On Tue, Apr 20, 2010 at 5:20 PM, Mel Gorman <mel@xxxxxxxxx> wrote: > On Tue, Apr 20, 2010 at 11:39:46AM +0900, Minchan Kim wrote: >> 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? > > In theory, it isn't known what arch_alloc_page is going to do but more > practically kernel_map_pages() is updating mappings and should be > flushing all the TLBs. It can't do that with interrupts disabled. > > I checked X86 and it should be fine but only because it flushes the > local CPU and appears to just hope for the best that this doesn't cause > problems. Okay. >> 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). > > I considered that and it would not be ideal. It would have to disable and > reenable interrupts as each page is taken from the list or alternatively > require that the caller not have the zone lock taken. The latter of these > options is more reasonable but would still result in more interrupt enabling > and disabling. > > split_free_page() is extremely specialised and requires knowledge of the > page allocator internals to call properly. There is little pressure to > make this easier to use at the cost of increased locking. > >> If we can't do, how about making split_free_page static as static function? >> And only uses it in compaction. >> > > It pretty much has to be in page_alloc.c because it uses internal > functions of the page allocator - e.g. rmv_page_order. I could move it > to mm/internal.h because whatever about split_page, I can't imagine why > anyone else would need to call split_free_page. Yes. Then, Let's add comment like split_page. :) /* * Note: this is probably too low level an operation for use in drivers. * Please consult with lkml before using this in your driver. */ > > -- > Mel Gorman > Part-time Phd Student Linux Technology Center > University of Limerick IBM Dublin Software Lab > -- 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