On 11.08.22 12:21, Greg KH wrote:
On Thu, Aug 11, 2022 at 11:46:09AM +0200, Alexander Grund wrote:
I mean this patch removes a superflous pointer of the superblock struct making the kernel use less memory.
Also, how much measurable memory does this save? You did not quantify it.
It saves one pointer, i.e. usually 8 Byte, per superblock when using SELinux.
I don't know how many of those superblocks will be allocated in total on usual systems as I'm not familiar with the details of the filesystems. However following one callchain leads to
/*
- Common helper for pseudo-filesystems (sockfs, pipefs, bdev - stuff that
- will never be mountable)
*/ struct dentry *mount_pseudo_xattr(struct file_system_type *fs_type, char *name,
So it seems one superblock even for each pseudo-fs of which there can be many.
A quick experiment [1] on my phone shows about 300 superblocks allocated which means that the patch saves a bit over 2kB of memory. So not that much on usual systems but could be much for some embedded systems.
I hope that helps, Alex
[1] For the experiment I added a debug counter to `superblock_alloc_security`