linux-toradex.git/include/linux/huge_mm.h, branch v6.7-rc2

mm: convert prep_transhuge_page() to folio_prep_large_rmappable()

2023-08-21T21:28:43+00:00

Match folio_undo_large_rmappable(), and move the casting from page to
folio into the callers (which they were largely doing anyway).

Link: https://lkml.kernel.org/r/20230816151201.3655946-6-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) 
Cc: David Hildenbrand 
Cc: Jens Axboe 
Cc: Sidhartha Kumar 
Cc: Yanteng Si 
Signed-off-by: Andrew Morton

mm: convert free_transhuge_folio() to folio_undo_large_rmappable()

2023-08-21T21:28:43+00:00

Indirect calls are expensive, thanks to Spectre.  Test for
TRANSHUGE_PAGE_DTOR and destroy the folio appropriately.  Move the
free_compound_page() call into destroy_large_folio() to simplify later
patches.

Link: https://lkml.kernel.org/r/20230816151201.3655946-5-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) 
Cc: David Hildenbrand 
Cc: Jens Axboe 
Cc: Sidhartha Kumar 
Cc: Yanteng Si 
Signed-off-by: Andrew Morton

smaps: use vm_normal_page_pmd() instead of follow_trans_huge_pmd()

2023-08-21T20:07:20+00:00

We shouldn't be using a GUP-internal helper if it can be avoided.

Similar to smaps_pte_entry() that uses vm_normal_page(), let's use
vm_normal_page_pmd() that similarly refuses to return the huge zeropage.

In contrast to follow_trans_huge_pmd(), vm_normal_page_pmd():

(1) Will always return the head page, not a tail page of a THP.

 If we'd ever call smaps_account with a tail page while setting "compound
 = true", we could be in trouble, because smaps_account() would look at
 the memmap of unrelated pages.

 If we're unlucky, that memmap does not exist at all. Before we removed
 PG_doublemap, we could have triggered something similar as in
 commit 24d7275ce279 ("fs/proc: task_mmu.c: don't read mapcount for
 migration entry").

 This can theoretically happen ever since commit ff9f47f6f00c ("mm: proc:
 smaps_rollup: do not stall write attempts on mmap_lock"):

  (a) We're in show_smaps_rollup() and processed a VMA
  (b) We release the mmap lock in show_smaps_rollup() because it is
      contended
  (c) We merged that VMA with another VMA
  (d) We collapsed a THP in that merged VMA at that position

 If the end address of the original VMA falls into the middle of a THP
 area, we would call smap_gather_stats() with a start address that falls
 into a PMD-mapped THP. It's probably very rare to trigger when not
 really forced.

(2) Will succeed on a is_pci_p2pdma_page(), like vm_normal_page()

 Treat such PMDs here just like smaps_pte_entry() would treat such PTEs.
 If such pages would be anonymous, we most certainly would want to
 account them.

(3) Will skip over pmd_devmap(), like vm_normal_page() for pte_devmap()

 As noted in vm_normal_page(), that is only for handling legacy ZONE_DEVICE
 pages. So just like smaps_pte_entry(), we'll now also ignore such PMD
 entries.

 Especially, follow_pmd_mask() never ends up calling
 follow_trans_huge_pmd() on pmd_devmap(). Instead it calls
 follow_devmap_pmd() -- which will fail if neither FOLL_GET nor FOLL_PIN
 is set.

 So skipping pmd_devmap() pages seems to be the right thing to do.

(4) Will properly handle VM_MIXEDMAP/VM_PFNMAP, like vm_normal_page()

 We won't be returning a memmap that should be ignored by core-mm, or
 worse, a memmap that does not even exist. Note that while
 walk_page_range() will skip VM_PFNMAP mappings, walk_page_vma() won't.

 Most probably this case doesn't currently really happen on the PMD level,
 otherwise we'd already be able to trigger kernel crashes when reading
 smaps / smaps_rollup.

So most probably only (1) is relevant in practice as of now, but could only
cause trouble in extreme corner cases.

Let's move follow_trans_huge_pmd() to mm/internal.h to discourage future
reuse in wrong context.

Link: https://lkml.kernel.org/r/20230803143208.383663-3-david@redhat.com
Fixes: ff9f47f6f00c ("mm: proc: smaps_rollup: do not stall write attempts on mmap_lock")
Signed-off-by: David Hildenbrand 
Acked-by: Mel Gorman 
Cc: Hugh Dickins 
Cc: Jason Gunthorpe 
Cc: John Hubbard 
Cc: Linus Torvalds 
Cc: liubo 
Cc: Matthew Wilcox (Oracle) 
Cc: Mel Gorman 
Cc: Paolo Bonzini 
Cc: Peter Xu 
Cc: Shuah Khan 
Signed-off-by: Andrew Morton

mm: remove vmf_insert_pfn_xxx_prot() for huge page-table entries

2023-04-06T02:42:56+00:00

This functionality's sole user, the drm ttm module, removed support for it
in commit 0d979509539e ("drm/ttm: remove ttm_bo_vm_insert_huge()") as the
whole approach is currently unworkable without a PMD/PUD special bit and
updates to GUP.

