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

[Vlastimil Babka]

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:

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 */
};


> Are there userspace tools which aid in the processing of this new
> information?
>
> Can/should Documentation/vm/page_owner.rst be updated?
>
> > --- a/mm/page_owner.c
> > +++ b/mm/page_owner.c
> > @@ -10,6 +10,7 @@
> >  #include <linux/migrate.h>
> >  #include <linux/stackdepot.h>
> >  #include <linux/seq_file.h>
> > +#include <linux/sched/clock.h>
> >  
> >  #include "internal.h"
> >  
> > @@ -25,6 +26,8 @@ struct page_owner {
> >  	gfp_t gfp_mask;
> >  	depot_stack_handle_t handle;
> >  	depot_stack_handle_t free_handle;
> > +	u64 ts_nsec;
> > +	int pid;
>
> pid_t would be nicer?