Re: Free vs Unused pages?
Linus Torvalds (torvalds@transmeta.com)
Mon, 25 Aug 1997 12:29:46 -0700 (PDT)
On Mon, 25 Aug 1997, Bill Hawes wrote:
> Benjamin C R LaHaise wrote:
> > Pages that are allocated but have a use count of zero are of order >0 -
> > only the first page of such chunks actually have a use count of 1
> > (anything else would just be evil). Hope that clears it up for you!
>
> Thanks, much clearer now. But my next question would be how to
> distinguish such order > 0 pages from memory-leaked pages. I'd like to
> modify the show_mem function so that its "free pages" count exactly
> agrees with the freelist, in the absence of leaks.
>
> When an order > 0 page is released, does the memory allocator sweep up
> all trailing adjacent pages with count = 0 and assume they were part of
> the initial allocation?
No, it uses the buddy system bitmaps, and depends on the fact that you
always release the same order as you allocated.
So to really see what's free or not, you have to look at the bitmaps in
addition to the page counts.. Maybe somebody can come up with a good way
of doing all this, I certainly can't think of anything offhand,
Linus