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On Thursday, July 21 at 18:29 (-0700), Grant said: |
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> Then why not have a really big swap file? If swap is useful as a |
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> second layer of caching behind RAM, why doesn't everyone with some |
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> extra hard drive space have a 100GB swap file? |
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> |
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You've not understood what I said, I think. Swap is not useful as |
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filesystem cache. Swap is as efficient (probably a little less) than |
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the files on the disk. It's RAM that's efficient as filesystem cache. |
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Where swap comes in is the kernel can swap out pages from "stale" |
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processes, and reclaim the RAM as filesystem cache. |
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Think of it this way: You have a house with an attic. Now the attic is |
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not as "efficient" as say, the middle of your living room. You have a |
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Christmas tree, but you only use that Christmas tree maybe once a year. |
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Now it's much more efficient to keep that Christmas tree in the attic |
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for 11 months of the year and use that reclaimed space in your living |
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room for.. say a coffee table. Then, when you need that Christmas tree |
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in December, you pull it out of the attic and maybe put the coffee table |
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up in the attic for a month. |
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The Christmas tree represents a process that's just sitting out there |
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doing not much half the time, but taking up space. The space in your |
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living room is RAM, and the space in your attic is swap. The coffee |
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table is filesystem cache. |
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