mm/khugepaged: add tracepoint to collapse_file()
Commit Message
In the file mm/khugepaged.c, a TODO in the function collapse_file() asks
to add tracepoints. Add the tracepoint named "mm_khugepaged_scan_file".
Signed-off-by: Gautam Menghani <gautammenghani201@gmail.com>
---
include/trace/events/huge_memory.h | 32 ++++++++++++++++++++++++++++++
mm/khugepaged.c | 4 +++-
2 files changed, 35 insertions(+), 1 deletion(-)
Comments
Thanks for your mail, Gautam.
> I try to keep dereferences out of the calling path as much as possible
> (adds to I$ at the call site).
This was probably due to the way I handled
trace_mm_khugepaged_scan_file(). Perhaps that can be cleaned up at the
same time as this patch, for consistency.
Also, no qualms about adding this tracepoint; there are a few scan
result codes that overlap between hpage_collapse_scan_file() and those
possibly returned in collapse_file() such that, if we only have the
one tracepoint in hpage_collapse_scan_file(), it could be ambiguous
what callsite the error path stemmed from. Luckily this hasn't been an
issue thus far.
Lastly, a few other items we might care about capturing:
- is_shmem (perhaps the filename is enough to know this - but I know
at least once during development I was caught off-guard b/c a mount I
thought to be file-backed turned out to be tmpfs (and something I
didn't think to question until I had wasted some time on other
paths)).
- index
Best,
Zach
> Could you just pass in file, and then have:
>
> __string(filename, file->f_path.dentry->d_iname)
>
> [..]
>
> __assign_string(filename, file->f_path.dentry->d_iname);
>
>
> If you are paranoid, you can have the above also be:
>
> file ? file->f_path.dentry ? file->f_path.dentry->d_iname : "(null)" : "(null)")
>
>
> -- Steve
>
>
> > + nr, result);
> > return result;
On Mon, Oct 24, 2022 at 09:44:16AM -0700, Zach O'Keefe wrote:
> Thanks for your mail, Gautam.
>
> > I try to keep dereferences out of the calling path as much as possible
> > (adds to I$ at the call site).
>
> This was probably due to the way I handled
> trace_mm_khugepaged_scan_file(). Perhaps that can be cleaned up at the
> same time as this patch, for consistency.
>
Yes sure I'll send a patch for cleaning this up.
> Also, no qualms about adding this tracepoint; there are a few scan
> result codes that overlap between hpage_collapse_scan_file() and those
> possibly returned in collapse_file() such that, if we only have the
> one tracepoint in hpage_collapse_scan_file(), it could be ambiguous
> what callsite the error path stemmed from. Luckily this hasn't been an
> issue thus far.
>
> Lastly, a few other items we might care about capturing:
>
> - is_shmem (perhaps the filename is enough to know this - but I know
> at least once during development I was caught off-guard b/c a mount I
> thought to be file-backed turned out to be tmpfs (and something I
> didn't think to question until I had wasted some time on other
> paths)).
> - index
Yes noted.
@@ -203,5 +203,37 @@ TRACE_EVENT(mm_khugepaged_scan_file,
__print_symbolic(__entry->result, SCAN_STATUS))
);
+TRACE_EVENT(mm_khugepaged_collapse_file,
+ TP_PROTO(struct mm_struct *mm, struct page *hpage,
+ unsigned long addr, const char *filename, int nr,
+ int result),
+ TP_ARGS(mm, hpage, addr, filename, nr, result),
+ TP_STRUCT__entry(
+ __field(struct mm_struct *, mm)
+ __field(unsigned long, hpfn)
+ __field(unsigned long, addr)
+ __string(filename, filename)
+ __field(int, nr)
+ __field(int, result)
+ ),
+
+ TP_fast_assign(
+ __entry->mm = mm;
+ __entry->hpfn = hpage ? page_to_pfn(hpage) : -1;
+ __entry->addr = addr;
+ __assign_str(filename, filename);
+ __entry->nr = nr;
+ __entry->result = result;
+ ),
+
+ TP_printk("mm=%p, hpage_pfn=0x%lx, addr=%ld, filename=%s, nr=%d, result=%s",
+ __entry->mm,
+ __entry->hpfn,
+ __entry->addr,
+ __get_str(filename),
+ __entry->nr,
+ __print_symbolic(__entry->result, SCAN_STATUS))
+);
+
#endif /* __HUGE_MEMORY_H */
#include <trace/define_trace.h>
@@ -2059,7 +2059,9 @@ static int collapse_file(struct mm_struct *mm, unsigned long addr,
mem_cgroup_uncharge(page_folio(hpage));
put_page(hpage);
}
- /* TODO: tracepoints */
+
+ trace_mm_khugepaged_collapse_file(mm, hpage, addr, file->f_path.dentry->d_iname,
+ nr, result);
return result;
}