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H A D | huge_memory.c | diff 7a81751fcdeb833acc858e59082688e3020bfe12 Mon Sep 25 22:01:10 CEST 2023 Zach O'Keefe <zokeefe@google.com> mm/thp: fix "mm: thp: kill __transhuge_page_enabled()"
The 6.0 commits:
commit 9fec51689ff6 ("mm: thp: kill transparent_hugepage_active()") commit 7da4e2cb8b1f ("mm: thp: kill __transhuge_page_enabled()")
merged "can we have THPs in this VMA?" logic that was previously done separately by fault-path, khugepaged, and smaps "THPeligible" checks.
During the process, the semantics of the fault path check changed in two ways:
1) A VM_NO_KHUGEPAGED check was introduced (also added to smaps path). 2) We no longer checked if non-anonymous memory had a vm_ops->huge_fault handler that could satisfy the fault. Previously, this check had been done in create_huge_pud() and create_huge_pmd() routines, but after the changes, we never reach those routines.
During the review of the above commits, it was determined that in-tree users weren't affected by the change; most notably, since the only relevant user (in terms of THP) of VM_MIXEDMAP or ->huge_fault is DAX, which is explicitly approved early in approval logic. However, this was a bad assumption to make as it assumes the only reason to support ->huge_fault was for DAX (which is not true in general).
Remove the VM_NO_KHUGEPAGED check when not in collapse path and give any ->huge_fault handler a chance to handle the fault. Note that we don't validate the file mode or mapping alignment, which is consistent with the behavior before the aforementioned commits.
Link: https://lkml.kernel.org/r/20230925200110.1979606-1-zokeefe@google.com Fixes: 7da4e2cb8b1f ("mm: thp: kill __transhuge_page_enabled()") Reported-by: Saurabh Singh Sengar <ssengar@microsoft.com> Signed-off-by: Zach O'Keefe <zokeefe@google.com> Cc: Yang Shi <shy828301@gmail.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: David Hildenbrand <david@redhat.com> Cc: Ryan Roberts <ryan.roberts@arm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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