mm, hugetlb: unify core page allocation accounting and initialization

mm, hugetlb: unify core page allocation accounting and initialization

Patch series "mm, hugetlb: allocation API and migration improvements"

Motivation:

this is a follow up for [3] for the allocation API and [4] for the
hugetlb migration.  It wasn't really easy to split those into two
separate patch series as they share some code.

My primary motivation to touch this code is to make the gigantic pages
migration working.  The giga pages allocation code is just too fragile
and hacked into the hugetlb code now.  This series tries to move giga
pages closer to the first class citizen.  We are not there yet but
having 5 patches is quite a lot already and it will already make the
code much easier to follow.  I will come with other changes on top after
this sees some review.

The first two patches should be trivial to review.  The third patch
changes the way how we migrate huge pages.  Newly allocated pages are a
subject of the overcommit check and they participate surplus accounting
which is quite unfortunate as the changelog explains.  This patch
doesn't change anything wrt.  giga pages.

Patch #4 removes the surplus accounting hack from
__alloc_surplus_huge_page.  I hope I didn't miss anything there and a
deeper review is really due there.

Patch #5 finally unifies allocation paths and giga pages shouldn't be
any special anymore.  There is also some renaming going on as well.

This patch (of 6):

hugetlb allocator has two entry points to the page allocator
 - alloc_fresh_huge_page_node
 - __hugetlb_alloc_buddy_huge_page

The two differ very subtly in two aspects.  The first one doesn't care
about HTLB_BUDDY_* stats and it doesn't initialize the huge page.
prep_new_huge_page is not used because it not only initializes hugetlb
specific stuff but because it also put_page and releases the page to the
hugetlb pool which is not what is required in some contexts.  This makes
things more complicated than necessary.

Simplify things by a) removing the page allocator entry point duplicity
and only keep __hugetlb_alloc_buddy_huge_page and b) make
prep_new_huge_page more reusable by removing the put_page which moves
the page to the allocator pool.  All current callers are updated to call
put_page explicitly.  Later patches will add new callers which won't
need it.

This patch shouldn't introduce any functional change.

Link: http://lkml.kernel.org/r/20180103093213.26329-2-mhocko@kernel.org
Signed-off-by: Michal Hocko <mhocko@suse.com>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Reviewed-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Andrea Reale <ar@linux.vnet.ibm.com>
Cc: Anshuman Khandual <khandual@linux.vnet.ibm.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Zi Yan <zi.yan@cs.rutgers.edu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>