I don't know the answers to your questions, however, you probably don't want RAM disks anyway.
The kernel does a _great_ job of managing what's in memory and what isn't. In fact, I'm not sure having a RAM disk keeps it in RAM - it _may_ keep it in swap (i.e. - on disk). If your RAM disks are using all of you memory, you may end up swapping your programs like crazy. Anyway, all free memory is used by the kernel for buffers, making RAM disks fairly useless. Jon On Wed, 18 Jun 2003, Robert P. J. Day wrote: > > i'm trying to figure out what i can and can't do with > ram disks, so let me explain what i've found so far, and > perhaps someone can fill in the gaps. > > by "ram disk", i don't mean the boot-time initrd image. > i mean setting aside an arbitrary amount of RAM, formatting it > as an ext2/3 filesystem, mounting it, filling it with files, > and then having smokin' fast access to those files. > > (as an aside, i wanted to test this by creating a ram > disk big enough for the kernel source directory, to see > just how much faster a kernel build would run.) > > so, under RH 9 and with the 2.5.72 kernel, i can see > the kernel option for "RAM disk support", and a default > size of 4096 (kilobytes, or 4M). > > from what i've read, i can create a number of ram disks > corresponding to /dev/ram[012345...], by doing the following: > > # dd if=/dev/zero of=/dev/ram0 bs=1024 count=16 > > for a tiny ram disk of 16k (supposedly). so what actually > happens? > > if i try to create an ext2 filesystem on it: > > # mke2fs /dev/ram0 > > it works, but it's obvious that it's 4M in size -- the > default. i didn't *ask* for the default size, i was hoping > i could pick the size myself. but i get 4M anyway. > > (i can mount that filesystem, and "df" shows the same > thing: 4M). > > the same thing happens no matter what size i use for > "dd", until i try to go over 4M, at which point, at the 4097th > write (just past 4M), i get "No space left on device". > > in short, no matter what i ask for, i'll get a 4M ram disk. > so, the questions: > > 1) is there any way to create a ram disk of an arbitrary size, > regardless of the kernel config value for default size? > > 2) once i create a ram disk, is there an indicator that tells > me that such a thing exists? i mean, "free" will show me > that there's less free space, but that's about it. is there > maybe an entry under /proc keeping track of ram disks? > you know ... maybe /proc/list_of_ram_disks?? :-) > > 3) once i create one (even if i'm still stuck with 4M), how > can i manually release it? and again, is there a way to > verify the return of that ram disk space to the OS? > > > > rday > > -- > > Robert P. J. Day > Eno River Technologies > Unix, Linux and Open Source training > Waterloo, Ontario > > www.enoriver.com > > > -- > redhat-list mailing list > unsubscribe mailto:[EMAIL PROTECTED] > https://www.redhat.com/mailman/listinfo/redhat-list > -- redhat-list mailing list unsubscribe mailto:[EMAIL PROTECTED] https://www.redhat.com/mailman/listinfo/redhat-list
