Re: [PATCH] mm: khugepaged: free xarray nodes left behind by failed collapse_file()

[Rik van Riel]

On Tue, Jun 16, 2026 at 10:18 PM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote:
>
> On Wed, Jun 17, 2026 at 10:00:59AM +0800, Jinjiang Tu wrote:

> > I can reproduce it easily with following steps. [1]
> > 1) create file /tmp/test_madvise_collapse and ftruncate to 4MB size, and
> > then mmap the file
> > 2) memset for the first 2MB
> > 3) madvise(MADV_COLLAPSE) for the second 2MB
> > 4) unlink the file
>
> Yes, but is there a problem?  That is, do we need to clear this up
> before we get to clear_inode()?

If there is no harm in leaving this xarray node hang around until
clear_inode() time, I agree we do not need this patch.

Are there no issues with large folios getting inserted into the
xarray at a later time, after zapping little ones, and leaving
the empty xarray node dangling?

If none of this causes issues, we can keep things simple.