From: Zi Yan ziy@nvidia.com
mainline inclusion from mainline-v6.9-rc1 commit 319a624ec2b79db7a0b0a2a2a61e3aa5c96eabfc category: feature bugzilla: https://gitee.com/openeuler/kernel/issues/I9OCYO CVE: NA
Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i...
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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@arm.com/ [2] https://lore.kernel.org/linux-mm/20240226094936.2677493-1-kernel@pankajragha... [3] https://lore.kernel.org/linux-mm/9dd96da-efa2-5123-20d4-4992136ef3ad@google.... [4] https://lore.kernel.org/linux-mm/cbb1d6a0-66dd-47d0-8733-f836fe050374@arm.co... [5] https://lore.kernel.org/linux-mm/20240213215520.1048625-1-zi.yan@sent.com/
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@sent.com Link: https://lkml.kernel.org/r/20240226205534.1603748-2-zi.yan@sent.com Signed-off-by: Zi Yan ziy@nvidia.com Reviewed-by: David Hildenbrand david@redhat.com Cc: Hugh Dickins hughd@google.com Cc: Kirill A. Shutemov kirill.shutemov@linux.intel.com Cc: Luis Chamberlain mcgrof@kernel.org Cc: Matthew Wilcox willy@infradead.org Cc: Michal Koutny mkoutny@suse.com Cc: Roman Gushchin roman.gushchin@linux.dev Cc: Ryan Roberts ryan.roberts@arm.com Cc: Yang Shi shy828301@gmail.com Cc: Yu Zhao yuzhao@google.com Cc: Zach O'Keefe zokeefe@google.com Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Liu Shixin liushixin2@huawei.com --- mm/huge_memory.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/mm/huge_memory.c b/mm/huge_memory.c index b41f3d607c67..21ec24a6658b 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -2594,11 +2594,14 @@ void vma_adjust_trans_huge(struct vm_area_struct *vma,
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.