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3.2. Linux Performance Tools: CPU and MemoryHere begins our discussion of performance tools that enable you to extract the memory performance information described previously. 3.2.1. vmstat (Virtual Memory Statistics) IIAs you have seen before, vmstat can provide information about many different performance aspects of a system—although its primary purpose, as shown next, is to provide information about virtual memory system performance. In addition to the CPU performance statistics described in the previous chapter, it can also tell you the following:
As you can see, vmstat provides (via the statistics it displays) a wealth of information about the health and performance of the system in a single line of text. 3.2.1.1 System-Wide Memory-Related OptionsIn addition to the CPU statistics vmstat can provide, you can invoke vmstat with the following command-line options when investigating memory statistics: vmstat [-a] [-s] [-m] As before, you can run vmstat in two modes: sample mode and average mode. The added command-line options enable you to get the performance statistics about how the Linux kernel is using memory. Table 3-1 describes the options that vmstat accepts. Table 3-2 provides a list of the memory statistics that vmstat can provide. As with the CPU statistics, when run in normal mode, the first line that vmstat provides is the average values for all the rate statistics (so and si) and the instantaneous value for all the numeric statistics (swpd, free, buff, cache, active, and inactive). vmstat provides a good overview of the current state of the virtual memory system for a given machine. Although it does not provide a complete and detailed list of every Linux memory performance statistic available, it does provide a compact output that can indicate how the system memory is being used overall. 3.2.1.2 Example UsageIn Listing 3.2, as you saw in the previous chapter, if vmstat is invoked without any command-line options, it displays average values for performance statistics since system boot (si and so), and it shows the instantaneous values for the rest of them (swpd, free, buff, and cache). In this case, we can see that the system has about 500MB of memory that has been swapped to disk. ~14MB of the system memory is free. ~4MB is used for buffers that contain data that has yet to be flushed to disk. ~627MB is used for the disk cache that contains data that has been read off the disk in the past. Listing 3.2.bash-2.05b$ vmstat procs -----------memory---------- ---swap-- -----io---- --system-- ----cpu---- r b swpd free buff cache si so bi bo in cs us sy id wa 0 0 511012 14840 4412 642072 33 31 204 247 1110 1548 8 5 73 14 In Listing 3.3, we ask vmstat to display information about the number of active and inactive pages. The amount of inactive pages indicates how much of the memory could be swapped to disk and how much is currently being used. In this case, we can see that 1310MB of memory is active, and only 78MB is considered inactive. This machine has a large amount of memory, and much of it is being actively used. Listing 3.3.bash-2.05b$ vmstat -a procs -----------memory---------- ---swap-- -----io---- --system-- ----cpu---- r b swpd free inact active si so bi bo in cs us sy id wa 2 1 514004 5640 79816 1341208 33 31 204 247 1111 1548 8 5 73 14 Next, in Listing 3.4, we look at a different system, one that is actively swapping data in and out of memory. The si column indicates that swap data has been read in at a rate of 480KB, 832KB, 764KB, 344KB, and 512KB during each of those sample periods. The so column indicates that memory data has been written to swap at a rate of 9KB, 0KB, 916KB, 0KB, 1068KB, 444KB, 792KB, during each of the samples. These results could indicate that the system does not have enough memory to handle all the running processes. A simultaneously high swap-in and swap-out rate can occur when a process's memory is being saved to make way for an application that had been previously swapped to disk. This can be disastrous if two running programs both need more memory than the system can provide. For example, if two processes are using a large amount of memory, and both are trying to run simultaneously, each can cause the other's memory to be written to swap. When one of the programs needs a piece of memory, it kicks out one that the other applications needs. When the other application starts to run, it kicks out a piece of memory that the original program was using, and waits until its memory is loaded from the swap. This can cause both applications to grind to a halt while they wait for their memory to be retrieved from swap before they can continue execution. As soon as one makes a little bit of progress, it swaps out memory that the other process was using and causes the other program to slow down. This is called thrashing. When this happens, the system spends most of its time reading memory to and from the swap, and system performance dramatically slows down. In this particular case, the swapping eventually stopped, so most likely the memory that was swapped to disk was not immediately needed by the original process. This means the swap usage was effective, the contents of the memory that was not being used was written to disk, and the memory was then given to the process that needed it. Listing 3.4.