Re: [PATCH] mm/khugepaged: add tracepoint to collapse_file()

From: Steven Rostedt
Date: Mon Oct 24 2022 - 12:56:24 EST


On Mon, 24 Oct 2022 20:39:22 +0530
Gautam Menghani <gautammenghani201@xxxxxxxxx> wrote:

> +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>
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index 4734315f7940..14db90e2f2ec 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -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,

I try to keep dereferences out of the calling path as much as possible
(adds to I$ at the call site).

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;