SUMMARY: Where's my memory going?

From: Dave Sill (
Date: Tue Nov 17 1998 - 11:26:55 CST

I wrote:

    [Solaris 2.5.1, ULTRA Enterprise 2, 896MB RAM, DCE 1.1]
    This system is eating RAM for breakfast, lunch, and supper, and I
    can't figure out where it's going. It was thrashing badly with
    128MB, not as badly with 256MB or 896MB. Adding up the resident
    sizes yields less than 100MB.
    I'd appreciate any information that would help me figure out
    what's going on here, and how I can fix it. Let me know if you
    need further info.

And included copies of top, vmstat, ps, and sar output.

The bottom line is that the memory is being used for buffer
cache. Casper Dik wrote:

>It's filesystem cache. The system will not throw away cached
>data until it runs out of free pages.
>The only reliable measurement of memory shortage is the scan
>Memory is seldom freed (except when applications exit and their
>private anonymous memory becomes unreferenced)

A couple people suggested using memtool,, to see where it was being
used. I did, and it worked great.

I also discovered that 2.6 and 7/2.7 have an improved paging algorithm
called "priority paging" that helps keep the buffer cache from using
too much memory (it's not available for 2.5.1 yet). See for
more details.

Thanks to everyone who replied.


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