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Date:   Thu, 6 Apr 2023 16:29:57 -0700
From:   Andrew Morton <akpm@linux-foundation.org>
To:     Stefan Roesch <shr@devkernel.io>
Cc:     kernel-team@fb.com, linux-mm@kvack.org, riel@surriel.com,
        mhocko@suse.com, david@redhat.com, linux-kselftest@vger.kernel.org,
        linux-doc@vger.kernel.org, hannes@cmpxchg.org,
        Bagas Sanjaya <bagasdotme@gmail.com>
Subject: Re: [PATCH v5 1/3] mm: add new api to enable ksm per process
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On Thu,  6 Apr 2023 09:53:37 -0700 Stefan Roesch <shr@devkernel.io> wrote:

> So far KSM can only be enabled by calling madvise for memory regions.  To
> be able to use KSM for more workloads, KSM needs to have the ability to be
> enabled / disabled at the process / cgroup level.
> 
> ...
>
> @@ -53,6 +62,18 @@ void folio_migrate_ksm(struct folio *newfolio, struct folio *folio);
>  
>  #else  /* !CONFIG_KSM */
>  
> +static inline int ksm_add_mm(struct mm_struct *mm)
> +{
> +}

The compiler doesn't like the lack of a return value.

I queued up a patch to simply delete the above function - seems that
ksm_add_mm() has no callers if CONFIG_KSM=n.

The same might be true of the ksm_add_vma()...ksm_exit() stubs also,
Perhaps some kind soul could take a look at whether we can simply clean
those out.