[ezolt@localhost book]$ vmstat 1 100 procs -----------memory---------- ---swap-- -----io---- --system-- ----cpu---- r b swpd free buff cache si so bi bo in cs us sy id wa 2 1 131560 2320 8640 53036 1 9 107 69 1137 426 10 7 74 9 0 1 131560 2244 8640 53076 480 0 716 0 1048 207 6 1 0 93 1 2 132476 3424 8592 53272 832 916 1356 916 1259 692 11 4 0 85 1 0 132476 2400 8600 53280 764 0 1040 40 1288 762 14 5 0 81 0 1 133544 2656 8624 53392 344 1068 1096 1068 1217 436 8 3 5 84 0 1 133988 2300 8620 54288 512 444 1796 444 1090 230 5 1 2 92 0 0 134780 3148 8612 53688 0 792 0 792 1040 166 5 1 92 2 0 0 134780 3148 8612 53688 0 0 0 0 1050 158 4 1 95 0 0 0 134780 3148 8612 53688 0 0 0 0 1148 451 7 2 91 0 0 0 134780 3148 8620 53680 0 0 0 12 1196 477 8 2 78 12 .... As shown in Listing 3.5, as you saw in the previous chapter, vmstat can show a vast array of different system statistics. Now as we look at it, we can see some of the same statistics that were present in some of the other output modes, such as active, inactive, buffer, cache, and used swap. However, it also has a few new statistics, such as total memory, which indicates that this system has a total of 1516MB of memory, and total swap, which indicates that this system has a total of 2048MB of swap. It can be helpful to know the system totals when trying to figure out what percentage of the swap and memory is currently being used. Another interesting statistic is the pages paged in, which indicates the total number of pages that were read from the disk. This statistic includes the pages that are read starting an application and those that the application itself may be using. Listing 3.5.
bash-2.05b$ vmstat -s
1552528 total memory
1546692 used memory
1410448 active memory
11100 inactive memory
5836 free memory
2676 buffer memory
645864 swap cache
2097096 total swap
526280 used swap
1570816 free swap
20293225 non-nice user cpu ticks
18284715 nice user cpu ticks
17687435 system cpu ticks
357314699 idle cpu ticks
67673539 IO-wait cpu ticks
352225 IRQ cpu ticks
4872449 softirq cpu ticks
495248623 pages paged in
600129070 pages paged out
19877382 pages swapped in
18874460 pages swapped out
2702803833 interrupts
3763550322 CPU context switches
1094067854 boot time
20158151 forks
Finally, in Listing 3.6, we see that vmstat can provide information about how the Linux kernel allocates its memory. As previously described, the Linux kernel has a series of "slabs" to hold its dynamic data structures. vmstat displays each of the slabs (Cache), shows how many of the elements are being used (Num), shows how many are allocated (Total), shows the size of each element (Size), and shows the amount of memory in pages (Pages) that the total slab is using. This can be helpful when tracking down exactly how the kernel is using its memory. Listing 3.6.bash-2.05b$ vmstat -m Cache Num Total Size Pages udf_inode_cache 0 0 416 9 fib6_nodes 7 113 32 113 ip6_dst_cache 9 17 224 17 ndisc_cache 1 24 160 24 raw6_sock 0 0 672 6 udp6_sock 0 0 640 6 tcp6_sock 404 441 1120 7 ip_fib_hash 39 202 16 202 ext3_inode_cache 1714 3632 512 8 ... vmstat provides an easy way to extract large amounts of information about the Linux memory subsystem. When combined with the other information provided on the default output screen, it provides a fair picture of the health and resource usage of the system. 3.2.2. top (2.x and 3.x)As discussed in the previous chapter, top presents both system-wide and process-specific performance statistics. By default, top presents a list, in decreasing order, of the top CPU-consuming processes, but it can also be adjusted to sort by the total memory usage, enabling you to track down which process is using the most memory. 3.2.2.1 Memory Performance-Related Optionstop does not have any special command-line options that manipulate its display of memory statistics. It is invoked with the following command line: top However, once running, top enables you to select whether system-wide memory information displays, and whether processes are sorted by memory usage. Sorting by memory consumption proves particularly useful to determine which process is consuming the most memory. Table 3-3 describes the different memory-related output toggles. Table 3-4 describes the memory performance statistics that top can provide for both the entire system and individual processes. top has two different versions, 2.x and 3.x, which have slightly different names for output statistics. Table 3-4 describes the names for both versions. top provides a large amount of memory information about the different running processes. As discussed in later chapters, you can use this information to determine exactly how an application allocates and uses memory. 3.2.2.2 Example UsageListing 3.7 is similar to the example run of top shown in the previous chapter. However, in this example, notice that in the buffers, we have a total amount of 1,024MB of physical memory, of which ~84MB is free. Listing 3.7.
