So if some memory needs to be swapped out to disk (in order to free memory that can be returned to the process calling kmalloc), I understand Disk IO should suffice. But my doubt is how can a filesystem IO help to free memory (so that it can be returned to the process calling kmalloc)?
Ummm ... not sure ... but just a direction to think upon. There memory occupied by VFS / filesystems may be holding some buffers (of certain files). So a file system request may be used to flush these buffers to the disk, and thus free memory to be returned.
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