linux-kernel - Re: [PATCH v7] mm: slub: move sysfs slab alloc/free interfaces to debugfs

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Date:   Wed, 26 May 2021 13:03:52 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Greg KH <gregkh@...uxfoundation.org>,
        Faiyaz Mohammed <faiyazm@...eaurora.org>
Cc:     cl@...ux.com, penberg@...nel.org, rientjes@...gle.com,
        iamjoonsoo.kim@....com, akpm@...ux-foundation.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        glittao@...il.com, vinmenon@...eaurora.org
Subject: Re: [PATCH v7] mm: slub: move sysfs slab alloc/free interfaces to
 debugfs

On 5/25/21 1:54 PM, Greg KH wrote:
> On Tue, May 25, 2021 at 02:27:15PM +0530, Faiyaz Mohammed wrote:
> >> --- a/mm/slab_common.c
>> >> +++ b/mm/slab_common.c
>> >> @@ -455,6 +455,9 @@ static void slab_caches_to_rcu_destroy_workfn(struct work_struct *work)
>> >>  #else
>> >>  		slab_kmem_cache_release(s);
>> >>  #endif
>> >> +#ifdef SLAB_SUPPORTS_DEBUGFS
>> >> +		debugfs_slab_release(s);
>> >> +#endif
>> > 
>> > Why do you need these #ifdef if your slub_dev.h file already provides an
>> > "empty" function for this?
>> > 
>> We are not including slub_def.h directly. mm/slab.h includes the
>> slub_def.h if CONFIG_SLUB enable,
>> 
>> from mm/slab.h
>> #ifdef CONFIG_SLAB
>> #include <linux/slab_def.h>
>> #endif
>> 
>> #ifdef CONFIG_SLUB
>> #include <linux/slub_def.h>
>> #endif
>> 
>> so if CONFIG_SLAB is enable then mm/slab.h includes slab_def.h, to avoid
>> undefined reference error added SLAB_SUPPORTS_DEBUGFS like
>> SLAB_SUPPORTS_SYSFS.
> 
> Ick, ok, messy code, I'll stop complaining now if this really is the
> only way to do it (still feels wrong to me...)

How about simply replicating the empty function in
include/linux/slab_def.h

We could do the same with SYSFS, except the SLAB (and SLUB w/o SYSFS) versions
of sysfs_slab_release() would not be empty, but just call
slab_kmem_cache_release(s);
Then we could get rid of the #ifdef's completely?

> greg k-h
>