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

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Message-ID: <20210927121449.kac5g25aejbwvylf@box>
Date:   Mon, 27 Sep 2021 15:14:49 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Nadav Amit <nadav.amit@...il.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Linux-MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Peter Xu <peterx@...hat.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 Mon, Sep 27, 2021 at 03:31:21AM -0700, Nadav Amit wrote:
> 
> 
> > On Sep 27, 2021, at 2:31 AM, Kirill A. Shutemov <kirill@...temov.name> wrote:
> > 
> > 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.
> 
> I can set another constant instead and let the compiler shout if anything
> outside the array is initialized.

I would rather introduce a function that would return struct madvise_info
for a given behavior. The function would have a switch inside. The default:
may have BUILD_BUG() or something.

-- 
 Kirill A. Shutemov