Benutzer:Rdiez/Linux zram - Versionsgeschichte

Rdiez: Weiterleitung nach Benutzer:Rdiez/PageRemoved erstellt

2015-05-15T19:18:47Z

Weiterleitung nach Benutzer:Rdiez/PageRemoved erstellt

Änderungen zeigen

Rdiez am 15. Juni 2014 um 08:39 Uhr

2014-06-15T08:39:16Z

Rdiez: Link auf VRAM swap

2014-06-13T16:59:32Z

Link auf VRAM swap

Rdiez am 5. Juni 2014 um 20:46 Uhr

2014-06-05T20:46:59Z

Änderungen zeigen

Rdiez am 1. Juni 2014 um 14:03 Uhr

2014-06-01T14:03:18Z

Rdiez am 1. Juni 2014 um 13:59 Uhr

2014-06-01T13:59:08Z

Rdiez am 1. Juni 2014 um 13:54 Uhr

2014-06-01T13:54:30Z

Rdiez am 1. Juni 2014 um 13:42 Uhr

2014-06-01T13:42:26Z

Rdiez am 1. Juni 2014 um 13:38 Uhr

2014-06-01T13:38:31Z

Rdiez am 31. Mai 2014 um 20:35 Uhr

2014-05-31T20:35:18Z

@@ Zeile 103: / Zeile 103: @@
 [http://en.wikipedia.org/wiki/Zswap zswap] takes the cache approach instead, so it always needs a swap device underneath. It is more flexible, as it can dynamically cache any part of the swap file, no matter how much RAM the computer has. News site ''lwn.net'' has an article titled [http://lwn.net/Articles/545244/ In-kernel memory compression] about it. Note that Ubuntu 14.04's stock kernel does not support ''zswap''.
-If your system is low on memory, you may have other options:
+If your system is low on memory, see [[Benutzer:Rdiez/Linux_Ramblings|my Linux Ramblings Page]] for more suggestions.
-* If you have more than one drive, move the swap partition or file to the least-busy disk.
-* Try swapping to a USB stick.
-* If the computer has a memory card reader, you could use a fast memory card as the main swap drive.
-* If your video card has a lot of memory, some people have managed to [https://wiki.archlinux.org/index.php/Swap_on_video_ram use some of it as a swap device].

@@ Zeile 107: / Zeile 107: @@
 * Try swapping to a USB stick.
 * If the computer has a memory card reader, you could use a fast memory card as the main swap drive.
-* If your video card has a lot of memory, some people have managed to use some of it as a swap device.
+* If your video card has a lot of memory, some people have managed to [https://wiki.archlinux.org/index.php/Swap_on_video_ram use some of it as a swap device].

@@ Zeile 65: / Zeile 65: @@
 The next thing I tried was swapping to a USB 2.0 memory stick with the following specs: 4.70 MiB/s write, 23,3 MiB/s read, 0.9 ms seek time. I noticed some improvement, but only when ''swappinness'' was set back to 60. The hard disk still rattled quite a lot, even though the system was only paging to the USB memory stick. The USB stick was apparently not fast enough.
-Firefox was the application that caused the most swapping and really killed performance. Switching to [http://en.wikipedia.org/wiki/Midori_%28web_browser%29 Midori] brought a big improvement, as long as I did not open a second web page.
+Firefox was the application that caused the most swapping and really killed performance. Switching to [http://en.wikipedia.org/wiki/Midori_%28web_browser%29 Midori] brought a big improvement, as long as I did not open a second web page. I tried [http://en.wikipedia.org/wiki/Dillo Dillo], which was very fast, but I found its interface unusable nowadays. Starting Chromium rendered the PC unresponsive for minutes. Eventually, the system killed one of the Chromium processes and complained about lack of memory, even though the machine still had 2 GiB of swap file available.
 === Swap Device Usage and Implemented Optimisations ===

@@ Zeile 65: / Zeile 65: @@
 The next thing I tried was swapping to a USB 2.0 memory stick with the following specs: 4.70 MiB/s write, 23,3 MiB/s read, 0.9 ms seek time. I noticed some improvement, but only when ''swappinness'' was set back to 60. The hard disk still rattled quite a lot, even though the system was only paging to the USB memory stick. The USB stick was apparently not fast enough.
-Firefox was the application that caused the most swapping and really killed performance. Switching to [http://en.wikipedia.org/wiki/Midori_%28web_browser%29 Midori] brought some improvement.
+Firefox was the application that caused the most swapping and really killed performance. Switching to [http://en.wikipedia.org/wiki/Midori_%28web_browser%29 Midori] brought a big improvement, as long as I did not open a second web page.
 === Swap Device Usage and Implemented Optimisations ===

