Tag Archives: Windows 7

How to measure Windows 7 Memory Usage

I did a memory usage test of Windows 7 64 bit with 4 GB RAM. Since Windows 7 takes advantage of more RAM, let’s see the result if we test with 8 GB RAM. If you are using 8 GB RAM for your VDI sizing, this test will be more applicable than the test with 4 GB RAM because Windows 7 will make use of the extra RAM. It is smart enough to utilised the hardware since it’s already given to it.

BTW, if what you want is Windows 2008, see this.

Both tests (4 GB and 8 GB) were conducted on physical desktops. I did it on physical so we know for sure there is no hypervisor impacting any reading here. I know VMware VMkernel will not impact the reading, but to assure some readers, I decided to eliminate that layer altogether. The 2 desktops are not identical but they have the same set of applications. The 8 GB desktop drives a 4K monitor, while the 4 GB desktop drives a Full HD monitor. I’m not sure if the 4K display impacts RAM, as I thought it uses the video RAM instead. One thing for sure, it’s much easier to review on 4K display!

In my system, since I used SSD, SuperFetch is disabled. This informative post provides details on SuperFetch. BTW, if you are using VDI, the Horizon 6 manual recommends disabling it. The reason is “By disabling the Windows prefetch and superfetch features, you can avoid generating prefetch files and the overhead associated with prefetch and superfetch operations. This action can reduce the growth of linked-clone machines and minimize IOPS on full virtual machines and linked clones”

With that, let’s dive to the test.

Screenshot #1

11 starting

  • I boot up the machine, and let it idle for a few minutes to ensure all start up programs have finished running. I want them to “settle down”…
  • Windows 7 makes use of all the physical RAM. The 8 GB desktop takes 1 GB more RAM compared with the 4 GB desktop. I do not have any applications running and have listed all the processes shown in Task Manager. Windows 7 takes up 3 GB right away.

Screenshot #2

13 Free did dropped to 0 for 1 second

  • I performed a similar test to the one I did on the 4 GB desktop. Essentially, I launched a lot of common apps, and opened lots of large files (>10 MB on average). For the video, I opened a 650 MB video.
  • I also forced PowerPoint to load all the slides, by going into slide sorter and made it draw all slides.
  • Naturally, CPU and Disk would spike, so I let them settle down first. My focus here is RAM.
  • The screenshot is taken after Windows 7 settles down. As you can see, CPU metrics have gone down for all processes. PowerPoint, Visio, Adobe, Word, etc. have gone down to 0%, as they are done opening files.
  • Surprisingly, Windows 7 still have 1.5 GB of free RAM. This tells me that 6.5 GB is comfortable.

Screenshot #3

13 Free did dropped to 0 for 1 second

  • Just in case you think 8 GB RAM is too much, you can easily hit it by opening more applications and files. In the screenshot above, the Free memory dropped to 61 MB. It actually touched 0 MB for a second. Windows did not seem to like the 0 value and would move some pages out.
  • The screenshot was again taken after CPU and Disk stabilised. The RAM is also stable around 6 GB. Windows “Used Physical Memory” graph at the top right does not take into account Standby Memory.
  • Should you take into account Standby? That seems debatable.

Screenshot #4

15 commit RAM also stable

  • There is another way to know if Windows needs more RAM. I recommend you read this excellent article by Ed Bott. The link to the screenshots is not working, which is one reason I recreated my own.
  • From the PerfMon, I can see that my Commit Limit is 16 GB. Commit Limit = Physical RAM + Virtual RAM. In my case, that’s 8 GB of RAM and 8 GB of PageFile.sys. So 16 GB is all I have.
  • % Committed is what is currently committed / Commit Limit. In my case, Windows commits 6.2 GB. The value is stable, so the % Committed is stable at 38%.
  • Should you use your Virtual RAM? There are different opinions on the Internet. I personally prefer what I recommend at the end of this blog.
  • BTW, the pagefile.sys is typically located in C:\ directory. It’s hidden, just like the file for hibernation. By default, Windows 7 automatically manages the pagefile. I notice the same behaviour in Windows 8.1. Both basically creates a pagefile the size of your physical RAM. Whether pagefile is good or bad, that is again debatable…. My experience is at 8 GB, you need it. Windows 7 performs poorer without it.
  • One thing for sure. Pagefile is not swap file. Swap file is used when Windows runs out of physical RAM. Pagefile is used proactively. Just because you’re seeing activity in pagefile.sys does not mean Windows is running out of RAM.

