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[142.162.113.180]) by smtp.gmail.com with ESMTPSA id s17sm7755821qkg.79.2019.10.07.11.11.14 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Mon, 07 Oct 2019 11:11:14 -0700 (PDT) Received: from jgg by mlx.ziepe.ca with local (Exim 4.90_1) (envelope-from ) id 1iHXTV-0007lh-Lt; Mon, 07 Oct 2019 15:11:13 -0300 Date: Mon, 7 Oct 2019 15:11:13 -0300 From: Jason Gunthorpe To: Steven Price Cc: Mark Rutland , x86@kernel.org, Arnd Bergmann , Ard Biesheuvel , Peter Zijlstra , Catalin Marinas , Dave Hansen , linux-kernel@vger.kernel.org, linux-mm@kvack.org, =?utf-8?B?SsOpcsO0bWU=?= Glisse , 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" Subject: Re: [PATCH v11 14/22] mm: pagewalk: Add 'depth' parameter to pte_hole Message-ID: <20191007181113.GC13229@ziepe.ca> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <6e570d6d-b29f-f4cb-1eb9-6ff6cab15a2e@arm.com> User-Agent: Mutt/1.9.4 (2018-02-28) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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 > >> { > >> 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;