2016-03-03 1:58 GMT+09:00 Vlastimil Babka <vbabka@xxxxxxx>: > On 02/26/2016 01:58 AM, 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. (note: this example is >> stale version that printing flags as the number. Recent version will >> print it as human readable string.) >> >> 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 >> > > That's not bad, and it's even configurable. Thanks for taking the extra care > about overhead since v1. > >> 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 >> >> v3: >> o Add commit description and code comment why this patch open code >> the static key functions for tracepoints. >> o Notify that example is stale version. >> o Add "depends on TRACEPOINTS". >> >> v2: >> o Use static key of each tracepoints to avoid function call overhead >> when tracepoints are disabled. >> o Print human-readable page flag thanks to newly introduced %pgp option. >> o Add more description to Kconfig.debug. >> >> Acked-by: Michal Nazarewicz <mina86@xxxxxxxxxx> >> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> > > > Acked-by: Vlastimil Babka <vbabka@xxxxxxx> > >> +config DEBUG_PAGE_REF >> + bool "Enable tracepoint to track down page reference manipulation" >> + depends on DEBUG_KERNEL >> + depends on TRACEPOINTS >> + ---help--- >> + This is the feature to add tracepoint for tracking down page >> reference >> + manipulation. This tracking is useful to diagnosis functional >> failure >> + due to migration failure caused by page reference mismatch. Be > > > OK. > >> + careful to turn on this feature because it could bloat some >> kernel >> + text. In my configuration, it bloats 30 KB. Although kernel text >> will >> + be bloated, there would be no runtime performance overhead if >> + tracepoint isn't enabled thanks to jump label. > > > I would just write something like: > > Enabling this feature adds about 30 KB to the kernel code, but runtime > performance overhead is virtually none until the tracepoints are actually > enabled. Okay, better! Andrew, do you want fixup patch from me or could you simply handle it? Thanks. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>