Re: [PATCH] fs/kernfs: raise sb->maxbytes to MAX_LFS_FILESIZE

[Greg KH]

On Mon, Nov 24, 2025 at 09:06:21AM -0800, jane.chu@xxxxxxxxxx wrote:
> Hi, Greg,
> 
> On 11/24/2025 8:17 AM, Greg KH wrote:
> > 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?
> 
> This file:  /sys/kernel/mm/page_idle/bitmap
> that tracks idle pages, 1 bit per page.

Why is that a sysfs file and not a debugfs file?

> Because of the above memory span, so even though the system has < 64TiB
> memory, we still need to be able to seek beyond the 2GiB point in the
> /sys/kernel/mm/page_idle/bitmap file.

What uses this file?  It's not on my systems, what arch uses it?

thanks,

greg k-h