linux-kernel - Re: [PATCH] fs/kernfs: raise sb->maxbytes to MAX_LFS

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Message-ID: <2025112410-carnivore-anemia-e6eb@gregkh>
Date: Mon, 24 Nov 2025 17:17:02 +0100
From: Greg KH <gregkh@...uxfoundation.org>
To: Jane Chu <jane.chu@...cle.com>
Cc: tj@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fs/kernfs: raise sb->maxbytes to MAX_LFS_FILESIZE

On Tue, Nov 11, 2025 at 01:26:06PM -0700, Jane Chu wrote:
> On an ARM64 A1 system, it's possible to have physical memory span
> up to the 64T boundary, like below
> 
> $ lsmem -b -r -n -o range,size
> 0x0000000080000000-0x00000000bfffffff 1073741824
> 0x0000080000000000-0x000008007fffffff 2147483648
> 0x00000800c0000000-0x0000087fffffffff 546534588416
> 0x0000400000000000-0x00004000bfffffff 3221225472
> 0x0000400100000000-0x0000407fffffffff 545460846592
> 
> So it's time to extend /sys/kernel/mm/page_idle/bitmap to be able
> to account for >2G number of pages, by raising the kernfs file size
> limit.

Wait, we are having sysfs files that are bigger than >2G?  Which files
exactly?

> Signed-off-by: Jane Chu <jane.chu@...cle.com>
> ---
>  fs/kernfs/mount.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/fs/kernfs/mount.c b/fs/kernfs/mount.c
> index 76eaf64b9d9e..3ac52e141766 100644
> --- a/fs/kernfs/mount.c
> +++ b/fs/kernfs/mount.c
> @@ -298,6 +298,7 @@ static int kernfs_fill_super(struct super_block *sb, struct kernfs_fs_context *k
>  	if (info->root->flags & KERNFS_ROOT_SUPPORT_EXPORTOP)
>  		sb->s_export_op = &kernfs_export_ops;
>  	sb->s_time_gran = 1;
> +	sb->s_maxbytes  = MAX_LFS_FILESIZE;

What is the default setting for s_maxbytes today?

thanks,

greg k-h