From mboxrd@z Thu Jan 1 00:00:00 1970 From: Punit Agrawal Subject: [PATCH 0/1] Clarify huge_pte_offset() semantics Date: Tue, 25 Jul 2017 16:41:13 +0100 Message-ID: <20170725154114.24131-1-punit.agrawal@arm.com> Return-path: Received: from foss.arm.com ([217.140.101.70]:49646 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752304AbdGYPl1 (ORCPT ); Tue, 25 Jul 2017 11:41:27 -0400 Sender: linux-arch-owner@vger.kernel.org List-ID: To: Andrew Morton Cc: Punit Agrawal , Naoya Horiguchi , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, steve.capper@arm.com, will.deacon@arm.com, catalin.marinas@arm.com, kirill.shutemov@linux.intel.com, Michal Hocko , Mike Kravetz 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