How to install a patch ?

Hi,

I have a patch download, pg_prewarm_v2.patch and according to the document, I need to apply pg_prewarm patch on my PG source installation :
1. Untar location of PG source : /usr/local/src/postgresql-9.1.3
2. PG installation locatin : /usr/local/pgsql91
3. All downloads Location : /usr/local/src

I installed the postgres using rpm and unable to find the source directory.

Have tried the following but not working :
patch -p1 -d /var/lib/pgsql < pg_prewarm_v2.patch

Anyone, please guide ?

Regards,
Eye Gee