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Re: Debian shared libs use far more memory than required

Thiemo Seufer wrote:

Andreas Barth wrote:
11 .rodata      000840cb  000000000021a180  000000000021a180   ...
21 .data         000233c0  00000000003f1d60  00000000003f1d60  ...

11 .rodata       000a43ad  00000000001f3180  00000000001f3180  ...
21 .data         00000748  00000000003f3460  00000000003f3460  ...

That's 0x0233c0-0x748 = 140KB moved from shared to non-shared

140KB of non shared memory per GTK application is HUGE!!!

Fortunately it is not as bad as it sounds iff the constant data is
collated together in larger chunks. The kernel does copy-on-write,
if a .data page is never written, the memory usage is effectively
the same.

I checked the content of the .data section in libgtk and the
unexpected data appears to  be composed of all exported
symbols aligned to a multiple of 16.  Obviously a symbol
table of some kind.

Unfortunately, they only seem to be grouped per object file.
Some small non-constant data can be found every few KB.
I made a quick estimation and it seems that writing to those
non-constant data would access about 15 pages or 60K with
a 4K page size. Not as bad as the initial 140KB but still impressive.

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