It's guaranteed that huge_zero_page will not be NULL if
huge_zero_refcount is increased successfully.

When READ_ONCE(huge_zero_page) is returned, there must be a
huge_zero_page and it can be replaced with returning
'true' when we do not care about the value of huge_zero_page.

We can thus make it return bool to save READ_ONCE cpu cycles as the
return value is just used to check if huge_zero_page exists.

Link: https://lkml.kernel.org/r/20210318122722.13135-3-linmiaohe@huawei.comSigned-off-by: NMiaohe Lin <linmiaohe@huawei.com>
Reviewed-by: NZi Yan <ziy@nvidia.com>
Reviewed-by: NPeter Xu <peterx@redhat.com>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Michel Lespinasse <walken@google.com>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Cc: Thomas Hellstrm (Intel) <thomas_os@shipmail.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Wei Yang <richard.weiyang@linux.alibaba.com>
Cc: William Kucharski <william.kucharski@oracle.com>
Cc: Yang Shi <yang.shi@linux.alibaba.com>
Cc: yuleixzhang <yulei.kernel@gmail.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Patch series "Some cleanups for huge_memory", v3.

This series contains cleanups to rework some function logics to make it
more readable, use helper function and so on.  More details can be found
in the respective changelogs.

This patch (of 6):

The current implementation of vma_adjust_trans_huge() contains some
duplicated codes.  Add helper function to get rid of these codes to make
it more succinct.

Link: https://lkml.kernel.org/r/20210318122722.13135-1-linmiaohe@huawei.com
Link: https://lkml.kernel.org/r/20210318122722.13135-2-linmiaohe@huawei.comSigned-off-by: NMiaohe Lin <linmiaohe@huawei.com>
Reviewed-by: NPeter Xu <peterx@redhat.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: William Kucharski <william.kucharski@oracle.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Peter Xu <peterx@redhat.com>
Cc: yuleixzhang <yulei.kernel@gmail.com>
Cc: Michel Lespinasse <walken@google.com>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Cc: Thomas Hellstrm (Intel) <thomas_os@shipmail.org>
Cc: Yang Shi <yang.shi@linux.alibaba.com>
Cc: Wei Yang <richard.weiyang@linux.alibaba.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

There is no need to use a new local variable ret2 to get the return
value of handle_userfault().  Use ret directly to make code more
succinct.

Link: https://lkml.kernel.org/r/20210210072409.60587-1-linmiaohe@huawei.comSigned-off-by: NMiaohe Lin <linmiaohe@huawei.com>
Reviewed-by: NAndrew Morton <akpm@linux-foundation.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

In writable and !referenced case, the result value should be
SCAN_LACK_REFERENCED_PAGE for trace_mm_collapse_huge_page_isolate()
instead of default 0 (SCAN_FAIL) here.

Link: https://lkml.kernel.org/r/20210306032947.35921-5-linmiaohe@huawei.com
Fixes: 7d2eba05 ("mm: add tracepoint for scanning pages")
Signed-off-by: NMiaohe Lin <linmiaohe@huawei.com>
Acked-by: NKirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Ebru Akagunduz <ebru.akagunduz@gmail.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Commit 4d45e75a ("mm: remove the now-unnecessary mmget_still_valid()
hack") have made khugepaged_test_exit() suitable for check mm->mm_users
against 0.  Use this helper here.

Link: https://lkml.kernel.org/r/20210306032947.35921-4-linmiaohe@huawei.comSigned-off-by: NMiaohe Lin <linmiaohe@huawei.com>
Acked-by: NKirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Ebru Akagunduz <ebru.akagunduz@gmail.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

smp_wmb() is needed to avoid the copy_huge_page writes to become visible
after the set_pmd_at() write here.  But we can reuse the smp_wmb() inside
__SetPageUptodate() to remove this redundant one.

Link: https://lkml.kernel.org/r/20210306032947.35921-3-linmiaohe@huawei.comSigned-off-by: NMiaohe Lin <linmiaohe@huawei.com>
Acked-by: NKirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Ebru Akagunduz <ebru.akagunduz@gmail.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Patch series "Cleanup and fixup for khugepaged", v2.

This series contains cleanups to remove unneeded return value, use
helper function and so on.  And there is one fix to correct the wrong
result value for trace_mm_collapse_huge_page_isolate().

This patch (of 4):

The return value of khugepaged_collapse_pte_mapped_thps() is never checked
since it's introduced.  We should remove such unneeded return value.

