Nikolaus Rath <nikol...@rath.org> writes: > Thomas Goirand <z...@debian.org> writes: >> On 05/25/2012 05:33 PM, Mehdi Dogguy wrote: >>>> What if we're installing Debian on a very small system, and that we >>>> need operations with big files in /tmp? >>>> >>> >>> Increase your swap? >> >> So, in this case, we will have the following scenario: >> - An app writes in /tmp >> - There's not enough space, so the system starts swapping, >> including some apps.
Which happens regardless wether tmp is tmpfs or a real filesystem. The more IO there is the more likely some app gets swapped out. >> - The file gets written to /tmp, then gets read >> - Finally, the file gets deleted With tmps that instantly frees up all the memory and swap used by the file. With a real FS the file data remains in the dirty cache until such a time as the disk has cought up with writing it all and then it is thrown away. So potentially memory is freed up much later. >> - Then we have randomly very sloppy reaction of apps >> that were swapped out so that the file could be written >> in /tmp. Which, without tmpfs, then has to additionaly first wait for the dirty cached data to be written out causing huge delays because you get two seeks per page, 4k read/writes and no read-ahead. > I believe tmpfs memory is swapped out preferentially, so your scenario > doesn't have to play out like that. However, paging being a complex > process, it's not impossible either. Is that something people are > actually seeing? Because I haven't encountered this. It happens. But that isn't to say it doesn't equally (or worse) happen with a real FS. Paging is a complex process and there are so many factors involved that predicting the behaviour becomes pure guesswork. I would say both Thomas and my scenario are equally likely to occur. No matter what the default is there will be some users that hit the worst case. MfG Goswin -- To UNSUBSCRIBE, email to debian-devel-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org Archive: http://lists.debian.org/87d35jmgf9.fsf@frosties.localnet