Messages in this thread | | | Date | Wed, 31 Dec 2014 09:58:04 +0900 | From | Gioh Kim <> | Subject | Re: [PATCH 0/3] mm: cma: /proc/cmainfo |
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2014-12-30 오후 1:47에 Minchan Kim 이(가) 쓴 글: > On Mon, Dec 29, 2014 at 11:52:58AM -0800, Laura Abbott wrote: >> On 12/28/2014 6:36 PM, Minchan Kim wrote: >>> Hello, >>> >>> On Fri, Dec 26, 2014 at 05:39:01PM +0300, Stefan I. Strogin wrote: >>>> Hello all, >>>> >>>> Here is a patch set that adds /proc/cmainfo. >>>> >>>> When compiled with CONFIG_CMA_DEBUG /proc/cmainfo will contain information >>>> about about total, used, maximum free contiguous chunk and all currently >>>> allocated contiguous buffers in CMA regions. The information about allocated >>>> CMA buffers includes pid, comm, allocation latency and stacktrace at the >>>> moment of allocation. >>> >>> It just says what you are doing but you didn't say why we need it. >>> I can guess but clear description(ie, the problem what you want to >>> solve with this patchset) would help others to review, for instance, >>> why we need latency, why we need callstack, why we need new wheel >>> rather than ftrace and so on. >>> >>> Thanks. >>> >> >> >> I've been meaning to write something like this for a while so I'm >> happy to see an attempt made to fix this. I can't speak for the >> author's reasons for wanting this information but there are >> several reasons why I was thinking of something similar. >> >> The most common bug reports seen internally on CMA are 1) CMA is >> too slow and 2) CMA failed to allocate memory. For #1, not all >> allocations may be slow so it's useful to be able to keep track >> of which allocations are taking too long. For #2, migration > > Then, I don't think we could keep all of allocations. What we need > is only slow allocations. I hope we can do that with ftrace. > > ex) > > # cd /sys/kernel/debug/tracing > # echo 1 > options/stacktrace > # echo cam_alloc > set_ftrace_filter > # echo your_threshold > tracing_thresh > > I know it doesn't work now but I think it's more flexible > and general way to handle such issues(ie, latency of some functions). > So, I hope we could enhance ftrace rather than new wheel. > Ccing ftrace people.
For CMA performance test or code flow check, ftrace is better.
ex) echo cma_alloc > /sys/kernel/debug/tracing/set_graph_function echo function_graph > /sys/kernel/debug/tracing/current_tracer echo funcgraph-proc > /sys/kernel/debug/tracing/trace_options echo nosleep-time > /sys/kernel/debug/tracing/trace_options echo funcgraph-tail > /sys/kernel/debug/tracing/trace_options echo 1 > /sys/kernel/debug/tracing/tracing_on
This can trace every cam_alloc and allocation time. I think ftrace is better to debug latency. If a buffer had allocated and had peak latency and freed, we can check it.
But ftrace doesn't provide current status how many buffers we have and what address it is. So I think debugging information is useful.
> > Futhermore, if we really need to have such information, we need more data > (ex, how many of pages were migrated out, how many pages were dropped > without migrated, how many pages were written back, how many pages were > retried with the page lock and so on). > In this case, event trace would be better. > > >> failure is fairly common but it's still important to rule out >> a memory leak from a dma client. Seeing all the allocations is >> also very useful for memory tuning (e.g. how big does the CMA >> region need to be, which clients are actually allocating memory). > > Memory leak is really general problem and could we handle it with > page_owner? > >> >> ftrace is certainly usable for tracing CMA allocation callers and >> latency. ftrace is still only a fixed size buffer though so it's >> possible for information to be lost if other logging is enabled. > > Sorry, I don't get with only above reasons why we need this. :( > >> For most of the CMA use cases, there is a very high cost if the >> proper debugging information is not available so the more that >> can be guaranteed the better. >> >> It's also worth noting that the SLUB allocator has a sysfs >> interface for showing allocation callers when CONFIG_SLUB_DEBUG >> is enabled. >> >> Thanks, >> Laura >> >> -- >> Qualcomm Innovation Center, Inc. >> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, >> a Linux Foundation Collaborative Project >> >> -- >> To unsubscribe, send a message with 'unsubscribe linux-mm' in >> the body to majordomo@kvack.org. For more info on Linux MM, >> see: http://www.linux-mm.org/ . >> Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a> >
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