[ezolt@wintermute doc]$ top
top - 15:47:03 up 24 days, 4:32, 15 users, load average: 1.17, 1.19, 1.17
Tasks: 151 total, 1 running, 138 sleeping, 11 stopped, 1 zombie
Cpu(s): 1.2% us, 0.7% sy, 0.0% ni, 93.0% id, 4.9% wa, 0.0% hi, 0.1% si
Mem: 1034320k total, 948336k used, 85984k free, 32840k buffers
Swap: 2040244k total, 276796k used, 1763448k free, 460864k cached
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
26364 root 16 0 405m 71m 321m S 4.0 7.1 462:25.50 X
17345 ezolt 16 0 176m 73m 98m S 2.6 7.3 1:17.48 soffice.bin
18316 ezolt 16 0 2756 1096 1784 R 0.7 0.1 0:05.54 top
26429 ezolt 16 0 65588 52m 12m S 0.3 5.2 16:16.77 metacity
26510 ezolt 16 0 19728 5660 16m S 0.3 0.5 27:57.87 clock-applet
26737 ezolt 16 0 70224 35m 20m S 0.3 3.5 8:32.28 gnome-terminal
1 root 16 0 2396 448 1316 S 0.0 0.0 0:01.72 init
2 root RT 0 0 0 0 S 0.0 0.0 0:00.88 migration/0
3 root 34 19 0 0 0 S 0.0 0.0 0:00.01 ksoftirqd/0
4 root RT 0 0 0 0 S 0.0 0.0 0:00.35 migration/1
5 root 34 19 0 0 0 S 0.0 0.0 0:00.01 ksoftirqd/1
6 root RT 0 0 0 0 S 0.0 0.0 0:34.20 migration/2
7 root 34 19 0 0 0 S 0.0 0.0 0:00.01 ksoftirqd/2
Again, top can be customized to display only what you are interested in observing. Listing 3.8 shows a highly configured output screen that shows only memory performance statistics. Listing 3.8.