Link: https://lkml.kernel.org/r/20210306032947.35921-1-linmiaohe@huawei.com
Link: https://lkml.kernel.org/r/20210306032947.35921-2-linmiaohe@huawei.comSigned-off-by: NMiaohe Lin <linmiaohe@huawei.com>
Acked-by: NKirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Ebru Akagunduz <ebru.akagunduz@gmail.com>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

The fault_mutex hashing overhead can be avoided in truncate_op case
because page faults can not race with truncation in this routine.

So calculate hash for fault_mutex only in !truncate_op case to save some
cpu cycles.

Link: https://lkml.kernel.org/r/20210308112809.26107-6-linmiaohe@huawei.comSigned-off-by: NMiaohe Lin <linmiaohe@huawei.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Rework the error handling code when alloc_huge_page() failed to remove
some duplicated code and simplify the code slightly.

Link: https://lkml.kernel.org/r/20210308112809.26107-5-linmiaohe@huawei.comSigned-off-by: NMiaohe Lin <linmiaohe@huawei.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

!PageHuge(oldhpage) is implicitly checked in page_hstate() above, so we
remove this explicit one.

Link: https://lkml.kernel.org/r/20210308112809.26107-4-linmiaohe@huawei.comSigned-off-by: NMiaohe Lin <linmiaohe@huawei.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

We should not transfer the per-node surplus state when we do not cross the
node in order to save some cpu cycles

Link: https://lkml.kernel.org/r/20210308112809.26107-3-linmiaohe@huawei.comSigned-off-by: NMiaohe Lin <linmiaohe@huawei.com>
Reviewed-by: NMike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Patch series "Some cleanups for hugetlb".

This series contains cleanups to remove unnecessary VM_BUG_ON_PAGE, use
helper function and so on.  I also collect some previous patches into this
series in case they are forgotten.

This patch (of 5):

We could use pages_per_huge_page to get the number of pages per hugepage,
use get_hstate_idx to calculate hstate index, and use hstate_is_gigantic
to check if a hstate is gigantic to make code more succinct.

Link: https://lkml.kernel.org/r/20210308112809.26107-1-linmiaohe@huawei.com
Link: https://lkml.kernel.org/r/20210308112809.26107-2-linmiaohe@huawei.comSigned-off-by: NMiaohe Lin <linmiaohe@huawei.com>
Reviewed-by: NMike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

HUGETLB_PAGE_SIZE_VARIABLE need not be defined for each individual
platform subscribing it.  Instead just make it generic.

Link: https://lkml.kernel.org/r/1614914928-22039-1-git-send-email-anshuman.khandual@arm.comSigned-off-by: NAnshuman Khandual <anshuman.khandual@arm.com>
Suggested-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Acked-by: Michael Ellerman <mpe@ellerman.id.au>	[powerpc]
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

vma_resv_map(vma) checks if a reserve map is associated with the vma.
The routine vma_needs_reservation() will check vma_resv_map(vma) and
return 1 if no reserv map is present.  map_chg is set to the return
value of vma_needs_reservation().  Therefore, !vma_resv_map(vma) is
redundant in the expression:

	map_chg || avoid_reserve || !vma_resv_map(vma);

Remove the redundant check.

[Thanks Mike Kravetz for reshaping this commit message!]

Link: https://lkml.kernel.org/r/20210301104726.45159-1-linmiaohe@huawei.comSigned-off-by: NMiaohe Lin <linmiaohe@huawei.com>
Reviewed-by: NMike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Huge pmd sharing for hugetlbfs is racy with userfaultfd-wp because
userfaultfd-wp is always based on pgtable entries, so they cannot be
shared.

Walk the hugetlb range and unshare all such mappings if there is, right
before UFFDIO_REGISTER will succeed and return to userspace.

This will pair with want_pmd_share() in hugetlb code so that huge pmd
sharing is completely disabled for userfaultfd-wp registered range.

Link: https://lkml.kernel.org/r/20210218231206.15524-1-peterx@redhat.comSigned-off-by: NPeter Xu <peterx@redhat.com>
Reviewed-by: NMike Kravetz <mike.kravetz@oracle.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Kirill A. Shutemov <kirill@shutemov.name>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Adam Ruprecht <ruprecht@google.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Cannon Matthews <cannonmatthews@google.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Chinwen Chang <chinwen.chang@mediatek.com>
Cc: David Rientjes <rientjes@google.com>
Cc: "Dr . David Alan Gilbert" <dgilbert@redhat.com>
Cc: Huang Ying <ying.huang@intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jann Horn <jannh@google.com>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: Lokesh Gidra <lokeshgidra@google.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: "Michal Koutn" <mkoutny@suse.com>
Cc: Michel Lespinasse <walken@google.com>
Cc: Mina Almasry <almasrymina@google.com>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Oliver Upton <oupton@google.com>
Cc: Shaohua Li <shli@fb.com>
Cc: Shawn Anastasio <shawn@anastas.io>
Cc: Steven Price <steven.price@arm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Prepare for it to be called outside of mm/hugetlb.c.

