On Tue, Apr 20, 2010 at 4:39 AM, Mel Gorman <mel@xxxxxxxxx> wrote: > On Mon, Apr 19, 2010 at 07:14:42PM +0100, Mel Gorman wrote: >> On Mon, Apr 19, 2010 at 07:01:33PM +0900, KAMEZAWA Hiroyuki wrote: >> > >> > mmotm 2010-04-15-14-42 >> > >> > When I tried >> > # echo 0 > /proc/sys/vm/compaction >> > >> > I see following. >> > >> > My enviroment was >> > 2.6.34-rc4-mm1+ (2010-04-15-14-42) (x86-64) CPUx8 >> > allocating tons of hugepages and reduce free memory. >> > >> > What I did was: >> > # echo 0 > /proc/sys/vm/compact_memory >> > >> > Hmm, I see this kind of error at migation for the 1st time.. >> > my.config is attached. Hmm... ? >> > >> > (I'm sorry I'll be offline soon.) >> >> That's ok, thanks you for the report. I'm afraid I made little progress >> as I spent most of the day on other bugs but I do have something for >> you. >> >> First, I reproduced the problem using your .config. However, the problem does >> not manifest with the .config I normally use which is derived from the distro >> kernel configuration (Debian Lenny). So, there is something in your .config >> that triggers the problem. I very strongly suspect this is an interaction >> between migration, compaction and page allocation debug. > > I unexpecedly had the time to dig into this. Does the following patch fix > your problem? It Worked For Me. Nice catch during shot time. Below is comment. > > ==== CUT HERE ==== > mm,compaction: Map free pages in the address space after they get split for compaction > > split_free_page() is a helper function which takes a free page from the > buddy lists and splits it into order-0 pages. It is used by memory > compaction to build a list of destination pages. If > CONFIG_DEBUG_PAGEALLOC is set, a kernel paging request bug is triggered > because split_free_page() did not call the arch-allocation hooks or map > the page into the kernel address space. > > This patch does not update split_free_page() as it is called with > interrupts held. Instead it documents that callers of split_free_page() > are responsible for calling the arch hooks and to map the page and fixes > compaction. Dumb question. Why can't we call arch_alloc_page and kernel_map_pages as interrupt disabled? It's deadlock issue or latency issue? I don't found any comment about it. It should have added the comment around that functions. :) And now compaction only uses split_free_page and it is exposed by mm.h. I think it would be better to map pages inside split_free_page to export others.(ie, making generic function). If we can't do, how about making split_free_page static as static function? And only uses it in compaction. -- Kind regards, Minchan Kim -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href