linux-kernel - Re: [PATCH] ipc/shm.c add ->pagesize function to shm_vm

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Date:   Sat, 28 Jul 2018 12:02:48 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Jane Chu <jane.chu@...cle.com>
Cc:     akpm@...ux-foundation.org, dan.j.williams@...el.com,
        mhocko@...e.com, jack@...e.cz, jglisse@...hat.com,
        mike.kravetz@...cle.com, dave@...olabs.net, linux-mm@...ck.org,
        linux-nvdimm@...ts.01.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ipc/shm.c add ->pagesize function to shm_vm_ops

On Fri, Jul 27, 2018 at 03:17:27PM -0600, Jane Chu wrote:
> +++ b/include/linux/mm.h
> @@ -387,6 +387,13 @@ enum page_entry_size {
>   * These are the virtual MM functions - opening of an area, closing and
>   * unmapping it (needed to keep files on disk up-to-date etc), pointer
>   * to the functions called when a no-page or a wp-page exception occurs.
> + *
> + * Note, when a new function is introduced to vm_operations_struct and
> + * added to hugetlb_vm_ops, please consider adding the function to
> + * shm_vm_ops. This is because under System V memory model, though
> + * mappings created via shmget/shmat with "huge page" specified are
> + * backed by hugetlbfs files, their original vm_ops are overwritten with
> + * shm_vm_ops.
>   */
>  struct vm_operations_struct {

I don't think this header file is the right place for this comment.
I'd think a better place for it would be at the definition of hugetlb_vm_ops.