Re: [PATCH] mm/page_owner: Record timestamp and pid

[Vlastimil Babka]

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@xxxxxxxxxx> 
> > > wrote:
> > >
> > > > From: Liam Mark <lmark@xxxxxxxxxxxxxx>
> > > >
> > > > 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 :)

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 */
> > };