Re: [00/41] Large Blocksize Support V7 (adds memmap support)

[Andrea Arcangeli]

On Mon, Sep 17, 2007 at 12:56:07AM +0200, Goswin von Brederlow wrote:
> When has free ever given any usefull "free" number? I can perfectly
> fine allocate another gigabyte of memory despide free saing 25MB. But
> that is because I know that the buffer/cached are not locked in.

Well, as you said you know that buffer/cached are not locked in. If
/proc/meminfo would be rubbish like you seem to imply in the first
line, why would we ever bother to export that information and even
waste time writing a binary that parse it for admins?

> On the other hand 1GB can instantly vanish when I start a xen domain
> and anything relying on the free value would loose.

Actually you better check meminfo or free before starting a 1G of Xen!!

> The only sensible thing for an application concerned with swapping is
> to whatch the swapping and then reduce itself. Not the amount
> free. Although I wish there were some kernel interface to get a
> preasure value of how valuable free pages would be right now. I would
> like that for fuse so a userspace filesystem can do caching without
> cripling the kernel.

Repeated drop caches + free can help.
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