Messages in this thread | | | Subject | Re: mmapping large files hits swap in 2.4? | From | Daniel Egger <> | Date | 12 Aug 2002 13:41:56 +0200 |
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Am Mon, 2002-08-12 um 11.11 schrieb Helge Hafting:
> In short - memory used to cache your big mmapped file don't merely > compete with memory used for caching other parts of that file. > It competes with all other swappable (or discardable) memory > in the system, and some of that might go to the swap device.
That's what I though.
> Maybe you only need a little of that big file at a time - but > the VM system cannot know that. It simply looks at _all_ > memory, considers "what is recently used, and what is _not_" > and goes on to swap/writeback the latter parts.
Actually I need 95% and the file will grow on demand so it's pretty hefty in use; I really need to invent some hack to avoid touching the memory as much as we do now without any need.
> You have enough RAM, but was all of it _free_ according to free? > Lots of it will usually be in use as cache, so something must be > evicted. Cache are freed sometimes, swapping happens at > other times.
Interestingly the behaviour seems to be quite different on PPC vs. i386. On my PPC machine with 256 MB RAM I have constant use swap and all of the "free" memory is used as cache. On a i386 maschine with 512MB RAM the kernel never touched a single byte of swap and around 150MB are always free. Both machines always have a load > 1 and are used for big compile jobs like gcc, OpenOffice and alike. -- Servus, Daniel
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