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

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Date:   Tue, 25 May 2021 13:54:49 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Faiyaz Mohammed <faiyazm@...eaurora.org>
Cc:     cl@...ux.com, penberg@...nel.org, rientjes@...gle.com,
        iamjoonsoo.kim@....com, akpm@...ux-foundation.org, vbabka@...e.cz,
        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 Tue, May 25, 2021 at 02:27:15PM +0530, Faiyaz Mohammed wrote:
> 
> 
> On 5/25/2021 1:23 PM, Greg KH wrote:
> > On Tue, May 25, 2021 at 01:08:05PM +0530, Faiyaz Mohammed wrote:
> >> alloc_calls and free_calls implementation in sysfs have two issues,
> >> one is PAGE_SIZE limitiation of sysfs and other is it does not adhere
> >> to "one value per file" rule.
> >>
> >> To overcome this issues, move the alloc_calls and free_calls implemeation
> >> to debugfs.
> >>
> >> Rename the alloc_calls/free_calls to alloc_traces/free_traces,
> >> to be inline with what it does.
> >>
> >> Reported-by: kernel test robot <lkp@...el.com>
> >> Reported-by: Dan Carpenter <dan.carpenter@...cle.com>
> >> Signed-off-by: Faiyaz Mohammed <faiyazm@...eaurora.org>
> >> ---
> >> changes in V7:
> >>         - Drop the older alloc_calls and free_calls interface.
> >> changes in v6:
> >>         - https://lore.kernel.org/linux-mm/1621341949-26762-1-git-send-email-faiyazm@codeaurora.org/
> >>
> >> changes in v5:
> >>         - https://lore.kernel.org/linux-mm/1620296523-21922-1-git-send-email-faiyazm@codeaurora.org/
> >>
> >> changes in v4:
> >>         - https://lore.kernel.org/linux-mm/1618583239-18124-1-git-send-email-faiyazm@codeaurora.org/
> >>
> >> changes in v3:
> >>         - https://lore.kernel.org/linux-mm/1617712064-12264-1-git-send-email-faiyazm@codeaurora.org/
> >>
> >> changes in v2:
> >>         - https://lore.kernel.org/linux-mm/3ac1d3e6-6207-96ad-16a1-0f5139d8b2b5@codeaurora.org/
> >>
> >> changes in v1:
> >>         - https://lore.kernel.org/linux-mm/1610443287-23933-1-git-send-email-faiyazm@codeaurora.org/
> >>
> >>  include/linux/slub_def.h |   8 ++
> >>  mm/slab_common.c         |   9 ++
> >>  mm/slub.c                | 353 ++++++++++++++++++++++++++++++++++-------------
> >>  3 files changed, 276 insertions(+), 94 deletions(-)
> >>
> >> diff --git a/include/linux/slub_def.h b/include/linux/slub_def.h
> >> index dcde82a..b413ebe 100644
> >> --- a/include/linux/slub_def.h
> >> +++ b/include/linux/slub_def.h
> >> @@ -159,6 +159,14 @@ static inline void sysfs_slab_release(struct kmem_cache *s)
> >>  }
> >>  #endif
> >>  
> >> +#if defined(CONFIG_DEBUG_FS) && defined(CONFIG_SLUB_DEBUG)
> >> +#define SLAB_SUPPORTS_DEBUGFS
> >> +void debugfs_slab_release(struct kmem_cache *);
> >> +#else
> >> +static inline void debugfs_slab_release(struct kmem_cache *s)
> >> +{
> >> +}
> >> +#endif
> >>  void object_err(struct kmem_cache *s, struct page *page,
> >>  		u8 *object, char *reason);
> >>  
> >> diff --git a/mm/slab_common.c b/mm/slab_common.c
> >> index a4a5714..873dd79 100644
> >> --- 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...)

greg k-h