Link: https://lkml.kernel.org/r/20210218231204.15474-1-peterx@redhat.comSigned-off-by: NPeter Xu <peterx@redhat.com>
Reviewed-by: NMike Kravetz <mike.kravetz@oracle.com>
Reviewed-by: NAxel Rasmussen <axelrasmussen@google.com>
Cc: Adam Ruprecht <ruprecht@google.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Cannon Matthews <cannonmatthews@google.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Chinwen Chang <chinwen.chang@mediatek.com>
Cc: David Rientjes <rientjes@google.com>
Cc: "Dr . David Alan Gilbert" <dgilbert@redhat.com>
Cc: Huang Ying <ying.huang@intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jann Horn <jannh@google.com>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: Kirill A. Shutemov <kirill@shutemov.name>
Cc: Lokesh Gidra <lokeshgidra@google.com>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: "Michal Koutn" <mkoutny@suse.com>
Cc: Michel Lespinasse <walken@google.com>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Mina Almasry <almasrymina@google.com>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Oliver Upton <oupton@google.com>
Cc: Shaohua Li <shli@fb.com>
Cc: Shawn Anastasio <shawn@anastas.io>
Cc: Steven Price <steven.price@arm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Huge pmd sharing could bring problem to userfaultfd.  The thing is that
userfaultfd is running its logic based on the special bits on page table
entries, however the huge pmd sharing could potentially share page table
entries for different address ranges.  That could cause issues on
either:

 - When sharing huge pmd page tables for an uffd write protected range,
   the newly mapped huge pmd range will also be write protected
   unexpectedly, or,

 - When we try to write protect a range of huge pmd shared range, we'll
   first do huge_pmd_unshare() in hugetlb_change_protection(), however
   that also means the UFFDIO_WRITEPROTECT could be silently skipped for
   the shared region, which could lead to data loss.

While at it, a few other things are done altogether:

 - Move want_pmd_share() from mm/hugetlb.c into linux/hugetlb.h, because
   that's definitely something that arch code would like to use too

 - ARM64 currently directly check against
   CONFIG_ARCH_WANT_HUGE_PMD_SHARE when trying to share huge pmd. Switch
   to the want_pmd_share() helper.

 - Move vma_shareable() from huge_pmd_share() into want_pmd_share().

[peterx@redhat.com: fix build with !ARCH_WANT_HUGE_PMD_SHARE]
  Link: https://lkml.kernel.org/r/20210310185359.88297-1-peterx@redhat.com

Link: https://lkml.kernel.org/r/20210218231202.15426-1-peterx@redhat.comSigned-off-by: NPeter Xu <peterx@redhat.com>
Reviewed-by: NMike Kravetz <mike.kravetz@oracle.com>
Reviewed-by: NAxel Rasmussen <axelrasmussen@google.com>
Tested-by: NNaresh Kamboju <naresh.kamboju@linaro.org>
Cc: Adam Ruprecht <ruprecht@google.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Cannon Matthews <cannonmatthews@google.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Chinwen Chang <chinwen.chang@mediatek.com>
Cc: David Rientjes <rientjes@google.com>
Cc: "Dr . David Alan Gilbert" <dgilbert@redhat.com>
Cc: Huang Ying <ying.huang@intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jann Horn <jannh@google.com>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: Kirill A. Shutemov <kirill@shutemov.name>
Cc: Lokesh Gidra <lokeshgidra@google.com>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: "Michal Koutn" <mkoutny@suse.com>
Cc: Michel Lespinasse <walken@google.com>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Mina Almasry <almasrymina@google.com>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Oliver Upton <oupton@google.com>
Cc: Shaohua Li <shli@fb.com>
Cc: Shawn Anastasio <shawn@anastas.io>
Cc: Steven Price <steven.price@arm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Patch series "hugetlb: Disable huge pmd unshare for uffd-wp", v4.

This series tries to disable huge pmd unshare of hugetlbfs backed memory
for uffd-wp.  Although uffd-wp of hugetlbfs is still during rfc stage,
the idea of this series may be needed for multiple tasks (Axel's uffd
minor fault series, and Mike's soft dirty series), so I picked it out
from the larger series.

This patch (of 4):

It is a preparation work to be able to behave differently in the per
architecture huge_pte_alloc() according to different VMA attributes.

Pass it deeper into huge_pmd_share() so that we can avoid the find_vma() call.