Mem: 1034320k total, 948336k used, 85984k free, 33024k buffers
Swap: 2040244k total, 276796k used, 1763448k free, 460680k cached
VIRT RES SHR %MEM SWAP CODE DATA nFLT nDRT COMMAND
405m 71m 321m 7.1 333m 1696 403m 4328 0 X
70224 35m 20m 3.5 33m 280 68m 3898 0 gnome-terminal
2756 1104 1784 0.1 1652 52 2704 0 0 top
19728 5660 16m 0.5 13m 44 19m 17 0 clock-applet
2396 448 1316 0.0 1948 36 2360 16 0 init
0 0 0 0.0 0 0 0 0 0 migration/0
0 0 0 0.0 0 0 0 0 0 ksoftirqd/0
0 0 0 0.0 0 0 0 0 0 migration/1
0 0 0 0.0 0 0 0 0 0 ksoftirqd/1
0 0 0 0.0 0 0 0 0 0 migration/2
0 0 0 0.0 0 0 0 0 0 ksoftirqd/2
0 0 0 0.0 0 0 0 0 0 migration/3
top provides a real-time update of memory statistics and a display of which processes are using which types of memory. This information becomes useful as we investigate application memory usage. 3.2.3. procinfo IIAs we've seen before, procinfo provides a view of the system-wide performance characteristics. In addition to the statistics described in the previous chapter, procinfo provides a few memory statistics, similar to vmstat and top, that indicate how the current memory is being used. 3.2.3.1 Memory Performance-Related Optionsprocinfo does not have any options that change the output of the memory statistics displayed and, as a result, is invoked with the following command: procinfo procinfo displays the basic memory system memory statistics, similar to top and vmstat. These are shown in Table 3-5. Much like vmstat or top, procinfo is a low-overhead command that is good to leave running in a console or window on the screen. It gives a good indication of a system's health and performance. 3.2.3.2 Example UsageListing 3.9 is a typical output for procinfo. As you can see, it reports summary information about how the system is using virtual memory. In this case, the system has a total of 312MB of memory; 301MB is in use by the kernel and applications, 11MB is used by system buffers, and 11MB is not used at all. Listing 3.9.
[ezolt@localhost procinfo-18]$ ./procinfo
Linux 2.6.6-1.435.2.3smp (bhcompile@tweety.build.redhat.com) (gcc 3.3.3 20040412 )
#1
1CPU [localhost]
Memory: Total Used Free Shared Buffers
Mem: 320468 308776 11692 0 11604
Swap: 655192 220696 434496
Bootup: Sun Oct 24 10:03:43 2004 Load average: 0.44 0.53 0.51 3/110 32243
user : 0:57:58.92 9.0% page in : 0
nice : 0:02:51.09 0.4% page out: 0
system: 0:20:18.43 3.2% swap in : 0
idle : 8:47:31.54 81.9% swap out: 0
uptime: 10:44:01.94 context : 13368094
irq 0: 38645994 timer irq 7: 2
irq 1: 90516 i8042 irq 8: 1 rtc
irq 2: 0 cascade [4] irq 9: 2
irq 3: 742857 prism2_cs irq 10: 2
irq 4: 6 irq 11: 562551 uhci_hcd, yenta, yen
irq 5: 2 irq 12: 1000803 i8042
irq 6: 8 irq 14: 207681 ide0
procinfo provides information about system performance in a single screen of information. Although it provides a few of the important statistics for memory, vmstat or top is much better suited for investigating system-wide memory usage. 3.2.4. gnome-system-monitor (II)gnome-system-monitor is in many ways a graphical counterpart of top. It enables you to monitor individual process and observe the load on the system based on the graphs that it displays. It also provides rudimentary graphs of CPU and memory usage. 3.2.4.1 Memory Performance-Related Optionsgnome-system-monitor can be invoked from the Gnome menu. (Under Red Hat 9 and higher, this is in System Tools > System Monitor.) However, it can also be invoked using the following command: gnome-system-monitor gnome-system-monitor has no relevant command-line options that affect the memory performance measurements. 3.2.4.2 Example UsageWhen you launch gnome-system-monitor and select the System Monitor tab, you see a window similar to Figure 3-1. This window enables you to glance at the graph and see how much physical memory and swap is currently being used, and how its usage has changed over time. In this case, we see that 969MB of a total of 1,007MB is currently being used. The memory usage has been relatively flat for a while. Figure 3-1.