Link: https://lkml.kernel.org/r/604c2ad79659d4b8a6e3e1611c6219d5d3233988.1678661628.git.lstoakes@gmail.com
Signed-off-by: Lorenzo Stoakes 
Cc: Christian König 
Cc: Dan Williams 
Cc: Jason Gunthorpe 
Cc: Kirill A. Shutemov 
Cc: Matthew Wilcox (Oracle) 
Cc: Michal Hocko 
Cc: Thomas Hellström 
Cc: Aaron Tomlin 
Cc: Christoph Lameter 
Cc: Frederic Weisbecker 
Cc: Heiko Carstens 
Cc: Huacai Chen 
Cc: Marcelo Tosatti 
Cc: Peter Xu 
Cc: "Russell King (Oracle)" 
Cc: Vlastimil Babka 
Signed-off-by: Andrew Morton

mm/thp: rename TRANSPARENT_HUGEPAGE_NEVER_DAX to _UNSUPPORTED

2023-03-28T23:20:18+00:00

TRANSPARENT_HUGEPAGE_NEVER_DAX has nothing to do with DAX.  It's set when
has_transparent_hugepage() returns false, checked in hugepage_vma_check()
and will disable THP completely if false.  Rename it to
TRANSPARENT_HUGEPAGE_UNSUPPORTED to reflect its real purpose.

[peterx@redhat.com: fix comment, per David]
  Link: https://lkml.kernel.org/r/ZBMzQW674oHQJV7F@x1n
Link: https://lkml.kernel.org/r/20230315171642.1244625-1-peterx@redhat.com
Signed-off-by: Peter Xu 
Acked-by: David Hildenbrand 
Cc: Aneesh Kumar K.V 
Cc: Yang Shi 
Signed-off-by: Andrew Morton

mm: convert deferred_split_huge_page() to deferred_split_folio()

2023-02-03T06:33:00+00:00

Now that both callers use a folio, pass the folio in and save a call to
compound_head().

Link: https://lkml.kernel.org/r/20230111142915.1001531-28-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) 
Signed-off-by: Andrew Morton

mm/huge_memory: remove page_deferred_list()

2023-02-03T06:33:00+00:00

Use folio->_deferred_list directly.

Link: https://lkml.kernel.org/r/20230111142915.1001531-26-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) 
Signed-off-by: Andrew Morton

mm: move page->deferred_list to folio->_deferred_list

2023-02-03T06:33:00+00:00

Remove the entire block of definitions for the second tail page, and add
the deferred list to the struct folio.  This actually moves _deferred_list
to a different offset in struct folio because I don't see a need to
include the padding.

This lets us use list_for_each_entry_safe() in deferred_split_scan()
and avoid a number of calls to compound_head().

Link: https://lkml.kernel.org/r/20230111142915.1001531-25-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) 
Signed-off-by: Andrew Morton

mm: add split_folio()

2022-10-03T21:02:45+00:00

This wrapper removes a need to use split_huge_page(&folio->page).  Convert
two callers.

Link: https://lkml.kernel.org/r/20220902194653.1739778-5-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) 
Signed-off-by: Andrew Morton

mm/madvise: introduce MADV_COLLAPSE sync hugepage collapse

2022-09-12T03:25:46+00:00

This idea was introduced by David Rientjes[1].

Introduce a new madvise mode, MADV_COLLAPSE, that allows users to request
a synchronous collapse of memory at their own expense.

The benefits of this approach are:

* CPU is charged to the process that wants to spend the cycles for the
  THP
* Avoid unpredictable timing of khugepaged collapse

Semantics

This call is independent of the system-wide THP sysfs settings, but will
fail for memory marked VM_NOHUGEPAGE.  If the ranges provided span
multiple VMAs, the semantics of the collapse over each VMA is independent
from the others.  This implies a hugepage cannot cross a VMA boundary.  If
collapse of a given hugepage-aligned/sized region fails, the operation may
continue to attempt collapsing the remainder of memory specified.

The memory ranges provided must be page-aligned, but are not required to
be hugepage-aligned.  If the memory ranges are not hugepage-aligned, the
start/end of the range will be clamped to the first/last hugepage-aligned
address covered by said range.  The memory ranges must span at least one
hugepage-sized region.

All non-resident pages covered by the range will first be
swapped/faulted-in, before being internally copied onto a freshly
allocated hugepage.  Unmapped pages will have their data directly
initialized to 0 in the new hugepage.  However, for every eligible
hugepage aligned/sized region to-be collapsed, at least one page must
currently be backed by memory (a PMD covering the address range must
already exist).

