From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 78DF3C47404 for ; Wed, 9 Oct 2019 11:00:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 53F4220B7C for ; Wed, 9 Oct 2019 11:00:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729471AbfJILAF (ORCPT ); Wed, 9 Oct 2019 07:00:05 -0400 Received: from foss.arm.com ([217.140.110.172]:59884 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725953AbfJILAF (ORCPT ); Wed, 9 Oct 2019 07:00:05 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 95A0428; Wed, 9 Oct 2019 04:00:04 -0700 (PDT) Received: from [10.1.196.133] (unknown [10.1.196.133]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id E0BA93F703; Wed, 9 Oct 2019 04:00:01 -0700 (PDT) Subject: Re: [PATCH v11 14/22] mm: pagewalk: Add 'depth' parameter to pte_hole To: Jason Gunthorpe Cc: Mark Rutland , Dave Hansen , Arnd Bergmann , Ard Biesheuvel , Peter Zijlstra , Catalin Marinas , x86@kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= , Ingo Molnar , Borislav Petkov , Andy Lutomirski , "H. Peter Anvin" , James Morse , Thomas Gleixner , Will Deacon , Andrew Morton , linux-arm-kernel@lists.infradead.org, "Liang, Kan" References: <20191007153822.16518-1-steven.price@arm.com> <20191007153822.16518-15-steven.price@arm.com> <20191007161049.GA13229@ziepe.ca> <6e570d6d-b29f-f4cb-1eb9-6ff6cab15a2e@arm.com> <20191007181113.GC13229@ziepe.ca> From: Steven Price Message-ID: <7baa4861-eb68-5dcb-137b-482a3b5f52a6@arm.com> Date: Wed, 9 Oct 2019 12:00:00 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.9.0 MIME-Version: 1.0 In-Reply-To: <20191007181113.GC13229@ziepe.ca> Content-Type: text/plain; charset=utf-8 Content-Language: en-GB Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07/10/2019 19:11, Jason Gunthorpe wrote: > On Mon, Oct 07, 2019 at 05:20:30PM +0100, Steven Price wrote: >> On 07/10/2019 17:10, Jason Gunthorpe wrote: >>> On Mon, Oct 07, 2019 at 04:38:14PM +0100, Steven Price wrote: >>>> diff --git a/mm/hmm.c b/mm/hmm.c >>>> index 902f5fa6bf93..34fe904dd417 100644 >>>> +++ b/mm/hmm.c >>>> @@ -376,7 +376,7 @@ static void hmm_range_need_fault(const struct hmm_vma_walk *hmm_vma_walk, >>>> } >>>> >>>> static int hmm_vma_walk_hole(unsigned long addr, unsigned long end, >>>> - struct mm_walk *walk) >>>> + __always_unused int depth, struct mm_walk *walk) >>> >>> It this __always_unused on function arguments something we are doing >>> now? >> >> $ git grep __always_unused | wc -l >> 191 >> >> It's elsewhere in the kernel tree. It seems like a good way of both >> documenting and silencing compiler warnings. But I'm open to other >> suggestions. > > The normal kernel build doesn't generate warnings for unused function > parameters because there are alot of false positives, IIRC. So, seems > weird to see things like this. > >>> Can we have negative depth? Should it be unsigned? >> >> As per the documentation added in this patch: >> >> * @pte_hole: if set, called for each hole at all levels, >> * depth is -1 if not known, 0:PGD, 1:P4D, 2:PUD, 3:PMD >> * 4:PTE. Any folded depths (where PTRS_PER_P?D is equal >> * to 1) are skipped. >> >> So it's signed to allow "-1" in the cases where pte_hole is called >> without knowing the actual depth. This is used in the function >> walk_page_test() because it don't walk the actual page tables, but is >> called on a VMA instead. This means that there may not be a single depth >> for the range provided. > > So are the depth values below OK? I would have expected -1 by this > definition Good spot - that indeed was very sloppy of me. In these cases the value is ignored, but -1 would indeed have been a better value to use. I'll fix that up. Thanks, Steve >>>> { >>>> struct hmm_vma_walk *hmm_vma_walk = walk->private; >>>> struct hmm_range *range = hmm_vma_walk->range; >>>> @@ -564,7 +564,7 @@ static int hmm_vma_walk_pmd(pmd_t *pmdp, >>>> again: >>>> pmd = READ_ONCE(*pmdp); >>>> if (pmd_none(pmd)) >>>> - return hmm_vma_walk_hole(start, end, walk); >>>> + return hmm_vma_walk_hole(start, end, 0, walk); >>>> >>>> if (thp_migration_supported() && is_pmd_migration_entry(pmd)) { >>>> bool fault, write_fault; >>>> @@ -666,7 +666,7 @@ static int hmm_vma_walk_pud(pud_t *pudp, unsigned long start, unsigned long end, >>>> again: >>>> pud = READ_ONCE(*pudp); >>>> if (pud_none(pud)) >>>> - return hmm_vma_walk_hole(start, end, walk); >>>> + return hmm_vma_walk_hole(start, end, 0, walk); >>>> >>>> if (pud_huge(pud) && pud_devmap(pud)) { >>>> unsigned long i, npages, pfn; >>>> @@ -674,7 +674,7 @@ static int hmm_vma_walk_pud(pud_t *pudp, unsigned long start, unsigned long end, >>>> bool fault, write_fault; >>>> >>>> if (!pud_present(pud)) >>>> - return hmm_vma_walk_hole(start, end, walk); >>>> + return hmm_vma_walk_hole(start, end, 0, walk); >>>> >>>> i = (addr - range->start) >> PAGE_SHIFT; >>>> npages = (end - addr) >> PAGE_SHIFT; > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel >