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Subject: Re: [PATCH v7] mm: slub: move sysfs slab alloc/free interfaces to
 debugfs
To:     Vlastimil Babka <vbabka@suse.cz>, cl@linux.com, penberg@kernel.org,
        rientjes@google.com, iamjoonsoo.kim@lge.com,
        akpm@linux-foundation.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, greg@kroah.com, glittao@gmail.com
Cc:     vinmenon@codeaurora.org
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From:   Faiyaz Mohammed <faiyazm@codeaurora.org>
Message-ID: <d53ca307-49a7-9999-f3d1-b8c03ab25773@codeaurora.org>
Date:   Mon, 31 May 2021 16:37:47 +0530
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On 5/31/2021 3:25 PM, Vlastimil Babka wrote:
> On 5/31/21 8:55 AM, Faiyaz Mohammed wrote:
> 
>>> I don't see any of the symlinks under /sys/kernel/debug/slab/, so I think the
>>> aliases handling code is wrong, and I can see at least two reasons why it could be:
>>>
>>
>> I think I missed one thing, when CONFIG_SLUB_DEBUG_ON enable or
>> slub_debug is pass through command line __kmem_cache_alias() will return
>> null, so no symlinks will be created even if CONFIG_SLAB_MERGE_DEFAULT
>> is enable and to store user data we need to enable CONFIG_SLUB_DEBUG_ON
>> or pass slub_debug through command line.
> 
> So you're saying that caches with SLAB_STORE_USER can never be aliases as the
> merging logic will prevent merging with any debug flag, including STORE_USER. So
> if we ignore aliases, it means we will not create the debugfs files for caches,
> where opening the files would just return error, so we don't lose anything by
> not creating the files in the first place.
> 
> In that case, for consistency I would recommend to skip debugfs creation for all
> caches without SLAB_STORE_USER (even if the caches are not an alias). I think we
> can make this decision now as it's a whole new debugfs subtree so we don't break
> any pre-existing code.
> 

Hmmm, I think yes we can skip debugfs creation for all cache without
SLAB_STORE_USER	flag set instead of returning error after opening of
file. I will do the change in next patch version.

Thanks and regards,
Mohammed Faiyaz