210773 - memory cache in use exceeds maximum

Status: VERIFIED DUPLICATE of bug 198806

(Core :: Networking: Cache, defect)

Description

[Colin Blake]

As reported in bug 210481, the memory cache size can exceed its limit. Here's
what I currently have:

  Memory cache device

  Number of entries: 	43
  Maximum storage size: 8192 k
  Storage in use: 	13744 k
  Inactive Storage: 	0 k

This is on OpenVMS using 1.4-RC3, but I observe the same behaviour on Linux
running 1.4-RC1. Just have "about:cache" open in one tab, and browse around a
bit in another tab, and keep refreshing the about:cache tab. Shouldn't take long
before you see "in use" greater than "maximum".

Comment 1

[Jo Hermans]

*** This bug has been marked as a duplicate of 198806 ***

Comment 2

[Colin Blake]

Maybe bug 198806 should be given a better summary, then I might have found it.

Comment 3

[gordon]

Well, it's not clear that this a duplicate of bug 198806.  The fact that
"Storage in use" can be greater than "Maximum storage size" sometimes indicates
a problem, but it can also be perfectly normal.  The memory cache values need to
be relabeled so they don't needlessly generate invalid bugs.

The memory cache will accept any decompressed images ImgLib is currently
displaying (has referenced) regardless of size.  Since ImgLib has already
aquired the memory for them, we might as well share them via the cache.  As soon
as they are no longer referenced, they will get evicted.  So the "Maximum
storage size" only applies to a quiescent state where currently displayed
decompressed images require less than that Maximum.

To see if there is really a problem when "Storage in use" exceeds "Maximum
storage size", you need to look at the actual entries in the memory cache.  If
there are entries that are not currently used in a tab/window, then something is
 inappropriately holding a reference to it, and a bug should be filed.

Comment 4

[benc]

V/dupe.