ksm: use a folio in try_to_merge_one_page()

ksm: use a folio in try_to_merge_one_page()

Patch series "Remove PageKsm()".

The KSM flag is almost always tested on the folio rather than on the page.
This series removes the final users of PageKsm() and makes the flag only

This patch (of 5):

It is safe to use a folio here because all callers took a refcount on this
page.  The one wrinkle is that we have to recalculate the value of folio
after splitting the page, since it has probably changed.  Replaces nine
calls to compound_head() with one.

Link: https://lkml.kernel.org/r/20241002152533.1350629-1-willy@infradead.org
Link: https://lkml.kernel.org/r/20241002152533.1350629-2-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Alex Shi <alexs@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>