manuals: add minimum RAM requirements

Measured by generating a "core-image-sato" image for a "qemux86-64"
machine from an Ubuntu 22.04 VM with 4 cores.

Less memory was not enough and caused Out of Memory failures.

(From yocto-docs rev: a05f87929eed43cef673a8c2581899a8c9ccf462)

Signed-off-by: Michael Opdenacker <michael.opdenacker@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

documentation/brief-yoctoprojectqs/index.rst

@@ -44,6 +44,10 @@ following requirements:
    much more will help to run multiple builds and increase
    performance by reusing build artifacts.
 
+-  At least &MIN_RAM; Gbytes of RAM, though a modern modern build host with as
+   much RAM and as many CPU cores as possible is strongly recommended to
+   maximize build performance.
+
 -  Runs a supported Linux distribution (i.e. recent releases of Fedora,
    openSUSE, CentOS, Debian, or Ubuntu). For a list of Linux
    distributions that support the Yocto Project, see the

documentation/poky.yaml.in

@@ -45,3 +45,5 @@ MIN_MAKE_VERSION : "4.0"
 MIN_DISK_SPACE : "90"
 # Disk space (Gbytes) needed to generate qemux86-64 core-image-sato on Ubuntu 22.04 (x86-64) with "rm_work", rounded up from 38
 MIN_DISK_SPACE_RM_WORK : "40"
+# RAM (Gbytes) needed to generate qemux86-64 core-image-sato on Ubuntu 22.04 (x86-64) on a 4 core system
+MIN_RAM : "8"

documentation/ref-manual/system-requirements.rst

@@ -42,6 +42,14 @@ to run multiple builds and to cache build artifacts, improving build efficiency.
 If you have a shortage of disk space, see the ":doc:`/dev-manual/disk-space`"
 section of the Development Tasks Manual.
 
+Minimum System RAM
+==================
+
+You will manage to build an image such as ``core-image-sato`` for the
+``qemux86-64`` machine with as little as &MIN_RAM; Gbytes of RAM on an old
+system with 4 CPU cores, but your builds will be much faster on a system with
+as much RAM and as many CPU cores as possible.
+
 Supported Linux Distributions
 =============================