[peterx@redhat.com: build fix]
  Link: https://lkml.kernel.org/r/20210304164653.GB397383@xz-x1Link: https://lkml.kernel.org/r/20210218230633.15028-1-peterx@redhat.com

Link: https://lkml.kernel.org/r/20210218230633.15028-2-peterx@redhat.comSigned-off-by: NPeter Xu <peterx@redhat.com>
Suggested-by: NMike Kravetz <mike.kravetz@oracle.com>
Cc: Adam Ruprecht <ruprecht@google.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Cannon Matthews <cannonmatthews@google.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Chinwen Chang <chinwen.chang@mediatek.com>
Cc: David Rientjes <rientjes@google.com>
Cc: "Dr . David Alan Gilbert" <dgilbert@redhat.com>
Cc: Huang Ying <ying.huang@intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jann Horn <jannh@google.com>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: Kirill A. Shutemov <kirill@shutemov.name>
Cc: Lokesh Gidra <lokeshgidra@google.com>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: "Michal Koutn" <mkoutny@suse.com>
Cc: Michel Lespinasse <walken@google.com>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Mina Almasry <almasrymina@google.com>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Oliver Upton <oupton@google.com>
Cc: Shaohua Li <shli@fb.com>
Cc: Shawn Anastasio <shawn@anastas.io>
Cc: Steven Price <steven.price@arm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

clear_inode()'s BUG_ON(!mapping_empty(&inode->i_data)) is unsafe: we
know of two ways in which nodes can and do (on rare occasions) get left
behind.  Until those are fixed, do not BUG_ON() nor even WARN_ON().

Yes, this will then leak those nodes (or the next user of the struct
inode may use them); but this has been happening for years, and the new
BUG_ON(!mapping_empty) was only guilty of revealing that.  A proper fix
will follow, but no hurry.

Link: https://lkml.kernel.org/r/alpine.LSU.2.11.2104292229380.16080@eggly.anvilsSigned-off-by: NHugh Dickins <hughd@google.com>
Cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

We no longer track anything in nrexceptional, so remove it, saving 8 bytes
per inode.

Link: https://lkml.kernel.org/r/20201026151849.24232-5-willy@infradead.orgSigned-off-by: NMatthew Wilcox (Oracle) <willy@infradead.org>
Tested-by: NVishal Verma <vishal.l.verma@intel.com>
Acked-by: NJohannes Weiner <hannes@cmpxchg.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Simplify mapping_needs_writeback() by accounting DAX entries as pages
instead of exceptional entries.

Link: https://lkml.kernel.org/r/20201026151849.24232-4-willy@infradead.orgSigned-off-by: NMatthew Wilcox (Oracle) <willy@infradead.org>
Tested-by: NVishal Verma <vishal.l.verma@intel.com>
Acked-by: NJohannes Weiner <hannes@cmpxchg.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

We no longer need to keep track of how many shadow entries are present in
a mapping.  This saves a few writes to the inode and memory barriers.

Link: https://lkml.kernel.org/r/20201026151849.24232-3-willy@infradead.orgSigned-off-by: NMatthew Wilcox (Oracle) <willy@infradead.org>
Tested-by: NVishal Verma <vishal.l.verma@intel.com>
Acked-by: NJohannes Weiner <hannes@cmpxchg.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Patch series "Remove nrexceptional tracking", v2.

We actually use nrexceptional for very little these days.  It's a minor
pain to keep in sync with nrpages, but the pain becomes much bigger with
the THP patches because we don't know how many indices a shadow entry
occupies.  It's easier to just remove it than keep it accurate.

Also, we save 8 bytes per inode which is nothing to sneeze at; on my
laptop, it would improve shmem_inode_cache from 22 to 23 objects per
16kB, and inode_cache from 26 to 27 objects.  Combined, that saves
a megabyte of memory from a combined usage of 25MB for both caches.
Unfortunately, ext4 doesn't cross a magic boundary, so it doesn't save
any memory for ext4.

This patch (of 4):

Instead of checking the two counters (nrpages and nrexceptional), we can
just check whether i_pages is empty.

Link: https://lkml.kernel.org/r/20201026151849.24232-1-willy@infradead.org
Link: https://lkml.kernel.org/r/20201026151849.24232-2-willy@infradead.orgSigned-off-by: NMatthew Wilcox (Oracle) <willy@infradead.org>
Tested-by: NVishal Verma <vishal.l.verma@intel.com>
Acked-by: NJohannes Weiner <hannes@cmpxchg.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

It appears that unmap_mapping_range() actually takes a 'size' as its third
argument rather than a location, the current calling fashion causes
unnecessary amount of unmapping to occur.

