linux-kernel - Re: [PATCH] Correct alignment of huge page requests.

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Date:	Sat,  3 Mar 2012 22:02:56 -0500
From:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
To:	Steven Truelove <steven.truelove@...ronto.ca>
Cc:	wli@...omorphy.com, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] Correct alignment of huge page requests.

On Thu, Mar 01, 2012 at 09:58:41PM -0500, Steven Truelove wrote:
> When calling shmget() with SHM_HUGETLB, shmget aligns the request size to PAGE_SIZE, but this is not sufficient.  Modified hugetlb_file_setup() to align requests to the huge page size, and to accept an address argument so that all alignment checks can be performed in hugetlb_file_setup(), rather than in its callers.  Changed newseg and mmap_pgoff to match new prototype and eliminated a now redundant alignment check.

I think only rounding up request size in shmget() is not sufficient,
because later shmat() also have alignment check and fails to mmap()
to unaligned address.
Maybe file->f_op->get_unmapped_area() (or hugetlb_get_unmapped_area())
should have round up code, I think.
Could you try it?

And a few comments below,

> Signed-off-by: Steven Truelove <steven.truelove@...ronto.ca>
> ---
>  fs/hugetlbfs/inode.c    |   12 ++++++++----
>  include/linux/hugetlb.h |    3 ++-
>  ipc/shm.c               |    2 +-
>  mm/mmap.c               |    6 +++---
>  4 files changed, 14 insertions(+), 9 deletions(-)
> 
> diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
> index 1e85a7a..a97b7cc 100644
> --- a/fs/hugetlbfs/inode.c
> +++ b/fs/hugetlbfs/inode.c
> @@ -928,7 +928,7 @@ static int can_do_hugetlb_shm(void)
>  	return capable(CAP_IPC_LOCK) || in_group_p(sysctl_hugetlb_shm_group);
>  }
>  
> -struct file *hugetlb_file_setup(const char *name, size_t size,
> +struct file *hugetlb_file_setup(const char *name, unsigned long addr, size_t size,

Just a nitpick, this line is over 80 characters.
checkpatch.pl should warn.

>  				vm_flags_t acctflag,
>  				struct user_struct **user, int creat_flags)
>  {
> @@ -938,6 +938,8 @@ struct file *hugetlb_file_setup(const char *name, size_t size,
>  	struct path path;
>  	struct dentry *root;
>  	struct qstr quick_string;
> +	struct hstate *hstate;
> +	int num_pages;

Is unsigned long better?

Thanks,
Naoya
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