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

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