Allocation for the new hugepage may enter direct reclaim and/or
compaction, regardless of VMA flags.  When the system has multiple NUMA
nodes, the hugepage will be allocated from the node providing the most
native pages.  This operation operates on the current state of the
specified process and makes no persistent changes or guarantees on how
pages will be mapped, constructed, or faulted in the future

Return Value

If all hugepage-sized/aligned regions covered by the provided range were
either successfully collapsed, or were already PMD-mapped THPs, this
operation will be deemed successful.  On success, process_madvise(2)
returns the number of bytes advised, and madvise(2) returns 0.  Else, -1
is returned and errno is set to indicate the error for the most-recently
attempted hugepage collapse.  Note that many failures might have occurred,
since the operation may continue to collapse in the event a single
hugepage-sized/aligned region fails.

	ENOMEM	Memory allocation failed or VMA not found
	EBUSY	Memcg charging failed
	EAGAIN	Required resource temporarily unavailable.  Try again
		might succeed.
	EINVAL	Other error: No PMD found, subpage doesn't have Present
		bit set, "Special" page no backed by struct page, VMA
		incorrectly sized, address not page-aligned, ...

Most notable here is ENOMEM and EBUSY (new to madvise) which are intended
to provide the caller with actionable feedback so they may take an
appropriate fallback measure.

Use Cases

An immediate user of this new functionality are malloc() implementations
that manage memory in hugepage-sized chunks, but sometimes subrelease
memory back to the system in native-sized chunks via MADV_DONTNEED;
zapping the pmd.  Later, when the memory is hot, the implementation could
madvise(MADV_COLLAPSE) to re-back the memory by THPs to regain hugepage
coverage and dTLB performance.  TCMalloc is such an implementation that
could benefit from this[2].

Only privately-mapped anon memory is supported for now, but additional
support for file, shmem, and HugeTLB high-granularity mappings[2] is
expected.  File and tmpfs/shmem support would permit:

* Backing executable text by THPs.  Current support provided by
  CONFIG_READ_ONLY_THP_FOR_FS may take a long time on a large system which
  might impair services from serving at their full rated load after
  (re)starting.  Tricks like mremap(2)'ing text onto anonymous memory to
  immediately realize iTLB performance prevents page sharing and demand
  paging, both of which increase steady state memory footprint.  With
  MADV_COLLAPSE, we get the best of both worlds: Peak upfront performance
  and lower RAM footprints.
* Backing guest memory by hugapages after the memory contents have been
  migrated in native-page-sized chunks to a new host, in a
  userfaultfd-based live-migration stack.

[1] https://lore.kernel.org/linux-mm/d098c392-273a-36a4-1a29-59731cdf5d3d@google.com/
[2] https://github.com/google/tcmalloc/tree/master/tcmalloc

[jrdr.linux@gmail.com: avoid possible memory leak in failure path]
  Link: https://lkml.kernel.org/r/20220713024109.62810-1-jrdr.linux@gmail.com
[zokeefe@google.com add missing kfree() to madvise_collapse()]
  Link: https://lore.kernel.org/linux-mm/20220713024109.62810-1-jrdr.linux@gmail.com/
  Link: https://lkml.kernel.org/r/20220713161851.1879439-1-zokeefe@google.com
[zokeefe@google.com: delay computation of hpage boundaries until use]]
  Link: https://lkml.kernel.org/r/20220720140603.1958773-4-zokeefe@google.com
Link: https://lkml.kernel.org/r/20220706235936.2197195-10-zokeefe@google.com
Signed-off-by: Zach O'Keefe 
Signed-off-by: "Souptick Joarder (HPE)" 
Suggested-by: David Rientjes 
Cc: Alex Shi 
Cc: Andrea Arcangeli 
Cc: Arnd Bergmann 
Cc: Axel Rasmussen 
Cc: Chris Kennelly 
Cc: Chris Zankel 
Cc: David Hildenbrand 
Cc: Helge Deller 
Cc: Hugh Dickins 
Cc: Ivan Kokshaysky 
Cc: James Bottomley 
Cc: Jens Axboe 
Cc: "Kirill A. Shutemov" 
Cc: Matthew Wilcox 
Cc: Matt Turner 
Cc: Max Filippov 
Cc: Miaohe Lin 
Cc: Michal Hocko 
Cc: Minchan Kim 
Cc: Pasha Tatashin 
Cc: Pavel Begunkov 
Cc: Peter Xu 
Cc: Rongwei Wang 
Cc: SeongJae Park 
Cc: Song Liu 
Cc: Thomas Bogendoerfer 
Cc: Vlastimil Babka 
Cc: Yang Shi 
Cc: Zi Yan 
Cc: Dan Carpenter 
Signed-off-by: Andrew Morton