Messages in this thread | | | From | KOSAKI Motohiro <> | Subject | Re: Swappiness vs. mmap() and interactive response | Date | Tue, 28 Apr 2009 14:35:29 +0900 (JST) |
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(cc to linux-mm and Rik)
> Hi, > > So, I just set up Ubuntu Jaunty (using Linux 2.6.28) on a quad core phenom box, > and then I did the following (with XFS over LVM): > > mv /500gig/of/data/on/disk/one /disk/two > > This quickly caused the system to. grind.. to... a.... complete..... halt. > Basically every UI operation, including the mouse in Xorg, started experiencing > multiple second lag and delays. This made the system essentially unusable -- > for example, just flipping to the window where the "mv" command was running > took 10 seconds on more than one occasion. Basically a "click and get coffee" > interface.
I have some question and request.
1. please post your /proc/meminfo 2. Do above copy make tons swap-out? IOW your disk read much faster than write? 3. cache limitation of memcgroup solve this problem? 4. Which disk have your /bin and /usr/bin?
> > There was no particular kernel CPU load -- the SATA DMA seemed fine. > > If I actively used the GUI, then the pieces I was using would work better, but > they'd start experiencing astonishing latency again if I just let the UI sit > for a little while. From this, I diagnosed that the problem was probably > related to the VM paging out my GUI. > > Next, I set the following: > > echo 0 > /proc/sys/vm/swappiness > > ... hoping it would prevent paging out of the UI in favor of file data that's > only used once. It did appear to help to a small degree, but not much. The > system is still effectively unusable while a file copy is going on. > > From this, I diagnosed that most likely, the kernel was paging out all my > application file mmap() data (such as my executables and shared libraries) in > favor of total garbage VM load from the file copy. > > I don't know how to verify that this is true definitively. Are there some > magic numbers in /proc I can look at? However, I did run latencytop, and it > showed massive 2000+ msec latency in the page fault handler, as well as in > various operations such as XFS read. > > Could this be something else? There were some long delays in latencytop from > various apps doing fsync as well, but it seems unlikely that this would destroy > latency in Xorg, and again, latency improved whenever I touched an app, for > that app. > > Is there any way to fix this, short of rewriting the VM myself? For example, > is there some way I could convince this VM that pages with active mappings are > valuable? > > Thanks.
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