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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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> |
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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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That all makes perfect sense, but if a small swap is good and a large |
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swap is not any better, I'm missing something. Maybe the pages from |
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stale processes never total more than a small amount? I don't see how |
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that could be. |
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- Grant |
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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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> |
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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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