The patch titled
Subject: mm/thp: fix "mm: thp: kill __transhuge_page_enabled()"
has been added to the -mm mm-unstable branch. Its filename is
mm-thp-fix-mm-thp-kill-__transhuge_page_enabled.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-thp-fix-mm-thp-kill-__transhuge_page_enabled.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: "Zach O'Keefe" <zokeefe@xxxxxxxxxx>
Subject: mm/thp: fix "mm: thp: kill __transhuge_page_enabled()"
Date: Mon, 25 Sep 2023 13:01:10 -0700
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@xxxxxxxxxx
Fixes: 7da4e2cb8b1f ("mm: thp: kill __transhuge_page_enabled()")
Reported-by: Saurabh Singh Sengar <ssengar@xxxxxxxxxxxxx>
Signed-off-by: Zach O'Keefe <zokeefe@xxxxxxxxxx>
Cc: Yang Shi <shy828301@xxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Ryan Roberts <ryan.roberts@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/huge_memory.c | 20 +++++++++++++-------
1 file changed, 13 insertions(+), 7 deletions(-)
--- a/mm/huge_memory.c~mm-thp-fix-mm-thp-kill-__transhuge_page_enabled
+++ a/mm/huge_memory.c
@@ -100,11 +100,11 @@ bool hugepage_vma_check(struct vm_area_s
return in_pf;
/*
- * Special VMA and hugetlb VMA.
+ * khugepaged special VMA and hugetlb VMA.
* Must be checked after dax since some dax mappings may have
* VM_MIXEDMAP set.
*/
- if (vm_flags & VM_NO_KHUGEPAGED)
+ if (!in_pf && !smaps && (vm_flags & VM_NO_KHUGEPAGED))
return false;
/*
@@ -132,12 +132,18 @@ bool hugepage_vma_check(struct vm_area_s
!hugepage_flags_always())))
return false;
- /* Only regular file is valid */
- if (!in_pf && file_thp_enabled(vma))
- return true;
-
- if (!vma_is_anonymous(vma))
+ if (!vma_is_anonymous(vma)) {
+ /*
+ * Trust that ->huge_fault() handlers know what they are doing
+ * in fault path.
+ */
+ if (((in_pf || smaps)) && vma->vm_ops->huge_fault)
+ return true;
+ /* Only regular file is valid in collapse path */
+ if (((!in_pf || smaps)) && file_thp_enabled(vma))
+ return true;
return false;
+ }
if (vma_is_temporary_stack(vma))
return false;
_
Patches currently in -mm which might be from zokeefe@xxxxxxxxxx are
mm-thp-fix-mm-thp-kill-__transhuge_page_enabled.patch
