High memory and low memory explanation.When running <span style="font-family: courier new,courier,monospace;">show module status </span>command from CLI or <em>cat<span style="font-family: courier new,courier,monospace;"> /proc/meminfo </span></em>command on the module, the output lists values for High and Low memory (output cropped):<br /><div style="margin-left: 40px;"> </div> <div style="margin-left: 40px;"> <span style=""><span style="font-family: courier new,courier,monospace;">total: used: free: shared: buffers: cached: <br /> Mem: 1049051136 765775872 283275264 0 158441472 376979456 <br /> Swap: 1036115968 0 1036115968 <br /> MemTotal: 1024464 kB <br /> MemFree: 276636 kB <br /> MemShared: 0 kB <br /> Buffers: 154728 kB <br /> Cached: 368144 kB </span><br /> <span style="color: #ff0000;"><span style="font-family: courier new,courier,monospace;">... <br /> HighTotal: 131072 kB <br /> HighFree: 3064 kB <br /> LowTotal: 893392 kB <br /> LowFree: 273572 kB</span></span></span><br /> </div> <div> This article attempts to clarify Low and High memory details.</div>
On a 32-bit Linux based operating system, CPU can address maximum of 4GB of memory. The memory is further divided in Low memory (or Normal memory), which is directly mapped to kernel's part of the address space and High memory, which has no direct kernel mapping. In other words:<br /><br /><div> - The kernel itself (including its active modules, e.g. Check Point kernel modules) can only make use of LOW memory.</div> <div> - User processes on the system (anything that is not kernel itself) can potentially make use of LOW and HIGH memory.<br /> <br /> Because of this Low memory limitation OoM (Out of Memory killer) can be invoked even if there is a plenty of free memory in total. This situation occurs when the Low memory is exhausted and kernel needs to allocate more memory. However, it is a highly unusual situation to have a lot of high memory free but run out of low memory. More common is to see high AND low memory heading towards zero.</div> <br />High memory normally starts above 896MB. However on a Blue Coat X-Series chassis, the thresholds are different.
<div> Please note that on a 64-bit OS, because there is more than enough virtual memory address space, Low memory equals Total memory. When running <span style="">show module status </span>command from CLI, Low and High memory values are not present.<br /> <br /> <div style="margin-left: 40px;"> <span style="font-family: courier new,courier,monospace;"> Slot 14:</span></div> <div style="margin-left: 40px;"> <span style="font-family: courier new,courier,monospace;"> SDRAM 1 Size 1048576(KB)</span></div> <div style="margin-left: 40px;"> <span style="font-family: courier new,courier,monospace;"> SDRAM 2 Size 1048576(KB)</span></div> <div style="margin-left: 40px;"> <span style="font-family: courier new,courier,monospace;"> SDRAM 3 Size 1048576(KB)</span></div> <div style="margin-left: 40px;"> <span style="font-family: courier new,courier,monospace;"> SDRAM 4 Size 1048576(KB)</span></div> <div style="margin-left: 40px;"> <span style="font-family: courier new,courier,monospace;"> SDRAM Total Size 4194304(KB)</span></div> <div style="margin-left: 40px;"> <span style="font-family: courier new,courier,monospace;"> Reserved Memory 602536(KB)</span></div> <div style="margin-left: 40px;"> <span style="font-family: courier new,courier,monospace;"> Total Memory 3591768(KB)</span></div> <div style="margin-left: 40px;"> <span style="font-family: courier new,courier,monospace;"> Used Memory 453144(KB)</span></div> <div style="margin-left: 40px;"> <span style="font-family: courier new,courier,monospace;"> Free Memory 3138624(KB)</span></div> <div style="margin-left: 40px;"> <span style="font-family: courier new,courier,monospace;"> Shared Memory 0(KB)</span></div> <div style="margin-left: 40px;"> <span style="font-family: courier new,courier,monospace;"> Buffers Memory 139340(KB)</span></div> <div style="margin-left: 40px;"> <span style="font-family: courier new,courier,monospace;"> Cached Memory 187200(KB)</span></div> <div style="margin-left: 40px;"> <span style="font-family: courier new,courier,monospace;"> Memory Utilization 3.52%</span></div> <div> </div> <br /> When running <em>cat<span style=""> /proc/meminfo </span></em>command on the module, HighTotal and HighFree will always be zero:<br /> <div> </div> <div style="margin-left: 40px;"> <span style="font-family: courier new,courier,monospace;"># cat /proc/meminfo</span></div> <div style="margin-left: 40px;"> <span style="font-family: courier new,courier,monospace;">MemTotal: 3591768 kB</span></div> <div style="margin-left: 40px;"> <span style="font-family: courier new,courier,monospace;">MemFree: 135968 kB</span></div> <div style="margin-left: 40px;"> <span style="font-family: courier new,courier,monospace;">Buffers: 378312 kB</span></div> <div style="margin-left: 40px;"> <span style="font-family: courier new,courier,monospace;">Cached: 1754432 kB</span></div> <div style="margin-left: 40px;"> <span style="font-family: courier new,courier,monospace;">SwapCached: 68 kB</span></div> <div style="margin-left: 40px;"> <span style="font-family: courier new,courier,monospace;">Active: 965532 kB</span></div> <div style="margin-left: 40px;"> <span style="font-family: courier new,courier,monospace;">Inactive: 2080476 kB</span></div> <div style="margin-left: 40px;"> <span style="color: #ff0000;"><span style="font-family: courier new,courier,monospace;">HighTotal: 0 kB</span></span></div> <div style="margin-left: 40px;"> <span style="color: #ff0000;"><span style="font-family: courier new,courier,monospace;">HighFree: 0 kB</span></span></div> <div> </div> </div> <br /><h3>Workaround</h3>N/A