On Mon, Nov 09 2015, Joonsoo Kim wrote: > CMA allocation should be guaranteed to succeed by definition, Uh? That’s a peculiar statement. Which is to say that it’s not true. > 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 20 KB in my configuration. > > text data bss dec hex filename > 12041272 2223424 1507328 15772024 f0a978 vmlinux_disabled > 12064844 2225920 1507328 15798092 f10f4c vmlinux_enabled > > Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> Acked-by: Michal Nazarewicz <mina86@xxxxxxxxxx> > --- > include/trace/events/page_ref.h | 128 ++++++++++++++++++++++++++++++++++++++++ I haven’t really looked at the above file though. -- Best regards, _ _ .o. | Liege of Serenely Enlightened Majesty of o' \,=./ `o ..o | Computer Science, ミハウ “mina86” ナザレヴイツ (o o) ooo +--<mpn@xxxxxxxxxx>--<xmpp:mina86@xxxxxxxxxx>-----ooO--(_)--Ooo-- -- 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
