linux-kernel - Re: [RFC PATCH 4/8] mm/madvise: define madvise behavior in a struct

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Date:   Mon, 27 Sep 2021 12:31:03 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Nadav Amit <nadav.amit@...il.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Peter Xu <peterx@...hat.com>,
        Nadav Amit <namit@...are.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Minchan Kim <minchan@...nel.org>,
        Colin Cross <ccross@...gle.com>,
        Suren Baghdasarya <surenb@...gle.com>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>
Subject: Re: [RFC PATCH 4/8] mm/madvise: define madvise behavior in a struct

On Sun, Sep 26, 2021 at 09:12:55AM -0700, Nadav Amit wrote:
> From: Nadav Amit <namit@...are.com>
> 
> The different behaviors of madvise are different in several ways, which
> are distributed across several functions. Use the design pattern from
> iouring in order to define the actions that are required for each
> behavior.
> 
> The next patches will get rid of old helper functions that are modified
> in this patch and the redundant use of array_index_nospec(). The next
> patches will add more actions for each leaf into the new struct.
> 
> No functional change is intended.
> 
> Cc: Andrea Arcangeli <aarcange@...hat.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Minchan Kim <minchan@...nel.org>
> Cc: Colin Cross <ccross@...gle.com>
> Cc: Suren Baghdasarya <surenb@...gle.com>
> Cc: Mike Rapoport <rppt@...ux.vnet.ibm.com>
> Signed-off-by: Nadav Amit <namit@...are.com>
> ---
>  mm/madvise.c | 168 +++++++++++++++++++++++++++++++++------------------
>  1 file changed, 109 insertions(+), 59 deletions(-)
> 
> diff --git a/mm/madvise.c b/mm/madvise.c
> index 17e39c70704b..127507c71ba9 100644
> --- a/mm/madvise.c
> +++ b/mm/madvise.c
> @@ -29,6 +29,7 @@
>  #include <linux/swapops.h>
>  #include <linux/shmem_fs.h>
>  #include <linux/mmu_notifier.h>
> +#include <linux/nospec.h>
>  
>  #include <asm/tlb.h>
>  
> @@ -39,6 +40,101 @@ struct madvise_walk_private {
>  	bool pageout;
>  };
>  
> +struct madvise_info {
> +	u8 behavior_valid: 1;
> +	u8 process_behavior_valid: 1;
> +	u8 need_mmap_read_only: 1;
> +};
> +
> +static const struct madvise_info madvise_info[MADV_SOFT_OFFLINE+1] = {

MADV_SOFT_OFFLINE+1 smells bad.

And I don't like the change in general. Given that MADV_SOFT_OFFLINE is
101, the array will be mostly empty.

I donno. I don't see any improvement with the patch. But maybe it's only me.

-- 
 Kirill A. Shutemov