Screenshot #5

16 impact of closing all apps

  • To complete the test, I closed all applications. You can see in the top right corner, the chart changes in value in tandem as Windows closed the applications.
  • Interestingly, the usage did not go back to original. Windows is using ~4.6 GB of RAM. I think some applications do not actually leave the RAM. Skype, Chrome are examples of such applications. I have seen Chrome taking up >1 GB of RAM if you let it run for days.
  • BTW, Windows 7 keeps the pages in the Standby memory. It does not move it out after a few minutes. To me, this makes engineering sense. It is the same strategy adopted by ESXi VMkernel, which is why you see the Memory Consumed counter to be high.

Screenshot #6 (video)

22 normal playing does not result in growing RAM - it is steady with minimal page fault

  • I’m curious the impact of playing video on RAM. I played a 650 MB video. Surprisingly, it did not occupy 650 MB. In fact, it occupied only 360 MB. How I know is the Free memory dropped by 360 MB. I played the video in full size (1:1), not full screen, which explains why it did not occupy the full screen as it’s 4K display.
  • During the play, the memory counter did not slowly go up. It remains essentially the same, as you can see above.
  • I thought perhaps because I was simply watching the video normally (sequentially). So I jumped along the video, forcing it to play randomly. I would click toward the end, let it play, then immediately click somewhere at the beginning. It is a 27 minutes video, so I have plenty of timeline to click. It’s interesting to see that this random jump does not result in page fault. It is as if the entire video is already in memory. The counter Hard Faults/sec barely moved. Perhaps it was reading from disk directly?

Conclusion

  • If you want the best performance, use Total – Free as the sizing.
  • If you want a more cost effective solution, use Total – Free – Standby.  This would result in around 1-3 GB less RAM.
  • Let Windows manage the pagefile. This is the default setting anyway. I noticed a visibly slower performance even though Windows showing >1 GB of Free memory. In fact, Windows gave error message, and some applications crashed.
  • The % Committed metric should not hit 80%. Performance drops when it hits 90%, as if it’s a hard threshold used by Windows. If you use a pagefile, you will not hit this limit.
  • In general, I’d size Windows 7 between 4 – 8 GB of RAM, depending on the users. I’d use the following guidelines
    • 4 GB for light user
    • 8 GB for average
    • 12 GB for heavy. Yes, that’s 12 GB as I’ve seen my customers hit near 0 Free Memory, and he is just a “normal, average user”. He is an IT Manager.

Additional Resource

You might be wondering what those memory counters mean in Task Manager. Naveed Qadri explains it well here, so please read it.

  • Cached = Standby + Modified
  • Available = Standby + Free
  • Free = Free + Zero.

The difference between Cached and Available is Cached uses Modified, while Available uses Free. Available means exactly what the word means. It is the amount of physical memory immediately available for used.

Another article on Windows 7 memory management that I found useful was one written by Brandon Paddock. You can find it here. He wrote a program that proves that Commit can go up without In Use going up. I’m going to quote a sentence, so you can find it in his blog.

“Notice how my physical memory usage is unchanged, despite the fact that Commit has now increased by the full 2.3GB of that file."

Committed RAM can go beyond the physical RAM, as it takes into account pagefile.sys. The Commit Limit is typically 2x your physical RAM. In the example that Brandon gave:

"In fact, my commit value is now 6GB, even though I have only 4GB of physical memory and less than 3GB in use.”

