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[213.95.11.211]) by mx.google.com with ESMTPS id j3si44760436wrs.215.2019.07.23.23.51.47 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 23 Jul 2019 23:51:47 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of hch@lst.de designates 213.95.11.211 as permitted sender) client-ip=213.95.11.211; Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of hch@lst.de designates 213.95.11.211 as permitted sender) smtp.mailfrom=hch@lst.de Received: by verein.lst.de (Postfix, from userid 2407) id 6DD4768B02; Wed, 24 Jul 2019 08:51:46 +0200 (CEST) Date: Wed, 24 Jul 2019 08:51:46 +0200 From: Christoph Hellwig To: Ralph Campbell Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, =?iso-8859-1?B?Suly9G1l?= Glisse , Jason Gunthorpe , Christoph Hellwig Subject: Re: [PATCH 2/2] mm/hmm: make full use of walk_page_range() Message-ID: <20190724065146.GA2061@lst.de> References: <20190723233016.26403-1-rcampbell@nvidia.com> <20190723233016.26403-3-rcampbell@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190723233016.26403-3-rcampbell@nvidia.com> User-Agent: Mutt/1.5.17 (2007-11-01) 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 Tue, Jul 23, 2019 at 04:30:16PM -0700, Ralph Campbell wrote: > hmm_range_snapshot() and hmm_range_fault() both call find_vma() and > walk_page_range() in a loop. This is unnecessary duplication since > walk_page_range() calls find_vma() in a loop already. > Simplify hmm_range_snapshot() and hmm_range_fault() by defining a > walk_test() callback function to filter unhandled vmas. I like the approach a lot! But we really need to sort out the duplication between hmm_range_fault and hmm_range_snapshot first, as they are basically the same code. I have patches here: http://git.infradead.org/users/hch/misc.git/commitdiff/a34ccd30ee8a8a3111d9e91711c12901ed7dea74 http://git.infradead.org/users/hch/misc.git/commitdiff/81f442ebac7170815af7770a1efa9c4ab662137e That being said we don't really have any users for the snapshot mode or non-blocking faults, and I don't see any in the immediate pipeline either. It might actually be a better idea to just kill that stuff off for now until we have a user, as code without users is per definition untested and will just bitrot and break. > + const unsigned long device_vma = VM_IO | VM_PFNMAP | VM_MIXEDMAP; > + struct hmm_vma_walk *hmm_vma_walk = walk->private; > + struct hmm_range *range = hmm_vma_walk->range; > + struct vm_area_struct *vma = walk->vma; > + > + /* If range is no longer valid, force retry. */ > + if (!range->valid) > + return -EBUSY; > + > + if (vma->vm_flags & device_vma) Can we just kill off this odd device_vma variable? if (vma->vm_flags & (VM_IO | VM_PFNMAP | VM_MIXEDMAP)) and maybe add a comment on why we are skipping them (because they don't have struct page backing I guess..)