Messages in this thread | | | From | "Albert D. Cahalan" <> | Subject | Re: using more than 2 GB as a ram disk | Date | Wed, 3 Feb 1999 19:56:50 -0500 (EST) |
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Alexander Viro writes: > On Wed, 3 Feb 1999, Albert D. Cahalan wrote: >> Alexander Viro writes: >>> On Wed, 3 Feb 1999, Albert D. Cahalan wrote:
>>>> I told you I was aware of that. Read the post again. >>>> Hint: at any one point in time, most segments are invalid. >>>> Another hint: the 4 kB pages need not be used at all. >>> >>> And you are going to do pagein/pageout by what chunks? >> >> 8 MB of course. :-) > > Albert, that would mean that single fscking pagein would be well beyond > the size of on-disk buffer and so platter->head transfer speed comes into > the game. Care to count the time? And that assumes that you don't have
Yes, platter->head transfer speed could become a factor. You can get 16 gigabytes of cache on a RAID box from EMC. (for those reading this with tired eyes, I wrote "giga" above)
Get some real hardware. Get the kind that kills you if it falls over.
> other traffic. Now, since you rarely have 8Mb filled with the data you'll > get ~1e4% overhead on that stuff. For most of the processes it will mean > pure and simple *swapping*.
You are thinking too small. Think of multi-gigabyte processes. The overhead for your shell would be lost in the noise. People needing this hack won't miss a few hundred megabytes of RAM.
> And it buys you what? 256Gb? Sheesh... How > many processes have RSS>8Mb? Now each of them got at least 24Mb. Great. > Oh, and COW becomes *very* interesting exercise. So fork() becomes a > bitch. Great. exec() also looks nice - you have to do at least one pagein > to start execution. Oh, and while we are at it - what will be the size of > your swap?
I'd say a half-terabyte RAID box for swap looks good. Just connect it to your I2O Fibre Channel card.
Then again, maybe you just want to keep a 60 GB process in memory. It would not be fun to thrash 60 GB.
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