Physical RAM Post: 302621697

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Operating Systems Linux Red Hat Physical RAM Post 302621697 by sds9985 on Tuesday 10th of April 2012 11:35:37 PM

04-11-2012

Registered User

An active RHEL system should be using almost all of the free physical memory for cache and buffers. Once you start doing application I/O, you'll see the memory get "used" by the OS quickly. Remember, the memory "used" for cache/buffers is actually free and the kernel can reclaim it very quickly if memory demand for processes increases. The "free" command shows you the difference between "used" memory with and without including the cache/buffers.

Older versions of Linux did have a penalty for very large memory because the algorithms used to manage memory pages were primitive. Many of those problems were addressed in later RHEL 4 releases and by the time we got to RHEL 5 and 6, those issues have been completely resolved. Many of our servers run 256 or 512GB of RAM. For a BL460c with maybe 8 cores, 32GB seems to me to be about right. If it's a BL460cG6 with 16 cores, 32GB seems small. It all depends on what applications or databases you're running on it.

Here's an example from a mid range system with 48 cores:

Code:

# free -g
           total       used       free     shared    buffers     cached
Mem:           251        250          0          0          0        226
-/+ buffers/cache:         24        226
Swap:          294         20        273

At first glance it looks like this system has no free memory. But the actual memory used by processes is actually only 24GB - the other 226GB is cache/buffers.

With very large amounts of RAM on certain hardware you can encounter NUMA issues, but as a general rule, you can never have too much memory. RHEL will find a way to use it.

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mdbfontsize

mdbFontSize(5)							 The m17n Library						    mdbFontSize(5)

NAME

       mdbFontSize - Font Size

DESCRIPTION

       In some case, a font contains incorrect information about its size (typically in the case of a hacked TrueType font), which results in a
       bad text layout when such a font is used in combination with the other fonts. To overcome this problem, the m17n library loads information
       about font-size adjustment from the m17n database by the tags <font, resize>. The data is loaded as a plist of this format.

       FONT-SIZE-ADJUSTMENT ::= PER-FONT *

       PER-FONT ::= '(' FONT-SPEC ADJUST-RATIO ')'

       FONT-SPEC ::=
	   '(' [ FOUNDRY FAMILY
	      [ WEIGHT [ STYLE [ STRETCH [ ADSTYLE ]]]]]
	    REGISTRY ')'

       ADJUST-RATIO ::= INTEGER

       FONT-SPEC is to specify properties of a font. FOUNDRY to REGISTRY are symbols corresponding to Mfoundry to Mregistry property of a font.
       See m17nFont for the meaning of each property.

       ADJUST-RATIO is an integer number specifying by percentage how much the font-size must be adjusted. For instance, this PER-FONT:

	   ((devanagari-cdac) 150)

       instructs the font handler of the m17n library to open a font of 1.5 times bigger than a requested size on opening a font whose registry is
       'devanagari-cdac'.

COPYRIGHT

       Copyright (C) 2001 Information-technology Promotion Agency (IPA)
       Copyright (C) 2001-2011 National Institute of Advanced Industrial Science and Technology (AIST)
       Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License
       <http://www.gnu.org/licenses/fdl.html>.

Version 1.6.2							    12 Jan 2011 						    mdbFontSize(5)

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