On Thu, Feb 4, 2021 at 3:14 PM John Hubbard <jhubbard@xxxxxxxxxx> wrote: > > On 2/4/21 12:07 PM, Minchan Kim wrote: > > On Thu, Feb 04, 2021 at 12:50:58AM -0800, John Hubbard wrote: > >> On 2/3/21 7:50 AM, Minchan Kim wrote: > >>> Since CMA is getting used more widely, it's more important to > >>> keep monitoring CMA statistics for system health since it's > >>> directly related to user experience. > >>> > >>> This patch introduces sysfs for the CMA and exposes stats below > >>> to keep monitor for telemetric in the system. > >>> > >>> * the number of CMA allocation attempts > >>> * the number of CMA allocation failures > >>> * the number of CMA page allocation attempts > >>> * the number of CMA page allocation failures > >> > >> The desire to report CMA data is understandable, but there are a few > >> odd things here: > >> > >> 1) First of all, this has significant overlap with /sys/kernel/debug/cma > >> items. I suspect that all of these items could instead go into > > > > At this moment, I don't see any overlap with item from cma_debugfs. > > Could you specify what item you are mentioning? > > Just the fact that there would be two systems under /sys, both of which are > doing very very similar things: providing information that is intended to > help diagnose CMA. > > > > >> /sys/kernel/debug/cma, right? > > > > Anyway, thing is I need an stable interface for that and need to use > > it in Android production build, too(Unfortunately, Android deprecated > > the debugfs > > https://source.android.com/setup/start/android-11-release#debugfs > > ) > > That's the closest hint to a "why this is needed" that we've seen yet. > But it's only a hint. > > > > > What should be in debugfs and in sysfs? What's the criteria? > > Well, it's a gray area. "Debugging support" goes into debugfs, and > "production-level monitoring and control" goes into sysfs, roughly > speaking. And here you have items that could be classified as either. > > > > > Some statistic could be considered about debugging aid or telemetric > > depening on view point and usecase. And here, I want to use it for > > telemetric, get an stable interface and use it in production build > > of Android. In this chance, I'd like to get concrete guideline > > what should be in sysfs and debugfs so that pointing out this thread > > whenever folks dump their stat into sysfs to avoid waste of time > > for others in future. :) > > > >> > >> 2) The overall CMA allocation attempts/failures (first two items above) seem > >> an odd pair of things to track. Maybe that is what was easy to track, but I'd > >> vote for just omitting them. > > > > Then, how to know how often CMA API failed? > > Why would you even need to know that, *in addition* to knowing specific > page allocation numbers that failed? Again, there is no real-world motivation > cited yet, just "this is good data". Need more stories and support here. IMHO it would be very useful to see whether there are multiple small-order allocation failures or a few large-order ones, especially for CMA where large allocations are not unusual. For that I believe both alloc_pages_attempt and alloc_pages_fail would be required. > > > thanks, > -- > John Hubbard > NVIDIA > > > There are various size allocation request for a CMA so only page > > allocation stat are not enough to know it. > > > >>> > >>> Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx> > >>> --- > >>> Documentation/ABI/testing/sysfs-kernel-mm-cma | 39 +++++ > >>> include/linux/cma.h | 1 + > >>> mm/Makefile | 1 + > >>> mm/cma.c | 6 +- > >>> mm/cma.h | 20 +++ > >>> mm/cma_sysfs.c | 143 ++++++++++++++++++ > >>> 6 files changed, 209 insertions(+), 1 deletion(-) > >>> create mode 100644 Documentation/ABI/testing/sysfs-kernel-mm-cma > >>> create mode 100644 mm/cma_sysfs.c > >>> > >>> diff --git a/Documentation/ABI/testing/sysfs-kernel-mm-cma b/Documentation/ABI/testing/sysfs-kernel-mm-cma > >>> new file mode 100644 > >>> index 000000000000..2a43c0aacc39 > >>> --- /dev/null > >>> +++ b/Documentation/ABI/testing/sysfs-kernel-mm-cma > >>> @@ -0,0 +1,39 @@ > >>> +What: /sys/kernel/mm/cma/ > >>> +Date: Feb 2021 > >>> +Contact: Minchan Kim <minchan@xxxxxxxxxx> > >>> +Description: > >>> + /sys/kernel/mm/cma/ contains a number of subdirectories by > >>> + cma-heap name. The subdirectory contains a number of files > >>> + to represent cma allocation statistics. > >> > >> Somewhere, maybe here, there should be a mention of the closely related > >> /sys/kernel/debug/cma files. > >> > >>> + > >>> + There are number of files under > >>> + /sys/kernel/mm/cma/<cma-heap-name> directory > >>> + > >>> + - cma_alloc_attempt > >>> + - cma_alloc_fail > >> > >> Are these really useful? They a summary of the alloc_pages items, really. > >> > >>> + - alloc_pages_attempt > >>> + - alloc_pages_fail > >> > >> This should also have "cma" in the name, really: cma_alloc_pages_*. > > > > No problem. > > > >> > >>> + > >>> +What: /sys/kernel/mm/cma/<cma-heap-name>/cma_alloc_attempt > >>> +Date: Feb 2021 > >>> +Contact: Minchan Kim <minchan@xxxxxxxxxx> > >>> +Description: > >>> + the number of cma_alloc API attempted > >>> + > >>> +What: /sys/kernel/mm/cma/<cma-heap-name>/cma_alloc_fail > >>> +Date: Feb 2021 > >>> +Contact: Minchan Kim <minchan@xxxxxxxxxx> > >>> +Description: > >>> + the number of CMA_alloc API failed > >>> + > >>> +What: /sys/kernel/mm/cma/<cma-heap-name>/alloc_pages_attempt > >>> +Date: Feb 2021 > >>> +Contact: Minchan Kim <minchan@xxxxxxxxxx> > >>> +Description: > >>> + the number of pages CMA API tried to allocate > >>> + > >>> +What: /sys/kernel/mm/cma/<cma-heap-name>/alloc_pages_fail > >>> +Date: Feb 2021 > >>> +Contact: Minchan Kim <minchan@xxxxxxxxxx> > >>> +Description: > >>> + the number of pages CMA API failed to allocate > >>> diff --git a/include/linux/cma.h b/include/linux/cma.h > >>> index 217999c8a762..71a28a5bb54e 100644 > >>> --- a/include/linux/cma.h > >>> +++ b/include/linux/cma.h > >>> @@ -49,4 +49,5 @@ extern struct page *cma_alloc(struct cma *cma, size_t count, unsigned int align, > >>> extern bool cma_release(struct cma *cma, const struct page *pages, unsigned int count); > >>> extern int cma_for_each_area(int (*it)(struct cma *cma, void *data), void *data); > >>> + > >> > >> A single additional blank line seems to be the only change to this file. :) > > > > Oops. > > >
