On Tue, Apr 20, 2010 at 12:07 PM, KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote: > On Tue, 20 Apr 2010 11:39:46 +0900 > Minchan Kim <minchan.kim@xxxxxxxxx> 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? It's deadlock issue or latency issue? >> I don't found any comment about it. >> It should have added the comment around that functions. :) >> > > I guess it's from the same reason as vfree(), which can't be called under > irq-disabled. > > Both of them has to flush TLB of all cpus. At flushing TLB (of other cpus), cpus has > to send IPI via smp_call_function. What I know from old stories is below. > > At sendinf IPI, usual sequence is following. (This may be old.) > > spin_lock(&ipi_lock); > set up cpu mask for getting notification from other cpu for declearing > "I received IPI and finished my own work". > spin_unlock(&ipi_lock); > > Then, > CPU0 CPU1 > > irq_disable (somewhere) spin_lock > send IPI and wait for notification. > spin_lock() > > deadlock. Seeing decription of kernel/smp.c::smp_call_function_many(), it says > this function should not be called under irq-disabled. > (Maybe the same kind of spin-wait deadlock can happen.) > Thanks for kind explanation. Actually I guessed TLB issue but I can't find any glue point which connect tlb flush to smp_call_function_xxx. :( Now look at the __native_flush_tlb_global. It just read and write cr4 with just mask off X86_CR4_PGE. So i don't know how connect this and smp_schedule_xxxx. Hmm,, maybe APIC? Sorry for dumb question. -- 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