The graphical view of data provided by gnome-system-monitor can make it easier and faster; however, most of the details, such as how the memory is being used, are missing. 3.2.5. freefree provides an overall view of how your system is using your memory, including the amount of free memory. Although the free command may show that a particular system does not have much free memory, this is not necessarily bad. Instead of letting memory sit unused, the Linux kernel puts it to work as a cache for disk reads and as a buffer for disk writes. This can dramatically increase system performance. Because these cache and buffers can always be discarded and the memory can be used if needed by applications, free shows you the amount of free memory plus or minus these buffers. 3.2.5.1 Memory Performance-Related Optionsfree can be invoked using the following command line: free [-l] [-t] [-s delay ] [-c count ] Table 3-6 describes the parameters that modify the types of statistics that free displays. Much like vmstat, free can periodically display updated memory statistics. free actually displays some of the most complete memory statistics of any of the memory statistic tools. The statistics that it displays are shown in Table 3-7. free provides information about the system-wide memory usage of Linux. It is a fairly complete range of memory statistics. 3.2.5.2 Example UsageCalling free without any command options gives you an overall view of the memory subsystem. As mentioned previously, Linux tries to use all the available memory if possible to cache data and applications. In Listing 3.10, free tells us that we are currently using 234,720 bytes of memory; however, if you ignore the buffers and cache, we are only using 122,772 bytes of memory. The opposite is true of the free column. We currently have 150,428 bytes of memory free; if you also count the buffers and cached memory (which you can, because Linux throws away those buffers if the memory is needed), however, we have 262,376 bytes of memory free. Listing 3.10.
[ezolt@wintermute procps-3.2.0]$ free
total used free shared buffers cached
Mem: 385148 234720 150428 0 8016 103932
-/+ buffers/cache: 122772 262376
Swap: 394080 81756 312324
Although you could just total the columns yourself, the -t flag shown in Listing 3.11 tells you the totals when adding both swap and real memory. In this case, the system had 376MB of physical memory and 384MB of swap. The total amount of memory available on the system is 376MB plus 384MB, or ~760MB. The total amount of free memory was 134MB of physical memory plus 259MB of swap, yielding a total of 393MB of free memory. Listing 3.11.
[ezolt@wintermute procps-3.2.0]$ free -t
total used free shared buffers cached
Mem: 385148 247088 138060 0 9052 115024
-/+ buffers/cache: 123012 262136
Swap: 394080 81756 312324
Total: 779228 328844 450384
Finally, free tells you the amount of high and low memory that the system is using. This is mainly useful on 32-bit machines (such as IA32) with 1GB or more of physical memory. (32-bit machines are the only machines that will have high memory.) Listing 3.12 shows a system with a very small amount of free memory, 6MB in total. It shows a system with 876MB of low memory and 640MB of high memory. This system also has much more cached memory than buffer memory, suggesting that it may be aggressively writing data to disk rather than leaving it in the buffer cache a long time. Listing 3.12.
fas% free -l
total used free shared buffers cached
Mem: 1552528 1546472 6056 0 7544 701408
Low: 897192 892800 4392
High: 655336 653672 1664
-/+ buffers/cache: 837520 715008
Swap: 2097096 566316 1530780
free gives a good idea of how the system memory is being used. It may take a little while to get used to output format, but it contains all the important memory statistics. 3.2.6. slabtopslabtop is similar to top, but instead of displaying information about the CPU and memory usage of the processes in the system, slabtop shows in real-time how the kernel is allocating its various caches and how full they are. Internally, the kernel has a series of caches that are made up of one or more slabs. Each slab consists of a set of one or more objects. These objects can be active (or used) or inactive (unused). slabtop shows you the status of the different slabs. It shows you how full they are and how much memory they are using. 3.2.6.1 Memory Performance-Related Optionsslabtop is invoked using the following command line:
