Re: [PATCH net 2/2] macvtap: limit head length of skb allocated
On 11/13/2013 01:45 AM, Greg Rose wrote: > On Tue, 12 Nov 2013 18:02:57 +0800 > Jason Wang wrote: > >> We currently use hdr_len as a hint of head length which is advertised >> by guest. But when guest advertise a very big value, it can lead to >> an 64K+ allocating of kmalloc() which has a very high possibility of >> failure when host memory is fragmented or under heavy stress. The >> huge hdr_len also reduce the effect of zerocopy or even disable if a >> gso skb is linearized in guest. >> >> To solves those issues, this patch introduces an upper limit >> (PAGE_SIZE) of the head, which guarantees an order 0 allocation each >> time. >> >> Cc: Stefan Hajnoczi >> Cc: Michael S. Tsirkin >> Signed-off-by: Jason Wang >> --- >> The patch was needed for stable. >> --- >> drivers/net/macvtap.c | 5 + >> 1 file changed, 5 insertions(+) >> >> diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c >> index 9dccb1e..7ee6f9d 100644 >> --- a/drivers/net/macvtap.c >> +++ b/drivers/net/macvtap.c >> @@ -523,6 +523,11 @@ static inline struct sk_buff >> *macvtap_alloc_skb(struct sock *sk, size_t prepad, int noblock, int >> *err) { >> struct sk_buff *skb; >> +int good_linear = SKB_MAX_HEAD(prepad); >> + >> +/* Don't use huge linear part */ >> +if (linear > good_linear) >> +linear = good_linear; >> >> /* Under a page? Don't bother with paged skb. */ >> if (prepad + len < PAGE_SIZE || !linear) > I see no problem with this or the tuntap patch except that in both > cases kernel coding style would prefer that you align the local > variable declarations in a reverse pyramid, longest at the beginning, > shortest at the end. > > - Greg Sure, will do it in V2. Thanks > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majord...@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH net 2/2] macvtap: limit head length of skb allocated
On Tue, 12 Nov 2013 18:02:57 +0800 Jason Wang wrote: > We currently use hdr_len as a hint of head length which is advertised > by guest. But when guest advertise a very big value, it can lead to > an 64K+ allocating of kmalloc() which has a very high possibility of > failure when host memory is fragmented or under heavy stress. The > huge hdr_len also reduce the effect of zerocopy or even disable if a > gso skb is linearized in guest. > > To solves those issues, this patch introduces an upper limit > (PAGE_SIZE) of the head, which guarantees an order 0 allocation each > time. > > Cc: Stefan Hajnoczi > Cc: Michael S. Tsirkin > Signed-off-by: Jason Wang > --- > The patch was needed for stable. > --- > drivers/net/macvtap.c | 5 + > 1 file changed, 5 insertions(+) > > diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c > index 9dccb1e..7ee6f9d 100644 > --- a/drivers/net/macvtap.c > +++ b/drivers/net/macvtap.c > @@ -523,6 +523,11 @@ static inline struct sk_buff > *macvtap_alloc_skb(struct sock *sk, size_t prepad, int noblock, int > *err) { > struct sk_buff *skb; > + int good_linear = SKB_MAX_HEAD(prepad); > + > + /* Don't use huge linear part */ > + if (linear > good_linear) > + linear = good_linear; > > /* Under a page? Don't bother with paged skb. */ > if (prepad + len < PAGE_SIZE || !linear) I see no problem with this or the tuntap patch except that in both cases kernel coding style would prefer that you align the local variable declarations in a reverse pyramid, longest at the beginning, shortest at the end. - Greg -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH net 2/2] macvtap: limit head length of skb allocated
On Tue, Nov 12, 2013 at 06:02:57PM +0800, Jason Wang wrote: > We currently use hdr_len as a hint of head length which is advertised by > guest. But when guest advertise a very big value, it can lead to an 64K+ > allocating of kmalloc() which has a very high possibility of failure when host > memory is fragmented or under heavy stress. The huge hdr_len also reduce the > effect of zerocopy or even disable if a gso skb is linearized in guest. > > To solves those issues, this patch introduces an upper limit (PAGE_SIZE) of > the > head, which guarantees an order 0 allocation each time. > > Cc: Stefan Hajnoczi > Cc: Michael S. Tsirkin > Signed-off-by: Jason Wang Acked-by: Michael S. Tsirkin > --- > The patch was needed for stable. > --- > drivers/net/macvtap.c | 5 + > 1 file changed, 5 insertions(+) > > diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c > index 9dccb1e..7ee6f9d 100644 > --- a/drivers/net/macvtap.c > +++ b/drivers/net/macvtap.c > @@ -523,6 +523,11 @@ static inline struct sk_buff *macvtap_alloc_skb(struct > sock *sk, size_t prepad, > int noblock, int *err) > { > struct sk_buff *skb; > + int good_linear = SKB_MAX_HEAD(prepad); > + > + /* Don't use huge linear part */ > + if (linear > good_linear) > + linear = good_linear; > > /* Under a page? Don't bother with paged skb. */ > if (prepad + len < PAGE_SIZE || !linear) > -- > 1.8.3.2 > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majord...@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/