Kernel Question: buffer cache

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2 total messages Started by Mike Battersby Sun, 06 Feb 1994 05:57

#20

Author: Mike Battersby
Date: Sun, 06 Feb 1994 05:57

27 lines
1962 bytes

First things first, a description of my setup.

        80386-40, no copro
        4mb RAM, IDE HD's (single controller), ext2 fs
        ET4000 video card
        vanilla ALPHA-pl14{p,x,z} pl15

Lately I've noticed that the amount of system memory used for the
buffer cache (as reported by 'free' or 'cat /proc/meminfo') is
behaving (at least what I see as) weirdly.  The cache size will
start out at zero, as would be expected, and slowly grow, as is
expected, but once past a certain size, will not shrink again
below that size.  This size is (usually) 1500k, but varies
depending on how many filesystems I have mounted (for example if
I unmount some filesystems, then the size will shrink).

Firstly, is this normal? If so, can somebody explain the reasons
behind this behaviour.

Secondly, if this *is* normal, doesn't such behaviour violate the
reasons for a shared memory between processes/buffer cache?  The
cache will seemingly never shrink below the given size, no matter
what the system is doing (even when it is thrashing like you
wouldn't believe), and I really don't like the idea of permanently
giving up half of my avalailble memory to the buffer cache.

 - Mike

Re: Kernel Question: buffer cache

#15

Author: Frank W. ten Wolde
Date: Sun, 06 Feb 1994 10:09

48 lines
3029 bytes

ins122a@lindblat.cc.monash.edu.au (Mike Battersby) writes:

>First things first, a description of my setup.

>        80386-40, no copro
>        4mb RAM, IDE HD's (single controller), ext2 fs
>        ET4000 video card
>        vanilla ALPHA-pl14{p,x,z} pl15

>Lately I've noticed that the amount of system memory used for the
>buffer cache (as reported by 'free' or 'cat /proc/meminfo') is
>behaving (at least what I see as) weirdly.  The cache size will
>start out at zero, as would be expected, and slowly grow, as is
>expected, but once past a certain size, will not shrink again
>below that size.  This size is (usually) 1500k, but varies
>depending on how many filesystems I have mounted (for example if
>I unmount some filesystems, then the size will shrink).

>Firstly, is this normal? If so, can somebody explain the reasons
>behind this behaviour.

>Secondly, if this *is* normal, doesn't such behaviour violate the
>reasons for a shared memory between processes/buffer cache?  The
>cache will seemingly never shrink below the given size, no matter
>what the system is doing (even when it is thrashing like you
>wouldn't believe), and I really don't like the idea of permanently
>giving up half of my avalailble memory to the buffer cache.

> - Mike

It renders my Linux useless. See my previous mail on the buffer cache
I posted one day ago. When compiling a few files my buffer cache grows
to over 2600kb, leaving only a few tens of k available for processes
to run in. Needless to say that the systems is then only busy with
paging :-(

-Frank


-- 
=============================================================================
= Frank W. ten Wolde (PA3FMT)         Pink Elephant Industry B.V.           =
= Email: franky@duteca.et.tudelft.nl  Alternative: wolde2@ksla.nl           =
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