linux-kernel - Re: [PATCH v1] mm/slub: enable debugging memory wasting of kmalloc

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Message-ID: <20220701150451.GA62281@shbuild999.sh.intel.com>
Date:   Fri, 1 Jul 2022 23:04:51 +0800
From:   Feng Tang <feng.tang@...el.com>
To:     Christoph Lameter <cl@...two.de>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        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>,
        Hyeonggon Yoo <42.hyeyoo@...il.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, dave.hansen@...el.com,
        Robin Murphy <robin.murphy@....com>,
        John Garry <john.garry@...wei.com>
Subject: Re: [PATCH v1] mm/slub: enable debugging memory wasting of kmalloc

Hi Christoph,

On Fri, Jul 01, 2022 at 04:37:00PM +0200, Christoph Lameter wrote:
> On Fri, 1 Jul 2022, Feng Tang wrote:
> 
> >  static void *__slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
> > -			  unsigned long addr, struct kmem_cache_cpu *c)
> > +			  unsigned long addr, struct kmem_cache_cpu *c, unsigned int orig_size)
> >  {
> 
> It would be good to avoid expanding the basic slab handling functions for
> kmalloc. Can we restrict the mods to the kmalloc related functions?

Yes, this is the part that concerned me. I tried but haven't figured
a way.

I started implemting it several month ago, and stuck with several
kmalloc APIs in a hacky way like dump_stack() when there is a waste
over 1/4 of the object_size of the kmalloc_caches[][].

Then I found one central API which has all the needed info (object_size &
orig_size) that we can yell about the waste :

static __always_inline void *slab_alloc_node(struct kmem_cache *s, struct list_lru *lru,
                gfp_t gfpflags, int node, unsigned long addr, size_t orig_size)

which I thought could be still hacky, as the existing 'alloc_traces'
can't be resued which already has the count/call-stack info. Current
solution leverage it at the cost of adding 'orig_size' parameters, but
I don't know how to pass the 'waste' info through as track/location is
in the lowest level.

Thanks,
Feng