On Sun, 16 Dec 2007 21:55:20 +0000 Mel Gorman wrote:
> > > Just using cp to read the file is enough to cause problems but I included
> > > a very basic program below that produces the BUG_ON checks. Is this a known
> > > issue or am I using the interface incorrectly?
> >
> > I'd say you're using it correctly but you've found a hitherto unknown bug.
> > On i386 highmem machines with CONFIG_HIGHPTE (at least) pte_offset_map()
> > takes kmap_atomic(), so pagemap_pte_range() can't do copy_to_user() as it
> > presently does.
> >
> > Drat.
> >
> > Still, that shouldn't really disrupt the testing which you're doing. You
> > could disable CONFIG_HIGHPTE to shut it up.
> >
>
> Yes, that did the trick. Using pagemap, it was trivial to show that the
> 2.6.24-rc5-mm1 kernel was placing pages in reverse physical order like
> the following output shows
>
> b: 32763 v: 753091 p: 65559 . 65558 contig: 1
> b: 32764 v: 753092 p: 65558 . 65557 contig: 1
> b: 32765 v: 753093 p: 65557 . 65556 contig: 1
> b: 32766 v: 753094 p: 65556 . 65555 contig: 1
> b: 32767 v: 753095 p: 65555 . 65555 contig: 1
>
> p: is the PFN of the page v: is the page offset within an anonymous
> mapping and b: is the number of non-contiguous blocks in the anonymous
> mapping. With the patch applied, it looks more like;
>
> b: 1232 v: 752964 p: 58944 ................ 87328 contig: 15
> b: 1233 v: 752980 p: 87328 ................ 91200 contig: 15
> b: 1234 v: 752996 p: 91200 ................ 40272 contig: 15
> b: 1235 v: 753012 p: 40272 ................ 85664 contig: 15
> b: 1236 v: 753028 p: 85664 ................ 87312 contig: 15
>
> so mappings are using contiguous pages again. This was the final test
> program I used in case it's of any interest.
>
> Thanks
>
> /*
> * showcontiguous.c
> *
> * Use the /proc/pid/pagemap interface to give an indication of how contiguous
> * physical memory is in an anonymous virtual memory mapping
> */
Matt,
Did you ever make your python pagemap scripts available?
If not, would you?
---
~Randy
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