Link: https://lkml.kernel.org/r/20210420002821.2749748-1-jane.chu@oracle.com
Fixes: 6100e34b ("mm, memory_failure: Teach memory_failure() about dev_pagemap pages")
Signed-off-by: NJane Chu <jane.chu@oracle.com>
Reviewed-by: NDan Williams <dan.j.williams@intel.com>
Reviewed-by: NNaoya Horiguchi <naoya.horiguchi@nec.com>
Cc: Dave Jiang <dave.jiang@intel.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

There are a couple of kernel-doc comments in include/linux/mmzone.h but
they have minor formatting issues that would cause kernel-doc warnings.

Fix the formatting of those comments, add missing Return: descriptions and
link include/linux/mmzone.h to Documentation/core-api/mm-api.rst

Link: https://lkml.kernel.org/r/20210426141927.1314326-2-rppt@kernel.orgSigned-off-by: NMike Rapoport <rppt@linux.ibm.com>
Reviewed-by: NMatthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: NAnshuman Khandual <anshuman.khandual@arm.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

On !ARCH_SUPPORTS_DEBUG_PAGEALLOC (like ia64) debug_pagealloc=1 implies
page_poison=on:

    if (page_poisoning_enabled() ||
         (!IS_ENABLED(CONFIG_ARCH_SUPPORTS_DEBUG_PAGEALLOC) &&
          debug_pagealloc_enabled()))
            static_branch_enable(&_page_poisoning_enabled);

page_poison=on needs to override init_on_free=1.

Before the change it did not work as expected for the following case:
- have PAGE_POISONING=y
- have page_poison unset
- have !ARCH_SUPPORTS_DEBUG_PAGEALLOC arch (like ia64)
- have init_on_free=1
- have debug_pagealloc=1

That way we get both keys enabled:
- static_branch_enable(&init_on_free);
- static_branch_enable(&_page_poisoning_enabled);

which leads to poisoned pages returned for __GFP_ZERO pages.

After the change we execute only:
- static_branch_enable(&_page_poisoning_enabled);
  and ignore init_on_free=1.

Link: https://lkml.kernel.org/r/20210329222555.3077928-1-slyfox@gentoo.org
Link: https://lkml.org/lkml/2021/3/26/443
Fixes: 8db26a3d ("mm, page_poison: use static key more efficiently")
Signed-off-by: NSergei Trofimovich <slyfox@gentoo.org>
Acked-by: NVlastimil Babka <vbabka@suse.cz>
Reviewed-by: NDavid Hildenbrand <david@redhat.com>
Cc: Andrey Konovalov <andreyknvl@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

There are cases where the page_pool need to refill with pages from the
page allocator.  Some workloads cause the page_pool to release pages
instead of recycling these pages.

For these workload it can improve performance to bulk alloc pages from the
page-allocator to refill the alloc cache.

For XDP-redirect workload with 100G mlx5 driver (that use page_pool)
redirecting xdp_frame packets into a veth, that does XDP_PASS to create an
SKB from the xdp_frame, which then cannot return the page to the
page_pool.

Performance results under GitHub xdp-project[1]:
 [1] https://github.com/xdp-project/xdp-project/blob/master/areas/mem/page_pool06_alloc_pages_bulk.org

Mel: The patch "net: page_pool: convert to use alloc_pages_bulk_array
variant" was squashed with this patch. From the test page, the array
variant was superior with one of the test results as follows.

	Kernel		XDP stats       CPU     pps           Delta
	Baseline	XDP-RX CPU      total   3,771,046       n/a
	List		XDP-RX CPU      total   3,940,242    +4.49%
	Array		XDP-RX CPU      total   4,249,224   +12.68%

Link: https://lkml.kernel.org/r/20210325114228.27719-10-mgorman@techsingularity.netSigned-off-by: NJesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: NMel Gorman <mgorman@techsingularity.net>
Reviewed-by: NAlexander Lobakin <alobakin@pm.me>
Cc: Alexander Duyck <alexander.duyck@gmail.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Chuck Lever <chuck.lever@oracle.com>
Cc: David Miller <davem@davemloft.net>
Cc: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

In preparation for next patch, move the dma mapping into its own function,
as this will make it easier to follow the changes.

[ilias.apalodimas: make page_pool_dma_map return boolean]

Link: https://lkml.kernel.org/r/20210325114228.27719-9-mgorman@techsingularity.netSigned-off-by: NJesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: NMel Gorman <mgorman@techsingularity.net>
Reviewed-by: NIlias Apalodimas <ilias.apalodimas@linaro.org>
Reviewed-by: NAlexander Lobakin <alobakin@pm.me>
Cc: Alexander Duyck <alexander.duyck@gmail.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Chuck Lever <chuck.lever@oracle.com>
Cc: David Miller <davem@davemloft.net>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Reduce the rate at which nfsd threads hammer on the page allocator.  This
improves throughput scalability by enabling the threads to run more
independently of each other.

