The patch titled
Subject: mm/khugepaged.c: convert VM_BUG_ON() to collapse fail
has been added to the -mm tree. Its filename is
mm-khugepaged-convert-vm_bug_on-to-collapse-fail.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-khugepaged-convert-vm_bug_on-to-collapse-fail.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-khugepaged-convert-vm_bug_on-to-collapse-fail.patch
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/SubmitChecklist when testing your code ***
The -mm tree is included into linux-next and is updated
there every 3-4 working days
------------------------------------------------------
From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
Subject: mm/khugepaged.c: convert VM_BUG_ON() to collapse fail
khugepaged is not yet able to convert PTE-mapped huge pages back to PMD
mapped. We do not collapse such pages. See check khugepaged_scan_pmd().
But if between khugepaged_scan_pmd() and __collapse_huge_page_isolate()
somebody managed to instantiate THP in the range and then split the PMD
back to PTEs we would have a problem -- VM_BUG_ON_PAGE(PageCompound(page))
will get triggered.
It's possible since we drop mmap_sem during collapse to re-take for
write.
Replace the VM_BUG_ON() with graceful collapse fail.
Link: http://lkml.kernel.org/r/20180315152353.27989-1-kirill.shutemov@xxxxxxxxxxxxxxx
Fixes: b1caa957ae6d ("khugepaged: ignore pmd tables with THP mapped with ptes")
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Laura Abbott <labbott@xxxxxxxxxx>
Cc: Jerome Marchand <jmarchan@xxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
diff -puN mm/khugepaged.c~mm-khugepaged-convert-vm_bug_on-to-collapse-fail mm/khugepaged.c
--- a/mm/khugepaged.c~mm-khugepaged-convert-vm_bug_on-to-collapse-fail
+++ a/mm/khugepaged.c
@@ -530,7 +530,12 @@ static int __collapse_huge_page_isolate(
goto out;
}
- VM_BUG_ON_PAGE(PageCompound(page), page);
+ /* TODO: teach khugepaged to collapse THP mapped with pte */
+ if (PageCompound(page)) {
+ result = SCAN_PAGE_COMPOUND;
+ goto out;
+ }
+
VM_BUG_ON_PAGE(!PageAnon(page), page);
/*
_
Patches currently in -mm which might be from kirill.shutemov@xxxxxxxxxxxxxxx are
mm-khugepaged-convert-vm_bug_on-to-collapse-fail.patch
--
To unsubscribe from this list: send the line "unsubscribe mm-commits" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