Mark Russinovich explains in this technet blog something that you need to know. There is Reserved memory, and then there is committed memory. Some applications like to have its committed memory in 1 long contiguous block, so it reserves a large chunk up front. I can think of Databases and JVM in this example. This reserved memory does not actually store meaningful application data or executable. Only when the application commits the page that it becomes used. Mark explains that “when a process commits a region of virtual memory, the OS guarantees that it can maintain all the data the process stores in the memory either in physical memory or on disk”.

Notice the word “on disk“. Yes, that’s where the pagefile.sys comes in. Windows will use either the physical memory or the pagefile.sys.

Right-sizing Windows 7 RAM

Right-sizing RAM is certainly a common requirement, as we know VM tend to be oversized. However, we need to be careful when reducing RAM. Reducing RAM on VM based on information at the hypervisor level can result in poor performance. You need to have in-guest level data.

I did a set of test on a physical desktop to see Windows memory behaviour. I did it on physical so we know for sure there is no hypervisor impacting any reading here.

I have 64 bit Windows 7 on a physical desktop with 4 GB RAM. For a test on 8 GB RAM, see this as the result is not the same, even though the workload is similar.

Screenshot #1

1 - Win 7 - after boot - stable - 0 page fault

  1. I boot up the machine, and let it idle for a few minutes to ensure all start up programs have finished running. I want them to “settle down”…
  2. Modified (orange), based on this excellent article, means memory that can be used by other programs, but Windows needs to write to the page file before they can be reused. If that is true, I wonder why it is called modified.
  3. The screenshot shows that Windows 7 64 bit uses 1296 MB of RAM (162 + 1055 + 79). The Standby Memory means it contains cached data that is no longer actively in used. How does Windows define “actively in used” is not clear. If a block of RAM is not used in the past 1 minute, is it active? How about 10 minutes? 1 hour? The next few screenshots will clarify that.
  4. We have 674 MB of Standby and 2126 of Free as you can see above.

Screenshot #2

2 - Win 7 - after opening lots of files and apps - CPU

  1. I then launched a lot of common apps, and open lots of files. I opened 13 large PowerPoint files and 10 Adobe PDF files. You can see in the screenshot, the task bar is full of documents.
  2. Naturally, CPU and Disk would spike, so I let them settle down first. My focus here is RAM.
  3. The screenshot is taken after Windows settles down.
  4. You notice CPU has gone down. My desktop has 4 cores, and 2 cores are actually parked. You can see that the only CPU-consuming process is the Resource & Performance Monitor itself, and the Desktop Window Manager, as it has to redraw the screen.
  5. Both PowerPoint and Adobe has gone down to 0%, as they are done opening files.

Screenshot #3

3 - Win 7 - after opening lots of files and apps - RAM stable

  1. After verifying that CPU has settled down, I verify the RAM.
  2. Unlike CPU, we have a very different situation here for RAM. This is key to explaining why you cannot just downsize RAM without consulting application team.
  3. Windows now use 2553 MB. Much higher than 1296. Obviously the executables of PowerPoint, Adobe, Excel are in the RAM.
  4. The Free Memory has gone down from 2126 to just 469 MB.
  5. The Standby Memory increases from 674 to 1074. This is the 23 ppt/pdf files that were opened and after that not touched by. All I did was just opened them. So from here we can tell that “active” is a relatively short time, it’s in seconds or minutes. In my subsequent observation, it is actually in seconds.

Screenshot #4

4 - Win 7 - after forcing powerpoint to draw all slides by going into slide sorter view and scroll - same with adobe - RAM increase

  1. Based on screenshot #3 (not #4), I could conclude whether PowerPoint or Adobe read the entire files. I think it reads more than the first page or the first slide, but probably not all. I knew from other tests that 1 MB of powerpoint file translates to 15 MB in RAM. I still have 469 MB of Free RAM, while I think it should be lower.
  2. So I forced PowerPoint to read the entire content of almost every files. What I did what go to each file, change to “Slide Sorter” view, wait until PowerPoint redraws all slides, scroll down, wait until it redraws, repeat until the last slide is drawn. This ensures PowerPoint read every slide, and brought it to RAM. I did the same thing some of the Adobe file.
  3. The Free RAM dropped from 469 MB to just 9 MB. It’s interesting it does not go down to 0. This is showing Windows memory management. The Standby remains high, from 1074 to 953. This is a proof that “active” is a relatively short time.