slabtop [--delay n –sort={a | b | c | l | v | n | o | p | s | u}
The command-line options for slabtop are described in Table 3-8. slabtop provides a glimpse into the data structures of the Linux kernel. Each of these slab types is tied closed to the Linux kernel, and a description of each of these slabs is beyond the scope of this book. If a particular slab is using a large amount of kernel memory, reading the Linux kernel source code and searching the Web are two great ways to figure out what these slabs are used for. 3.2.6.2 Example UsageAs shown in Listing 3.13, by default, slabtop fills the entire console and continually updates the statistics every three seconds. In this example, you can see that the size-64 slab has the most objects, only half of which are active. Listing 3.13.[ezolt@wintermute proc]$ slabtop Active / Total Objects (% used) : 185642 / 242415 (76.6%) Active / Total Slabs (% used) : 12586 / 12597 (99.9%) Active / Total Caches (% used) : 88 / 134 (65.7%) Active / Total Size (% used) : 42826.23K / 50334.67K (85.1%) Minimum / Average / Maximum Object : 0.01K / 0.21K / 128.00K OBJS ACTIVE USE OBJ SIZE SLABS OBJ/SLAB CACHE SIZE NAME 66124 34395 52% 0.06K 1084 61 4336K size-64 38700 35699 92% 0.05K 516 75 2064K buffer_head 30992 30046 96% 0.15K 1192 26 4768K dentry_cache 21910 21867 99% 0.27K 1565 14 6260K radix_tree_node 20648 20626 99% 0.50K 2581 8 10324K ext3_inode_cache 11781 7430 63% 0.03K 99 119 396K size-32 9675 8356 86% 0.09K 215 45 860K vm_area_struct 6024 2064 34% 0.62K 1004 6 4016K ntfs_big_inode_cache 4520 3633 80% 0.02K 20 226 80K anon_vma 4515 3891 86% 0.25K 301 15 1204K filp 4464 1648 36% 0.12K 144 31 576K size-128 3010 3010 100% 0.38K 301 10 1204K proc_inode_cache 2344 587 25% 0.50K 293 8 1172K size-512 2250 2204 97% 0.38K 225 10 900K inode_cache 2100 699 33% 0.25K 140 15 560K size-256 1692 1687 99% 0.62K 282 6 1128K nfs_inode_cache 1141 1141 100% 4.00K 1141 1 4564K size-4096 Because the information provided by slabtop is updated periodically, it is a great way to see how the Linux kernel's memory usage changes in response to different workloads. 3.2.7. sar (II)All the advantages of using sar as a CPU performance tool, such as the easy recording of samples, extraction to multiple output formats, and time stamping of each sample, are still present when monitoring memory statistics. sar provides similar information to the other memory statistics tools, such as the current values for the amount of free memory, buffers, cached, and swap amount. However, it also provides the rate at which these value change and provides information about the percentage of physical memory and swap that is currently being consumed. 3.2.7.1 Memory Performance-Related Optionssar can be invoked with the following command line: sar [-B] [-r] [-R] By default, sar displays only CPU performance statistics; so to retrieve any of the memory subsystem statistics, you must use the options described in Table 3-9. sar provides a fairly complete view of the Linux memory subsystem. One advantage that sar provides over other tools is that it shows the rate of change for many of the important values in addition to the absolute values. You can use these values to see exactly how memory usage is changing over time without having to figure out the differences between values at each sample. Table 3-10 shows the memory statistics that sar provides. Although sar misses the high and low memory statistics, it provides nearly every other memory statistic. The fact that it can also record network CPU and disk I/O statistics makes it very powerful. 3.2.7.2 Example UsageListing 3.14 shows sar providing information about the current state of the memory subsystem. From the results, we can see that the amount of memory that the system used varies from 98.87 percent to 99.25 percent of the total memory. Over the course of the observation, the amount of free memory drops from 11MB to 7MB. The percentage of swap that is used hovers around ~11 percent. The system has ~266MB of data cache and about 12MB in buffers that can be written to disk. Listing 3.14.