Re: [Qemu-devel] [PATCH v3] net: Allocating Large sized arrays to heap

[Pooja Dhannawat <dhannawatpooja1@gmail.com>]

[-- Attachment #1: Type: text/plain, Size: 1507 bytes --]

On Thu, Mar 17, 2016 at 8:23 PM, Stefan Hajnoczi <stefanha@gmail.com> wrote:

> On Tue, Mar 15, 2016 at 11:55:13PM +0530, Pooja Dhannawat wrote:
> > nc_sendv_compat has a huge stack usage of 69680 bytes approx.
> > Moving large arrays to heap to reduce stack usage.
> >
> > Signed-off-by: Pooja Dhannawat <dhannawatpooja1@gmail.com>
> > ---
> >  net/net.c | 14 ++++++++++----
> >  1 file changed, 10 insertions(+), 4 deletions(-)
> >
> > diff --git a/net/net.c b/net/net.c
> > index b0c832e..f03c571 100644
> > --- a/net/net.c
> > +++ b/net/net.c
> > @@ -709,23 +709,29 @@ ssize_t qemu_send_packet_raw(NetClientState *nc,
> const uint8_t *buf, int size)
> >  static ssize_t nc_sendv_compat(NetClientState *nc, const struct iovec
> *iov,
> >                                 int iovcnt, unsigned flags)
> >  {
> > -    uint8_t buf[NET_BUFSIZE];
> > +    uint8_t *buf;
> >      uint8_t *buffer;
> >      size_t offset;
> > +    ssize_t ret;
> > +
> > +    buf = g_new(uint8_t, NET_BUFSIZE);
>
> The linear buffer is only needed when iovcnt > 1.  I suggest the
> following instead:
>
> uint8_t *buf = NULL;
>
> if (iovcnt == 1) {
>     buffer = iov[0].iov_base;
>     offset = iov[0].iov_len;
> } else {
>     buf = g_new(uint8_t, NET_BUFSIZE);
>     buffer = buf;
>     offset = iov_to_buf(iov, iovcnt, 0, buf, NET_BUFSIZE);
> }
>
> This way the allocation is only made when we actually need to linearize
> the buffer.
>

Thanks Stefan for pointing out this one :)  I will make desired changes and
push patch.

[-- Attachment #2: Type: text/html, Size: 2192 bytes --]