[ltt-dev] No page alloc events

[ltt-dev] No page alloc events

[Francis Giraldeau]

Hi, 

I got a really strange behavior with mm events. When the process exits,
there are a bunch of mm.page_free that occurs, but mm.page_alloc never
occur before them which is weird. I was expecting the number of
page_free to equal the number of page_alloc, only page_free fires.

If I understand correctly, if a program does a malloc, libc internally
calls sys_brk and heap is increased. But, physical memory pages are only
allocated by the page fault handler when they are accessed. So, I should
have seen the page_alloc when writing or reading the memory, isn't?
Well, page fauts are present, but then again, no page_alloc.

The trace_page_alloc tracepoint is in __alloc_pages_slowpath, and is
normally called by __do_fault. It seems that this is never called, so
maybe the tracepoint should belong to another function?

Using kernel 2.6.38.6-lttng-0.249 and lttng-modules v0.19-stable. 

Have a nice day, 

Francis