[mgorman: Update interpretation of alloc_pages_bulk return value]

Link: https://lkml.kernel.org/r/20210325114228.27719-8-mgorman@techsingularity.netSigned-off-by: NChuck Lever <chuck.lever@oracle.com>
Signed-off-by: NMel Gorman <mgorman@techsingularity.net>
Reviewed-by: NAlexander Lobakin <alobakin@pm.me>
Cc: Alexander Duyck <alexander.duyck@gmail.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: David Miller <davem@davemloft.net>
Cc: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Cc: Jesper Dangaard Brouer <brouer@redhat.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Patch series "SUNRPC consumer for the bulk page allocator"

This patch set and the measurements below are based on yesterday's
bulk allocator series:

  git://git.kernel.org/pub/scm/linux/kernel/git/mel/linux.git mm-bulk-rebase-v5r9

The patches change SUNRPC to invoke the array-based bulk allocator
instead of alloc_page().

The micro-benchmark results are promising.  I ran a mixture of 256KB
reads and writes over NFSv3.  The server's kernel is built with KASAN
enabled, so the comparison is exaggerated but I believe it is still
valid.

I instrumented svc_recv() to measure the latency of each call to
svc_alloc_arg() and report it via a trace point.  The following results
are averages across the trace events.

  Single page: 25.007 us per call over 532,571 calls
  Bulk list:    6.258 us per call over 517,034 calls
  Bulk array:   4.590 us per call over 517,442 calls

This patch (of 2)

Refactor:

I'm about to use the loop variable @i for something else.

As far as the "i++" is concerned, that is a post-increment. The
value of @i is not used subsequently, so the increment operator
is unnecessary and can be removed.

Also note that nfsd_read_actor() was renamed nfsd_splice_actor()
by commit cf8208d0 ("sendfile: convert nfsd to
splice_direct_to_actor()").

Link: https://lkml.kernel.org/r/20210325114228.27719-7-mgorman@techsingularity.netSigned-off-by: NChuck Lever <chuck.lever@oracle.com>
Signed-off-by: NMel Gorman <mgorman@techsingularity.net>
Reviewed-by: NAlexander Lobakin <alobakin@pm.me>
Cc: Alexander Duyck <alexander.duyck@gmail.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: David Miller <davem@davemloft.net>
Cc: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Cc: Jesper Dangaard Brouer <brouer@redhat.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

When __alloc_pages_bulk() got introduced two callers of __rmqueue_pcplist
exist and the compiler chooses to not inline this function.

  ./scripts/bloat-o-meter vmlinux-before vmlinux-inline__rmqueue_pcplist
  add/remove: 0/1 grow/shrink: 2/0 up/down: 164/-125 (39)
  Function                                     old     new   delta
  rmqueue                                     2197    2296     +99
  __alloc_pages_bulk                          1921    1986     +65
  __rmqueue_pcplist                            125       -    -125
  Total: Before=19374127, After=19374166, chg +0.00%

modprobe page_bench04_bulk loops=$((10**7))

Type:time_bulk_page_alloc_free_array
 -  Per elem: 106 cycles(tsc) 29.595 ns (step:64)
 - (measurement period time:0.295955434 sec time_interval:295955434)
 - (invoke count:10000000 tsc_interval:1065447105)

Before:
 - Per elem: 110 cycles(tsc) 30.633 ns (step:64)

Link: https://lkml.kernel.org/r/20210325114228.27719-6-mgorman@techsingularity.netSigned-off-by: NJesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: NMel Gorman <mgorman@techsingularity.net>
Reviewed-by: NAlexander Lobakin <alobakin@pm.me>
Acked-by: NVlastimil Babka <vbabka@suse.cz>
Cc: Alexander Duyck <alexander.duyck@gmail.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Chuck Lever <chuck.lever@oracle.com>
Cc: David Miller <davem@davemloft.net>
Cc: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Looking at perf-report and ASM-code for __alloc_pages_bulk() it is clear
that the code activated is suboptimal.  The compiler guesses wrong and
places unlikely code at the beginning.  Due to the use of WARN_ON_ONCE()
macro the UD2 asm instruction is added to the code, which confuse the
I-cache prefetcher in the CPU.

[mgorman@techsingularity.net: minor changes and rebasing]

Link: https://lkml.kernel.org/r/20210325114228.27719-5-mgorman@techsingularity.netSigned-off-by: NJesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: NMel Gorman <mgorman@techsingularity.net>
Reviewed-by: NAlexander Lobakin <alobakin@pm.me>
Acked-By: NVlastimil Babka <vbabka@suse.cz>
Cc: Alexander Duyck <alexander.duyck@gmail.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Chuck Lever <chuck.lever@oracle.com>
Cc: David Miller <davem@davemloft.net>
Cc: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

The proposed callers for the bulk allocator store pages from the bulk
allocator in an array.  This patch adds an array-based interface to the
API to avoid multiple list iterations.  The page list interface is
preserved to avoid requiring all users of the bulk API to allocate and
manage enough storage to store the pages.

