linux-kernel - Re: [PATCH v4 1/2] mm/memory-failure.c clean up around tk pre-allocation

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Date:   Tue, 6 Aug 2019 14:05:25 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Jane Chu <jane.chu@...cle.com>
Cc:     Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
        Linux MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-nvdimm <linux-nvdimm@...ts.01.org>
Subject: Re: [PATCH v4 1/2] mm/memory-failure.c clean up around tk pre-allocation

Hi Jane, looks good. Checkpatch prompts me to point out a couple more fixups:

This patch is titled:

    "mm/memory-failure.c clean up..."

...to match the second patch it should be:

    "mm/memory-failure: clean up..."

On Tue, Aug 6, 2019 at 10:26 AM Jane Chu <jane.chu@...cle.com> wrote:
>
> add_to_kill() expects the first 'tk' to be pre-allocated, it makes
> subsequent allocations on need basis, this makes the code a bit
> difficult to read. Move all the allocation internal to add_to_kill()
> and drop the **tk argument.
>
> Signed-off-by: Jane Chu <jane.chu@...cle.com>
> ---
>  mm/memory-failure.c | 40 +++++++++++++---------------------------
>  1 file changed, 13 insertions(+), 27 deletions(-)
>
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index d9cc660..51d5b20 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -304,25 +304,19 @@ static unsigned long dev_pagemap_mapping_shift(struct page *page,
>  /*
>   * Schedule a process for later kill.
>   * Uses GFP_ATOMIC allocations to avoid potential recursions in the VM.
> - * TBD would GFP_NOIO be enough?
>   */
>  static void add_to_kill(struct task_struct *tsk, struct page *p,
>                        struct vm_area_struct *vma,
> -                      struct list_head *to_kill,
> -                      struct to_kill **tkc)
> +                      struct list_head *to_kill)
>  {
>         struct to_kill *tk;
>
> -       if (*tkc) {
> -               tk = *tkc;
> -               *tkc = NULL;
> -       } else {
> -               tk = kmalloc(sizeof(struct to_kill), GFP_ATOMIC);
> -               if (!tk) {
> -                       pr_err("Memory failure: Out of memory while machine check handling\n");
> -                       return;
> -               }
> +       tk = kmalloc(sizeof(struct to_kill), GFP_ATOMIC);
> +       if (!tk) {
> +               pr_err("Memory failure: Out of memory while machine check handling\n");
> +               return;
>         }

checkpatch points out that this error message can be deleted.
According to the commit that added this check (ebfdc40969f2
"checkpatch: attempt to find unnecessary 'out of memory' messages")
the kernel already prints a message and a backtrace on these events,
so seems like a decent additional cleanup to fold.

With those fixups you can add:

Reviewed-by: Dan Williams <dan.j.williams@...el.com>

...along with Naoya's ack.

I would Cc: Andrew Morton on the v5 posting of these as he's the
upstream path for changes to this file.