mm: sparsemem: split the huge PMD mapping of vmemmap pages

Patch series "Split huge PMD mapping of vmemmap pages", v4.

In order to reduce the difficulty of code review in series[1].  We disable
huge PMD mapping of vmemmap pages when that feature is enabled.  In this
series, we do not disable huge PMD mapping of vmemmap pages anymore.  We
will split huge PMD mapping when needed.  When HugeTLB pages are freed
from the pool we do not attempt coalasce and move back to a PMD mapping
because it is much more complex.

[1] https://lore.kernel.org/linux-doc/[email protected]/

This patch (of 3):

In [1], PMD mappings of vmemmap pages were disabled if the the feature
hugetlb_free_vmemmap was enabled.  This was done to simplify the initial
implementation of vmmemap freeing for hugetlb pages.  Now, remove this
simplification by allowing PMD mapping and switching to PTE mappings as
needed for allocated hugetlb pages.

When a hugetlb page is allocated, the vmemmap page tables are walked to
free vmemmap pages.  During this walk, split huge PMD mappings to PTE
mappings as required.  In the unlikely case PTE pages can not be
allocated, return error(ENOMEM) and do not optimize vmemmap of the hugetlb
page.

When HugeTLB pages are freed from the pool, we do not attempt to
coalesce and move back to a PMD mapping because it is much more complex.

[1] https://lkml.kernel.org/r/[email protected]

Link: https://lkml.kernel.org/r/[email protected]
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Muchun Song <[email protected]>
Reviewed-by: Mike Kravetz <[email protected]>
Cc: Oscar Salvador <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: Chen Huang <[email protected]>
Cc: Jonathan Corbet <[email protected]>
Cc: Xiongchun Duan <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

0 files changed, 0 insertions, 0 deletions