[ezolt@scrffy manuscript]$ sar -r 1 5 Linux 2.6.8-1.521smp (scrffy) 10/25/2004 09:45:30 AM kbmemfree kbmemused %memused kbbuffers kbcached kbswpfree kbswpused Listing 3.15 shows that the system is consuming the free memory at a rate of ~82 pages per second during the first sample. Later, it frees ~16 pages, and then consumes ~20 pages. The number pages of buffers grew only once during the observation, at a rate of 2.02 pages per second. Finally, the pages of cache shrunk by 2.02, but in the end, they expanded by 64.36 pages/second. Listing 3.15.[ezolt@scrffy manuscript]$ sar -R 1 5 Linux 2.6.8-1.521smp (scrffy) 10/25/2004 09:57:22 AM frmpg/s bufpg/s campg/s 09:57:23 AM -81.19 0.00 0.00 09:57:24 AM 8.00 0.00 0.00 09:57:25 AM 0.00 2.02 -2.02 09:57:26 AM 15.84 0.00 0.00 09:57:27 AM -19.80 0.00 64.36 Average: -15.54 0.40 12.55 Listing 3.16 shows that the system wrote ~53 pages of memory to disk during the third sample. The system has a relatively high fault count, which means that memory pages are being allocated and used. Fortunately, none of these are major faults, meaning that the system does not have to go to disk to fulfill the fault. Listing 3.16.[ezolt@scrffy dvi]$ sar -B 1 5 Linux 2.6.8-1.521smp (scrffy) 10/25/2004 09:58:34 AM pgpgin/s pgpgout/s fault/s majflt/s 09:58:35 AM 0.00 0.00 1328.28 0.00 09:58:36 AM 0.00 0.00 782.18 0.00 09:58:37 AM 0.00 53.06 678.57 0.00 09:58:38 AM 0.00 0.00 709.80 0.00 09:58:39 AM 0.00 0.00 717.17 0.00 Average: 0.00 10.42 842.48 0.00 As you can see, sar is a powerful tool that enhances the functionality of the other system memory performance tools by adding the ability to archive, time stamp, and simultaneously collect many different types of statistics. 3.2.8. /proc/meminfoThe Linux kernel provides a user-readable text file called /proc/meminfo that displays current system-wide memory performance statistics. It provides a superset of the system-wide memory statistics that can be acquired with vmstat, top, free, and procinfo; but it is a little more difficult to use. If you want periodic updates, you must write a script or some code for such. If you want to store the memory performance information or coordinate it with CPU statistics, you must create a new tool or write a script. However, /proc/meminfo provides the most complete view of system memory usage. 3.2.8.1 Memory Performance-Related OptionsThe information in /proc/meminfo can be retrieved with the following command line: cat /proc/meminfo This command displays the array of statistics described in Table 3-11. /proc/meminfo provides a wealth of information about the current state of the Linux memory subsystem. 3.8.2.2 Example UsageListing 3.17 shows an example output of /proc/meminfo. It shows some memory statistics that are similar to those we have seen with other tools. However, some statistics show new information. One, Dirty, shows that the system currently has 24KB of data waiting to be written to disk. Another, Commited_AS, shows that we need a little more memory (needed: 1068MB versus total: 1024MB) to avoid a potential out-of-memory situation. Listing 3.17.[ezolt@scrffy /tmp]$ cat /proc/meminfo MemTotal: 1034320 kB MemFree: 10788 kB Buffers: 29692 kB Cached: 359496 kB SwapCached: 113912 kB Active: 704928 kB Inactive: 222764 kB HighTotal: 0 kB HighFree: 0 kB LowTotal: 1034320 kB LowFree: 10788 kB SwapTotal: 2040244 kB SwapFree: 1756832 kB Dirty: 24 kB Writeback: 0 kB Mapped: 604248 kB Slab: 51352 kB Committed_AS: 1093856 kB PageTables: 9560 kB VmallocTotal: 3088376 kB VmallocUsed: 26600 kB VmallocChunk: 3058872 kB HugePages_Total: 0 HugePages_Free: 0 Hugepagesize: 2048 kB /proc/meminfo is the most complete place to gather system-wide Linux memory statistics. Because you can treat it as a text file, any custom script or program can easily extract the statistics. |
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%swpused kbswpcad
09:45:31 AM 11732 1022588 98.87 12636 272284 1816140 224104 10