On Mon, Feb 15, 2016 at 11:07:41AM -0500, Steven Rostedt wrote: > On Mon, 15 Feb 2016 12:04:50 +0900 > js1304@xxxxxxxxx wrote: > > > From: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> > > > > CMA allocation should be guaranteed to succeed by definition, but, > > unfortunately, it would be failed sometimes. It is hard to track down > > the problem, because it is related to page reference manipulation and > > we don't have any facility to analyze it. > > > > This patch adds tracepoints to track down page reference manipulation. > > With it, we can find exact reason of failure and can fix the problem. > > Following is an example of tracepoint output. > > > > <...>-9018 [004] 92.678375: page_ref_set: pfn=0x17ac9 flags=0x0 count=1 mapcount=0 mapping=(nil) mt=4 val=1 > > <...>-9018 [004] 92.678378: kernel_stack: > > => get_page_from_freelist (ffffffff81176659) > > => __alloc_pages_nodemask (ffffffff81176d22) > > => alloc_pages_vma (ffffffff811bf675) > > => handle_mm_fault (ffffffff8119e693) > > => __do_page_fault (ffffffff810631ea) > > => trace_do_page_fault (ffffffff81063543) > > => do_async_page_fault (ffffffff8105c40a) > > => async_page_fault (ffffffff817581d8) > > [snip] > > <...>-9018 [004] 92.678379: page_ref_mod: pfn=0x17ac9 flags=0x40048 count=2 mapcount=1 mapping=0xffff880015a78dc1 mt=4 val=1 > > [snip] > > ... > > ... > > <...>-9131 [001] 93.174468: test_pages_isolated: start_pfn=0x17800 end_pfn=0x17c00 fin_pfn=0x17ac9 ret=fail > > [snip] > > <...>-9018 [004] 93.174843: page_ref_mod_and_test: pfn=0x17ac9 flags=0x40068 count=0 mapcount=0 mapping=0xffff880015a78dc1 mt=4 val=-1 ret=1 > > => release_pages (ffffffff8117c9e4) > > => free_pages_and_swap_cache (ffffffff811b0697) > > => tlb_flush_mmu_free (ffffffff81199616) > > => tlb_finish_mmu (ffffffff8119a62c) > > => exit_mmap (ffffffff811a53f7) > > => mmput (ffffffff81073f47) > > => do_exit (ffffffff810794e9) > > => do_group_exit (ffffffff81079def) > > => SyS_exit_group (ffffffff81079e74) > > => entry_SYSCALL_64_fastpath (ffffffff817560b6) > > > > This output shows that problem comes from exit path. In exit path, > > to improve performance, pages are not freed immediately. They are gathered > > and processed by batch. During this process, migration cannot be possible > > and CMA allocation is failed. This problem is hard to find without this > > page reference tracepoint facility. > > > > Enabling this feature bloat kernel text 30 KB in my configuration. > > > > text data bss dec hex filename > > 12127327 2243616 1507328 15878271 f2487f vmlinux_disabled > > 12157208 2258880 1507328 15923416 f2f8d8 vmlinux_enabled > > > > v2: > > o Use static key of each tracepoints to avoid function call overhead > > when tracepoints are disabled. > > o Print human-readable page flag through show_page_flags() > > o Add more description to Kconfig.debug. > > > > Acked-by: Michal Nazarewicz <mina86@xxxxxxxxxx> > > Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> > > --- > > include/linux/page_ref.h | 90 +++++++++++++++++++++++++-- > > include/trace/events/page_ref.h | 133 ++++++++++++++++++++++++++++++++++++++++ > > mm/Kconfig.debug | 13 ++++ > > mm/Makefile | 1 + > > mm/debug_page_ref.c | 53 ++++++++++++++++ > > 5 files changed, 285 insertions(+), 5 deletions(-) > > create mode 100644 include/trace/events/page_ref.h > > create mode 100644 mm/debug_page_ref.c > > > > diff --git a/include/linux/page_ref.h b/include/linux/page_ref.h > > index 534249c..fd6d9a5 100644 > > --- a/include/linux/page_ref.h > > +++ b/include/linux/page_ref.h > > @@ -1,6 +1,54 @@ > > #include <linux/atomic.h> > > #include <linux/mm_types.h> > > #include <linux/page-flags.h> > > +#include <linux/tracepoint-defs.h> > > + > > +extern struct tracepoint __tracepoint_page_ref_set; > > +extern struct tracepoint __tracepoint_page_ref_mod; > > +extern struct tracepoint __tracepoint_page_ref_mod_and_test; > > +extern struct tracepoint __tracepoint_page_ref_mod_and_return; > > +extern struct tracepoint __tracepoint_page_ref_mod_unless; > > +extern struct tracepoint __tracepoint_page_ref_freeze; > > +extern struct tracepoint __tracepoint_page_ref_unfreeze; > > + > > +#ifdef CONFIG_DEBUG_PAGE_REF > > +#define page_ref_tracepoint_active(t) static_key_false(&(t).key) > > Please don't open code this. Use the following instead: > > trace_page_ref_set_enabled() > trace_page_ref_mod_enabled() > trace_page_ref_mod_and_test_enabled() > trace_page_ref_mod_and_return_enabled() > trace_page_ref_mod_unless_enabled() > trace_page_ref_freeze_enabled() > trace_page_ref_unfreeze_enabled() > > They return true when CONFIG_TRACEPOINTS is configured in and the > tracepoint is enabled, and false otherwise. This implementation is what you proposed before. Please refer below link and source. https://lkml.org/lkml/2015/12/9/699 arch/x86/include/asm/msr.h There is header file dependency problem between mm.h and tracepoint.h. page_ref.h should be included in mm.h and tracepoint.h cannot be included in this case. Thanks. -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
