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>> So swap isn't treated exactly like RAM. It actually has special |
| 2 |
>> handling in Linux which makes it beneficial to have on almost any |
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>> Linux system? According to Alan, things get very bad when a Linux |
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>> system hits swap. How can behavior like this be beneficial: |
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>> |
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>> "When a linux machine hits swap, it does so very aggressively, there |
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>> is nothing nice about it at all. The entire machine slows to a |
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>> painstaking crawl for easily a minute at a time while the kernel |
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>> writes pages out to disk, and disk is thousands of times slower than |
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>> RAM. |
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>> |
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> This is not entirely true. There's regular swapping and there is |
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> "thrashing". Thrashing is indicative of a memory-starved system, i.e. |
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> when many processes are trying to access memory, but there just isn't |
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> enough and the system is frantically swapping in/out. I'm talking about |
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> your normal day-to-day swapping that you probably don't even notice. |
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> |
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>> It gets so bad that you can't even run a shell properly to try and see |
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>> what's going on and kill the actual memory hog." |
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> |
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> Again, that is thrashing. I'm talking about "normal" swappage. Dont |
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> throw the baby out with the bath water. |
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> |
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>> Also, aren't you likely to wear out your hard disk sooner using swap? |
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> |
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> Is this coming from someone who uses Gentoo linux, which is constantly |
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> downloading/compiling/linking object files? Syslog and other loggers |
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> writing everything under the sun to a log file. Backups, journal |
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> writes, database transactions, etc. Compare how many disk transactions |
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> take place during your normal Gentoo usage versus a few megabytes |
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> here/there being swapped in/out. Again, I'm talking about regular |
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> swapping, not "oh my god I has no RAM and my hard drive won't stop" |
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> Even so, we're talking about modern drives here. This isn't the 1960s. |
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|
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If I understand correctly, an out-of-memory condition that would lock |
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up a system without swap, will cause it to thrash with swap. A remote |
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system of mine was locked up for many hours due to running out of |
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memory without swap. If I had enabled swap, the system would have |
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thrashed for those hours? |
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|
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- Grant |
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