[akpm@linux-foundation.org: remove now unused local `allocated']

Link: https://lkml.kernel.org/r/20210325114228.27719-4-mgorman@techsingularity.netSigned-off-by: NMel Gorman <mgorman@techsingularity.net>
Reviewed-by: NAlexander Lobakin <alobakin@pm.me>
Acked-by: NVlastimil Babka <vbabka@suse.cz>
Cc: Alexander Duyck <alexander.duyck@gmail.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Chuck Lever <chuck.lever@oracle.com>
Cc: David Miller <davem@davemloft.net>
Cc: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Cc: Jesper Dangaard Brouer <brouer@redhat.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

This patch adds a new page allocator interface via alloc_pages_bulk, and
__alloc_pages_bulk_nodemask.  A caller requests a number of pages to be
allocated and added to a list.

The API is not guaranteed to return the requested number of pages and
may fail if the preferred allocation zone has limited free memory, the
cpuset changes during the allocation or page debugging decides to fail
an allocation.  It's up to the caller to request more pages in batch if
necessary.

Note that this implementation is not very efficient and could be
improved but it would require refactoring.  The intent is to make it
available early to determine what semantics are required by different
callers.  Once the full semantics are nailed down, it can be refactored.

[mgorman@techsingularity.net: fix alloc_pages_bulk() return type, per Matthew]
  Link: https://lkml.kernel.org/r/20210325123713.GQ3697@techsingularity.net
[mgorman@techsingularity.net: fix uninit var warning]
  Link: https://lkml.kernel.org/r/20210330114847.GX3697@techsingularity.net
[mgorman@techsingularity.net: fix comment, per Vlastimil]
  Link: https://lkml.kernel.org/r/20210412110255.GV3697@techsingularity.net

Link: https://lkml.kernel.org/r/20210325114228.27719-3-mgorman@techsingularity.netSigned-off-by: NMel Gorman <mgorman@techsingularity.net>
Acked-by: NVlastimil Babka <vbabka@suse.cz>
Reviewed-by: NAlexander Lobakin <alobakin@pm.me>
Tested-by: NColin Ian King <colin.king@canonical.com>
Cc: Alexander Duyck <alexander.duyck@gmail.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Chuck Lever <chuck.lever@oracle.com>
Cc: David Miller <davem@davemloft.net>
Cc: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Cc: Jesper Dangaard Brouer <brouer@redhat.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Patch series "Introduce a bulk order-0 page allocator with two in-tree users", v6.

This series introduces a bulk order-0 page allocator with sunrpc and the
network page pool being the first users.  The implementation is not
efficient as semantics needed to be ironed out first.  If no other
semantic changes are needed, it can be made more efficient.  Despite that,
this is a performance-related for users that require multiple pages for an
operation without multiple round-trips to the page allocator.  Quoting the
last patch for the high-speed networking use-case

            Kernel          XDP stats       CPU     pps           Delta
            Baseline        XDP-RX CPU      total   3,771,046       n/a
            List            XDP-RX CPU      total   3,940,242    +4.49%
            Array           XDP-RX CPU      total   4,249,224   +12.68%

Via the SUNRPC traces of svc_alloc_arg()

	Single page: 25.007 us per call over 532,571 calls
	Bulk list:    6.258 us per call over 517,034 calls
	Bulk array:   4.590 us per call over 517,442 calls

Both potential users in this series are corner cases (NFS and high-speed
networks) so it is unlikely that most users will see any benefit in the
short term.  Other potential other users are batch allocations for page
cache readahead, fault around and SLUB allocations when high-order pages
are unavailable.  It's unknown how much benefit would be seen by
converting multiple page allocation calls to a single batch or what
difference it may make to headline performance.

Light testing of my own running dbench over NFS passed.  Chuck and Jesper
conducted their own tests and details are included in the changelogs.

Patch 1 renames a variable name that is particularly unpopular

Patch 2 adds a bulk page allocator

Patch 3 adds an array-based version of the bulk allocator

Patches 4-5 adds micro-optimisations to the implementation

Patches 6-7 SUNRPC user

Patches 8-9 Network page_pool user

This patch (of 9):

Review feedback of the bulk allocator twice found problems with "alloced"
being a counter for pages allocated.  The naming was based on the API name
"alloc" and was based on the idea that verbal communication about malloc
tends to use the fake word "malloced" instead of the fake word mallocated.
To be consistent, this preparation patch renames alloced to allocated in
rmqueue_bulk so the bulk allocator and per-cpu allocator use similar names
when the bulk allocator is introduced.

