirkin wrote: > On Mon, Apr 16, 2012 at 02:07:59PM +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@redhat.com> > I'm not sure this is right: the skb does *not* consume the > whole page, userspace uses the rest of the page > for other skbs. So we'll end up accounting for the > same page twice. > Eric, what's the right thing to do here in your opinion?
Or at very least, we need to do this in skb_copy_ubufs() as it allocate whole new pages. >> --- >> 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; >> 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); > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/
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