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From:   Souptick Joarder <jrdr.linux@gmail.com>
Date:   Sat, 28 Nov 2020 00:53:11 +0530
Message-ID: <CAFqt6zaZ8NCUUMpXA_-r2D-c_J99yrhjfRrpPFYhcebASeHebw@mail.gmail.com>
Subject: Re: [PATCH] mm/page_owner: Record timestamp and pid
To:     Vlastimil Babka <vbabka@suse.cz>
Cc:     Georgi Djakov <georgi.djakov@linaro.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linux-MM <linux-mm@kvack.org>, linux-kernel@vger.kernel.org,
        sudaraja@codeaurora.org, pratikp@codeaurora.org,
        lmark@codeaurora.org
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On Sat, Nov 28, 2020 at 12:36 AM Vlastimil Babka <vbabka@suse.cz> wrote:
>
> On 11/27/20 7:57 PM, Georgi Djakov wrote:
> > Hi Vlastimil,
> >
> > Thanks for the comment!
> >
> > On 11/27/20 19:52, Vlastimil Babka wrote:
> >> On 11/12/20 8:14 PM, Andrew Morton wrote:
> >>> On Thu, 12 Nov 2020 20:41:06 +0200 Georgi Djakov <georgi.djakov@linaro.org>
> >>> wrote:
> >>>
> >>>> From: Liam Mark <lmark@codeaurora.org>
> >>>>
> >>>> Collect the time for each allocation recorded in page owner so that
> >>>> allocation "surges" can be measured.
> >>>>
> >>>> Record the pid for each allocation recorded in page owner so that
> >>>> the source of allocation "surges" can be better identified.
> >>>
> >>> Please provide a description of why this is considered useful.  What
> >>> has it been used for, what problems has it been used to solve?
> >>
> >> Worth noting that on x86_64 it doubles the size of struct page_owner
> >> from 16 bytes to 32, so it better be justified:
> >
> > Well, that's true. But for debug options there is almost always some penalty.
> > The timestamp and pid information is very useful for me (and others, i believe)
> > when doing memory analysis. On a crash for example, we can get this information
> > from kdump (or RAM-dump) and look into it to catch memory allocation problems
> > more easily.
>
> Right. Btw, you should add printing the info to __dump_page_owner().
>
> > If you find the above argument not strong enough, how about a separate config
> > option for this? Maybe something like CONFIG_PAGE_OWNER_EXTENDED, which could
> > be enabled in addition to CONFIG_PAGE_OWNER?
>
> It might be strong enough if it's mentioned in changelog, and also what exactly
> the space tradeoff is :)

Just a thought ... putting it inside CONFIG_PAGE_OWNER_DEBUG might be
better if it is used
purely for debugging purposes.

>
> You can also mention that SLUB object tracking has also pid+timestamp.
>
> > Thanks,
> > Georgi
> >
> >>
> >> struct page_owner {
> >>          short unsigned int         order;                /*     0     2 */
> >>          short int                  last_migrate_reason;  /*     2     2 */
> >>          gfp_t                      gfp_mask;             /*     4     4 */
> >>          depot_stack_handle_t       handle;               /*     8     4 */
> >>          depot_stack_handle_t       free_handle;          /*    12     4 */
> >>          u64                        ts_nsec;              /*    16     8 */
> >>          int                        pid;                  /*    24     4 */
> >>
> >>          /* size: 32, cachelines: 1, members: 7 */
> >>          /* padding: 4 */
> >>          /* last cacheline: 32 bytes */
> >> };
> >>
> >
>
>