Re: [libvirt] [PATCH 1/2] rpc: Switch to dynamically allocated message buffer

On 03.05.2012 10:01, Daniel P. Berrange wrote: > On Wed, May 02, 2012 at 01:52:27PM -0600, Eric Blake wrote: >> On 04/27/2012 07:22 AM, Michal Privoznik wrote: >>> Currently, we are allocating buffer for RPC messages statically. >>> This is not such pain when RPC limits are small. However, if we want >>> ever to increase those limits, we need to allocate buffer dynamically, >>> based on RPC message len (= the first 4 bytes). Therefore we will >>> decrease our mem usage in most cases and still be flexible enough in >>> corner cases. >>> --- >>> src/rpc/virnetclient.c | 16 ++- >>> src/rpc/virnetmessage.c | 12 ++- >>> src/rpc/virnetmessage.h | 6 +- >>> src/rpc/virnetserverclient.c | 20 ++- >>> tests/virnetmessagetest.c | 393 +++++++++++++++++++++++------------------- >>> 5 files changed, 264 insertions(+), 183 deletions(-) >> >> I haven't looked closely at this, but I do have a generic question: >> >> Are you malloc'ing and free'ing the buffer for each rpc on every call, >> or are you tracking a pool of buffers and only alloc'ing when needed? >> Furthermore, can you use the stack or a statically allocated array to >> receive short messages, saving alloc only for the long messages? I'm >> worried about performance if we malloc on every single RPC call. > > To be honest I'm not convinced malloc() would be a big factor in the > speed of the RPC calls. That said you could optimize it using the > VIR_ALLOC_VAR to allocate the virNetMessage struct + the buffer > in one go. ALlocate all messages with 256kb initially and then you > can relloc larger only if needed, and re-alloc back to 256 kb when > done. > > > Daniel Okay, point taken. Although I'd rather avoid allocating virNetMessage struct and buffer at once. It would complicate the code again, because the client side code has this struct _virNetClient; which already contains virNetMessage. However, if I'd need to re-alloc, I'd need to realloc whole message (!) therefore change the member to virNetMessagePtr. This implies too many changes.