Screenshot #5

5 - Win 7 - after idling for 40 minutes - RAM is still high because there is no pressure to release

  1. I let my desktop idle for 40 minutes. Naturally, Windows went to sleep mode after a while. I wanted to see the effect of sleep mode on RAM.
  2. When I brought up Windows from Sleep mode, I checked the RAM. Screenshot #5 shows that it’s hardly change. The Free RAM remains low, Standby is about the same, and In Use is about the same.
  3. It looks like Windows treat executables differently than it does data. I think the In Use Memory is the apps, and not the data. However, I’m not 100% sure here.
  4. It is confirmed that Sleep does not flush the RAM content.
  5. I am not able to check page fault as Resource Monitor does not have it. But when I use PerfMon, I can see paging.
  6. You can see paging at vCenter if you separate the page file into its own vmdk file. This is something you should consider as standard. You can then use vRealize Operations to monitor for abnormal behaviour. For example, the VM owner complains that the VM became slower since last weekend change. You do not see any significant difference in memory, CPU, Disk or network utilisation. Your ESXi host was healthy too, delivering very low contention. However, vRealize Operations shows abnormal behaviour in the vmdk file that hosts the page file (and only the page file). It has much higher read and write. From here you can at least say that there is excessive paging. This topic is covered in depth here.

Screenshot #6

6 - Win 7 - after closing all apps - RAM is cleared

  1. I closed all apps. As expected, the memory got back to near the original situation, when I had no apps open.

Screenshot #7

7 - Win 7 - after launching PowerPoint and open 8 MB file

  1. I launch PowerPoint again, but this time only open 1 file (8 MB). I do not launch other apps.
  2. Notice the Standby Memory remains the same. So Windows keeps it, and uses the Free Memory instead. This makes sense.

Screenshot #8

8 - Win 7 - Standby and Free do not reduce even if we use more than 4 GB

  1. I launched Visio installer and OpenOffice installer. Total 560 MB file.
  2. I also launched Word, Adobe, etc.
  3. I notice Windows Free Memory did touch 0 MB for 1 second, and then Windows keeps it above it. You notice in the screenshot that the Standby Memory actually goes up by around 500 MB.
  4. This confirms that Standby is adjusted in seconds, not minutes. This means Active is in seconds too.

Screenshot #9

9 - Win 7 - Closing installer software removes 500 MB from RAM

  1. I closed both the installer programs.
  2. The Active memory (In Use) remains the same.
  3. The Free Memory goes up by around 500 MB, while Standby drops by 500 MB.
  4. This means we know the installer was in the Standby Memory.

Screenshot #10

10 - Win 7 - Closing 25 MB of ppt files frees up 380 MB

  1. I closed 25 MB worth of PowerPoint files.
  2. The Standby remains the same, so we know the files were not in Standby. They were in “In Use”, as it drops and the Free Memory goes up by 380 MB.

Conclusion:

  1. Memory tends to stay even though it is not used. It is much more stable than CPU. This is because Windows does not know when it will be used again, so it just keeps the pages there, just in case. This makes sense. So the RAM remains idle.
  2. Because they are idle, the Hypervisor (VMkernel) will think they are not used. Remember the hypervisor has no visibility inside the Guest OS memory list. The Memory Usage counter in vCenter will give you a low number. If you are sizing based on this, it can impact performance, as it can force paging inside Windows.
  3. For Windows, you need to use the Free Memory counter, In Use counter, and Standby counter to give a more accurate picture. For optimum performance, I’d include Standby in the sizing as that’s serving as cache