Messages in this thread | | | From | Punit Agrawal <> | Subject | [PATCH 0/1] Clarify huge_pte_offset() semantics | Date | Tue, 25 Jul 2017 16:41:13 +0100 |
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Hi,
The following patch is an attempt to make huge_pte_offset() consistent when dealing with different levels of the page table and document the expected semantics. Previously posting can be found at [0].
Changelog
RFC - v1 * Merge Patch 1 and 2 - preserve bisectability * Drop RFC tag
Original cover letter follows...
The generic implementation of huge_pte_offset() has inconsistent behaviour when looking up hugepage PUDs vs PMDs entries that are not present (returning NULL vs pte_t*).
Similarly, it returns NULL when encountering swap entries although all the callers have special checks to properly deal with swap entries.
Without clear semantics, it is difficult to determine if a change breaks huge_pte_offset() without going through all the scenarios where it is used.
I faced this recently when updating the arm64 implementation of huge_pte_offset() to handle swap entries (related to enabling poisoned memeory)[1]. And will come across again when I update it for contiguous hugepage support now that core changes have been merged.
To address these issues, this following patch -
* makes huge_pte_offset() consistent between PUD and PMDs * and, documents the expected behaviour of huge_pte_offset()
All feedback welcome.
Thanks, Punit
[0] https://lkml.org/lkml/2017/7/24/514 [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=f02ab08afbe76ee7b0b2a34a9970e7dd200d8b01
Punit Agrawal (1): mm/hugetlb: Make huge_pte_offset() consistent and document behaviour
mm/hugetlb.c | 22 +++++++++++++++++++--- 1 file changed, 19 insertions(+), 3 deletions(-)
-- 2.11.0
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