The patch titled
Subject: mm/huge_memory: only split PMD mapping when necessary in unmap_folio()
has been added to the -mm mm-unstable branch. Its filename is
mm-huge_memory-only-split-pmd-mapping-when-necessary-in-unmap_folio.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-huge_memory-only-split-pmd-mapping-when-necessary-in-unmap_folio.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Zi Yan <ziy@xxxxxxxxxx>
Subject: mm/huge_memory: only split PMD mapping when necessary in unmap_folio()
Date: Mon, 26 Feb 2024 15:55:27 -0500
Patch series "Split a folio to any lower order folios", v5.
File folio supports any order and multi-size THP is upstreamed[1], so both
file and anonymous folios can be >0 order. Currently, split_huge_page()
only splits a huge page to order-0 pages, but splitting to orders higher
than 0 might better utilize large folios, if done properly. In addition,
Large Block Sizes in XFS support would benefit from it during truncate[2].
This patchset adds support for splitting a large folio to any lower order
folios.
In addition to this implementation of split_huge_page_to_list_to_order(),
a possible optimization could be splitting a large folio to arbitrary
smaller folios instead of a single order. As both Hugh and Ryan pointed
out [3,5] that split to a single order might not be optimal, an order-9
folio might be better split into 1 order-8, 1 order-7, ..., 1 order-1, and
2 order-0 folios, depending on subsequent folio operations. Leave this as
future work.
[1] https://lore.kernel.org/all/20231207161211.2374093-1-ryan.roberts@xxxxxxx/
[2] https://lore.kernel.org/linux-mm/20240226094936.2677493-1-kernel@xxxxxxxxxxxxxxxx/
[3] https://lore.kernel.org/linux-mm/9dd96da-efa2-5123-20d4-4992136ef3ad@xxxxxxxxxx/
[4] https://lore.kernel.org/linux-mm/cbb1d6a0-66dd-47d0-8733-f836fe050374@xxxxxxx/
[5] https://lore.kernel.org/linux-mm/20240213215520.1048625-1-zi.yan@xxxxxxxx/
This patch (of 8):
As multi-size THP support is added, not all THPs are PMD-mapped, thus
during a huge page split, there is no need to always split PMD mapping in
unmap_folio(). Make it conditional.
Link: https://lkml.kernel.org/r/20240226205534.1603748-1-zi.yan@xxxxxxxx
Link: https://lkml.kernel.org/r/20240226205534.1603748-2-zi.yan@xxxxxxxx
Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Luis Chamberlain <mcgrof@xxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Michal Koutny <mkoutny@xxxxxxxx>
Cc: Roman Gushchin <roman.gushchin@xxxxxxxxx>
Cc: Ryan Roberts <ryan.roberts@xxxxxxx>
Cc: Yang Shi <shy828301@xxxxxxxxx>
Cc: Yu Zhao <yuzhao@xxxxxxxxxx>
Cc: Zach O'Keefe <zokeefe@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/huge_memory.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
--- a/mm/huge_memory.c~mm-huge_memory-only-split-pmd-mapping-when-necessary-in-unmap_folio
+++ a/mm/huge_memory.c
@@ -2727,11 +2727,14 @@ void vma_adjust_trans_huge(struct vm_are
static void unmap_folio(struct folio *folio)
{
- enum ttu_flags ttu_flags = TTU_RMAP_LOCKED | TTU_SPLIT_HUGE_PMD |
- TTU_SYNC | TTU_BATCH_FLUSH;
+ enum ttu_flags ttu_flags = TTU_RMAP_LOCKED | TTU_SYNC |
+ TTU_BATCH_FLUSH;
VM_BUG_ON_FOLIO(!folio_test_large(folio), folio);
+ if (folio_test_pmd_mappable(folio))
+ ttu_flags |= TTU_SPLIT_HUGE_PMD;
+
/*
* Anon pages need migration entries to preserve them, but file
* pages can simply be left unmapped, then faulted back on demand.
_
Patches currently in -mm which might be from ziy@xxxxxxxxxx are
mm-huge_memory-only-split-pmd-mapping-when-necessary-in-unmap_folio.patch
mm-memcg-use-order-instead-of-nr-in-split_page_memcg.patch
mm-page_owner-use-order-instead-of-nr-in-split_page_owner.patch
mm-memcg-make-memcg-huge-page-split-support-any-order-split.patch
mm-page_owner-add-support-for-splitting-to-any-order-in-split-page_owner.patch
mm-thp-split-huge-page-to-any-lower-order-pages.patch
mm-huge_memory-enable-debugfs-to-split-huge-pages-to-any-order.patch
