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
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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
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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
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> Please read the FAQ at http://www.tux.org/lkml/
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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 stefa...@redhat.com
Cc: Michael S. Tsirkin m...@redhat.com
Signed-off-by: Jason Wang jasow...@redhat.com
Acked-by: Michael S. Tsirkin m...@redhat.com
---
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
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Re: [PATCH net 2/2] macvtap: limit head length of skb allocated
On Tue, 12 Nov 2013 18:02:57 +0800
Jason Wang jasow...@redhat.com 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 stefa...@redhat.com
Cc: Michael S. Tsirkin m...@redhat.com
Signed-off-by: Jason Wang jasow...@redhat.com
---
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 11/13/2013 01:45 AM, Greg Rose wrote:
On Tue, 12 Nov 2013 18:02:57 +0800
Jason Wang jasow...@redhat.com 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 stefa...@redhat.com
Cc: Michael S. Tsirkin m...@redhat.com
Signed-off-by: Jason Wang jasow...@redhat.com
---
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
--
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the body of a message to majord...@vger.kernel.org
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Please read the FAQ at http://www.tux.org/lkml/
--
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