From 95813b8faa0cd315f61a8b9d9c523792370b693e Mon Sep 17 00:00:00 2001 From: Joonsoo Kim Date: Thu, 17 Mar 2016 14:19:29 -0700 Subject: mm/page_ref: add tracepoint to track down page reference manipulation 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. (note: this example is stale version that printing flags as the number. Recent version will print it as human readable string.) <...>-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 Note that, due to header file dependency problem between mm.h and tracepoint.h, this feature has to open code the static key functions for tracepoints. Proposed by Steven Rostedt in following link. https://lkml.org/lkml/2015/12/9/699 [arnd@arndb.de: crypto/async_pq: use __free_page() instead of put_page()] [iamjoonsoo.kim@lge.com: fix build failure for xtensa] [akpm@linux-foundation.org: tweak Kconfig text, per Vlastimil] Signed-off-by: Joonsoo Kim Acked-by: Michal Nazarewicz Acked-by: Vlastimil Babka Cc: Minchan Kim Cc: Mel Gorman Cc: "Kirill A. Shutemov" Cc: Sergey Senozhatsky Acked-by: Steven Rostedt Signed-off-by: Arnd Bergmann Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- crypto/async_tx/async_pq.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'crypto/async_tx') diff --git a/crypto/async_tx/async_pq.c b/crypto/async_tx/async_pq.c index c0748bbd4c08..08b3ac68952b 100644 --- a/crypto/async_tx/async_pq.c +++ b/crypto/async_tx/async_pq.c @@ -444,7 +444,7 @@ static int __init async_pq_init(void) static void __exit async_pq_exit(void) { - put_page(pq_scribble_page); + __free_page(pq_scribble_page); } module_init(async_pq_init); -- cgit v1.2.3