linux-kernel - Re: [PATCH] mm/khugepaged: add tracepoint to collapse

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Date:   Mon, 24 Oct 2022 23:08:28 +0530
From:   Gautam Menghani <gautammenghani201@...il.com>
To:     Zach O'Keefe <zokeefe@...gle.com>
Cc:     Steven Rostedt <rostedt@...dmis.org>, akpm@...ux-foundation.org,
        mhiramat@...nel.org, shy828301@...il.com, vbabka@...e.cz,
        david@...hat.com, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/khugepaged: add tracepoint to collapse_file()

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.