linux-kernel - Re: [PATCH for-mm 1/2 v2] mm/internal: Implement no-op mlock_page_drain() for !CONFIG

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Date:   Thu, 10 Feb 2022 07:58:24 +0000
From:   SeongJae Park <sj@...nel.org>
To:     Hugh Dickins <hughd@...gle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        SeongJae Park <sj@...nel.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Naresh Kamboju <naresh.kamboju@...aro.org>,
        Linux MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH for-mm 1/2 v2] mm/internal: Implement no-op mlock_page_drain() for !CONFIG_MMU

On Wed, 9 Feb 2022 20:44:02 -0800 (PST) Hugh Dickins <hughd@...gle.com> wrote:

> From: SeongJae Park <sj@...nel.org>
> 
> Commit 4b3b8bd6c8287 ("mm/munlock: mlock_page() munlock_page() batch by
> pagevec") in -mm tree[1] implements 'mlock_page_drain()' under
> CONFIG_MMU only, but the function is used by 'lru_add_drain_cpu()',
> which defined outside of CONFIG_MMU.  As a result, below build error
> occurs.
> 
>     /linux/mm/swap.c: In function 'lru_add_drain_cpu':
>     /linux/mm/swap.c:637:2: error: implicit declaration of function 'mlock_page_drain' [-Werror=implicit-function-declaration]
>       637 |  mlock_page_drain(cpu);
>           |  ^~~~~~~~~~~~~~~~
>     cc1: some warnings being treated as errors
>     /linux/scripts/Makefile.build:289: recipe for target 'mm/swap.o' failed
> 
> This commit fixes it by implementing no-op 'mlock_page_drain()' for
> !CONFIG_MMU case, similar to 'mlock_new_page()'.
> 
> [1] https://www.ozlabs.org/~akpm/mmotm/broken-out/mm-munlock-mlock_page-munlock_page-batch-by-pagevec.patch
> 
> [hughd: add need_mlock_page_drain() stub too]
> Signed-off-by: SeongJae Park <sj@...nel.org>
> Signed-off-by: Hugh Dickins <hughd@...gle.com>
> ---
> Andrew, Stephen, please add as fix to
> mm-munlock-mlock_page-munlock_page-batch-by-pagevec.patch
> Thanks!

Thank you, Hugh!


Thanks,
SJ

> 
>  mm/internal.h |    2 ++
>  1 file changed, 2 insertions(+)
> 
> --- a/mm/internal.h
> +++ b/mm/internal.h
> @@ -508,6 +508,8 @@ static inline void mlock_vma_page(struct page *page,
>  static inline void munlock_vma_page(struct page *page,
>  			struct vm_area_struct *vma, bool compound) { }
>  static inline void mlock_new_page(struct page *page) { }
> +static inline bool need_mlock_page_drain(int cpu) { return false; }
> +static inline void mlock_page_drain(int cpu) { }
>  static inline void vunmap_range_noflush(unsigned long start, unsigned long end)
>  {
>  }
>