linux-kernel - Re: [RFC PATCH] mm/slub: enable debugging memory wasting of kmalloc

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Message-ID: <CAB=+i9RhuAi-w3XbXO5236WFeg04A6ra_xG9o_-DkMaRBFMKGw@mail.gmail.com>
Date:   Thu, 30 Jun 2022 23:55:59 +0900
From:   Hyeonggon Yoo <42.hyeyoo@...il.com>
To:     Feng Tang <feng.tang@...el.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Linux Memory Management List <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Dave Hansen <dave.hansen@...el.com>
Subject: Re: [RFC PATCH] mm/slub: enable debugging memory wasting of kmalloc

On Thu, Jun 30, 2022 at 11:38 PM Hyeonggon Yoo <42.hyeyoo@...il.com> wrote:
[...]
> > @@ -5138,11 +5146,12 @@ static int add_location(struct loc_track *t, struct kmem_cache *s,
> >               if (pos == end)
> >                       break;
> >
> > -             caddr = t->loc[pos].addr;
> > -             chandle = t->loc[pos].handle;
> > -             if ((track->addr == caddr) && (handle == chandle)) {
> > +             l = &t->loc[pos];
> > +             caddr = l->addr;
> > +             chandle = l->handle;
> > +             if ((track->addr == caddr) && (handle == chandle) &&
> > +                     (track->waste == l->waste)) {
> >
> > -                     l = &t->loc[pos];
> >                       l->count++;
> >                       if (track->when) {
> >                               l->sum_time += age;
> > @@ -5190,6 +5199,7 @@ static int add_location(struct loc_track *t, struct kmem_cache *s,
> >       l->min_pid = track->pid;
> >       l->max_pid = track->pid;
> >       l->handle = handle;
> > +     l->waste = track->waste;
>
> I think this may be fooled when there are different wastes values
> from same caller (i.e. when a kmalloc_track_caller() is used.)
> because the array is sorted by caller address, but not sorted by waste.
>
> And writing this I noticed that it already can be fooled now :)
> It's also not sorted by handle.

I misread the code. it's not fooled now. the array is also sorted by handle.
But will be fooled after this patch.

> --
> Thanks,
> Hyeonggon