Link: https://lkml.kernel.org/r/20210325114228.27719-1-mgorman@techsingularity.net
Link: https://lkml.kernel.org/r/20210325114228.27719-2-mgorman@techsingularity.netSigned-off-by: NMel Gorman <mgorman@techsingularity.net>
Reviewed-by: NMatthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: NAlexander Lobakin <alobakin@pm.me>
Acked-by: NVlastimil Babka <vbabka@suse.cz>
Cc: Chuck Lever <chuck.lever@oracle.com>
Cc: Jesper Dangaard Brouer <brouer@redhat.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Alexander Duyck <alexander.duyck@gmail.com>
Cc: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Cc: David Miller <davem@davemloft.net>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

linux/vmalloc.h is repeatedly in the file page_alloc.c

Link: https://lkml.kernel.org/r/1616468751-80656-1-git-send-email-zhouchuangao@vivo.comSigned-off-by: Nzhouchuangao <zhouchuangao@vivo.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

The start_pfn and end_pfn are already available in move_freepages_block(),
there is no need to go back and forth between page and pfn in
move_freepages and move_freepages_block, and pfn_valid_within() should
validate pfn first before touching the page.

Link: https://lkml.kernel.org/r/20210323131215.934472-1-liushixin2@huawei.comSigned-off-by: NKefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: NLiu Shixin <liushixin2@huawei.com>
Reviewed-by: NMatthew Wilcox (Oracle) <willy@infradead.org>
Acked-by: NVlastimil Babka <vbabka@suse.cz>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Michal Hocko <mhocko@suse.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Commit 214496cb ("ia64: make SPARSEMEM default and disable
DISCONTIGMEM") removed the last enabler of ARCH_DISCONTIGMEM_DEFAULT,
hence the memory model can no longer default to DISCONTIGMEM_MANUAL.

Link: https://lkml.kernel.org/r/20210312141208.3465520-1-geert@linux-m68k.orgSigned-off-by: NGeert Uytterhoeven <geert@linux-m68k.org>
Reviewed-by: NMike Rapoport <rppt@linux.ibm.com>
Reviewed-by: NDavid Hildenbrand <david@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Currently, debugging CMA allocation failures is quite limited.  The most
common source of these failures seems to be page migration which doesn't
provide any useful information on the reason of the failure by itself.
alloc_contig_range can report those failures as it holds a list of
migrate-failed pages.

The information logged by dump_page() has already proven helpful for
debugging allocation issues, like identifying long-term pinnings on
ZONE_MOVABLE or MIGRATE_CMA.

Let's use the dynamic debugging infrastructure, such that we avoid
flooding the logs and creating a lot of noise on frequent
alloc_contig_range() calls.  This information is helpful for debugging
only.

There are two ifdefery conditions to support common dyndbg options:

 - CONFIG_DYNAMIC_DEBUG_CORE && DYNAMIC_DEBUG_MODULE
   It aims for supporting the feature with only specific file with
   adding ccflags.

 - CONFIG_DYNAMIC_DEBUG
   It aims for supporting the feature with system wide globally.

A simple example to enable the feature:

Admin could enable the dump like this(by default, disabled)

	echo "func alloc_contig_dump_pages +p" > control

Admin could disable it.

	echo "func alloc_contig_dump_pages =_" > control

Detail goes Documentation/admin-guide/dynamic-debug-howto.rst

A concern is utility functions in dump_page use inconsistent
loglevels. In the future, we might want to make the loglevels
used inside dump_page() consistent and eventually rework the way
we log the information here. See [1].

[1] https://lore.kernel.org/linux-mm/YEh4doXvyuRl5BDB@google.com/

Link: https://lkml.kernel.org/r/20210311194042.825152-1-minchan@kernel.orgSigned-off-by: NMinchan Kim <minchan@kernel.org>
Reviewed-by: NDavid Hildenbrand <david@redhat.com>
Cc: John Dias <joaodias@google.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Jason Baron <jbaron@akamai.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Sphinx interprets the Return section as a list and complains about it.
Turn it into a sentence and move it to the end of the kernel-doc to fit
the kernel-doc style.

Link: https://lkml.kernel.org/r/20210225150642.2582252-8-willy@infradead.orgSigned-off-by: NMatthew Wilcox (Oracle) <willy@infradead.org>
Acked-by: NMike Rapoport <rppt@linux.ibm.com>
Acked-by: NVlastimil Babka <vbabka@suse.cz>
Cc: Michal Hocko <mhocko@suse.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>