@@ Zeile 63: / Zeile 63: @@
 I then tried reducing the [http://en.wikipedia.org/wiki/Swappiness swappiness] from the default 60 to 10, and that drastically increased responsiveness. The swap data size got cut down too. Enabling zswap made the swap waiting time more frequent and longer.
-The next thing I tried was swapping to a USB 2.0 memory stick with the following specs: 4.70 MiB/s write, 23,3 MiB/s read, 0.9 ms seek time. I noticed some improvement, but only when ''swappinness'' was set back to 60. The hard disk still rattled quite a lot, even though the system was only paging to the USB memory stick.
+The next thing I tried was swapping to a USB 2.0 memory stick with the following specs: 4.70 MiB/s write, 23,3 MiB/s read, 0.9 ms seek time. I noticed some improvement, but only when ''swappinness'' was set back to 60. The hard disk still rattled quite a lot, even though the system was only paging to the USB memory stick. The USB stick was apparently not fast enough.
 === Swap Device Usage and Implemented Optimisations ===

@@ Zeile 35: / Zeile 35: @@
 If the kernel decides to swap out 100 MiB of RAM contents, zram will hopefully compress it down to 40 MiB, which means that the kernel will gain 100 MiB but lose 40 MiB at the same time compared to a non-zram scenario. Therefore, the kernel will probably want to swap an extra 40 MiB out to compensate. Again, this will cause a 16 MiB memory loss. In the end, trying to swap 100 MiB out has actually moved 160 MiB to the zram disk.
-On the other hand, laptop hard disks are very slow, and writing 160 MiB to compressed RAM is probably faster than writing 100 Mib to disk. Later on, the data will need to be read back in, and that's where the speed difference really matters. Because of their high seek times, traditional hard disks are actually ill-suited for this task, as swap pages are not read in sequential blocks, but at fairly random positions. Besides, if the system is under pressure, the kernel automatically shrinks the file system cache, which also causes increased disk activity that will probably interfere with paging (assuming that you have not moved the swap area to a different drive).
+On the other hand, laptop hard disks are very slow, and writing 160 MiB to compressed RAM is probably faster than writing 100 Mib to disk. Later on, the data will need to be read back in, and that's where the speed difference really matters. Because of their high seek times, traditional hard disks are actually ill-suited for this task, as swap pages are not read in sequential blocks, but at fairly random positions. Besides, if the system is under pressure, the kernel automatically shrinks the file system cache, which also causes increased disk activity that will probably interfere with paging (assuming that you have not moved the swap area to a different drive). Keep in mind that executable pages are normally backed by a file on disk, so they are just discarded, which means paging will always cause disk activity even if the swap file is completely held in zram.
 When the 256 MiB zram device fills up, it will actually have consumed 102 MiB of RAM. Therefore, you can look at the situation this way: when under pressure, the system has lost 102 MiB of RAM, so it can only use 410 MiB instead of the physical 512 MiB. In return, the system has gained 256 MiB of very fast swap space.

← Nächstältere Version		Version vom 1. Juni 2014, 13:38 Uhr
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	I then tried reducing the [http://en.wikipedia.org/wiki/Swappiness swappiness] from the default 60 to 10, and that drastically increased responsiveness. The swap data size got cut down too. Enabling zswap made the swap waiting time more frequent and longer.		I then tried reducing the [http://en.wikipedia.org/wiki/Swappiness swappiness] from the default 60 to 10, and that drastically increased responsiveness. The swap data size got cut down too. Enabling zswap made the swap waiting time more frequent and longer.
		+
		+	The next thing I tried was swapping to a USB 2.0 memory stick with the following specs: 4.70 MiB/s write, 23,3 MiB/s read, 0.9 ms seek time. I noticed some improvement, but only when ''swappinness'' was set back to 60. The hard disk still rattled quite a lot, even though the system was only paging to the USB memory stick.

	=== Swap Device Usage and Implemented Optimisations ===		=== Swap Device Usage and Implemented Optimisations ===

@@ Zeile 41: / Zeile 41: @@
 If your software permanently accesses 450 MiB of memory, zram will drastically reduce performance. But that's not the normal scenario. Typically, if you keep a number of big applications like Firefox or LibreOffice running all the time, you will probably experience heavy swapping whether you have 410 or 512 MiB of physical memory. But that kind of software does not need all the allocated memory all the time. As long as your virtual memory needs do not exceed 666 MiB (that is 410 + 256), then zram will probably make your system faster overall. If your software needs more than 666 MiB, it will start paging out to disk, and that part will be as slow as before.
-The trick is to achieve the right trade-off between RAM size, CPU performance, virtual memory requirements and hard disk speed. Your mileage may vary. I did a quick test on a 512 MiB, dual-core PC running Xubuntu 14.04, Firefox (with one longish web page), LibreOffice Writer and Calc (with empty documents), Synaptic, KSysGuard and a Terminal. Just switching between the applications always causes heavy paging the first time around, and my subjective impression was that performance was slightly worse with zram enabled. The 256 MiB zram device was not enough and another 126 MiB's worth of swap data landed on disk. I was surprised how quickly the swap data size grew when the system was under pressure. I never thought you would need so much virtual memory to run that set of applications.
+The trick is to achieve the right trade-off between RAM size, CPU performance, virtual memory requirements and hard disk speed. Your mileage may vary.
 === Swap Device Usage and Implemented Optimisations ===