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zhang.lyra@gmail.com, gerald.schaefer@linux.ibm.com, vishal.l.verma@intel.com, dave.jiang@intel.com, logang@deltatee.com, bhelgaas@google.com, jack@suse.cz, jgg@ziepe.ca, catalin.marinas@arm.com, will@kernel.org, mpe@ellerman.id.au, npiggin@gmail.com, dave.hansen@linux.intel.com, ira.weiny@intel.com, willy@infradead.org, djwong@kernel.org, tytso@mit.edu, linmiaohe@huawei.com, peterx@redhat.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, nvdimm@lists.linux.dev, linux-cxl@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, linux-xfs@vger.kernel.org, jhubbard@nvidia.com, hch@lst.de, david@fromorbit.com, akpm@linux-foundation.org, sfr@canb.auug.org.au Subject: Re: [PATCH v3 00/25] fs/dax: Fix ZONE_DEVICE page reference counts Message-ID: References: <675ce1e5a3d68_fad0294d0@dwillia2-xfh.jf.intel.com.notmuch> <45555f72-e82a-4196-94af-22d05d6ac947@redhat.com> Content-Type: text/plain; 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 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: List-Subscribe: List-Unsubscribe: On Sat, Dec 14, 2024 at 04:22:58PM +0100, David Hildenbrand wrote: > On 14.12.24 02:39, Dan Williams wrote: > > [ add akpm and sfr for next steps ] > > > > Alistair Popple wrote: > > > Main updates since v2: > > > > > > - Rename the DAX specific dax_insert_XXX functions to vmf_insert_XXX > > > and have them pass the vmf struct. > > > > > > - Seperate out the device DAX changes. > > > > > > - Restore the page share mapping counting and associated warnings. > > > > > > - Rework truncate to require file-systems to have previously called > > > dax_break_layout() to remove the address space mapping for a > > > page. This found several bugs which are fixed by the first half of > > > the series. The motivation for this was initially to allow the FS > > > DAX page-cache mappings to hold a reference on the page. > > > > > > However that turned out to be a dead-end (see the comments on patch > > > 21), but it found several bugs and I think overall it is an > > > improvement so I have left it here. > > > > > > Device and FS DAX pages have always maintained their own page > > > reference counts without following the normal rules for page reference > > > counting. In particular pages are considered free when the refcount > > > hits one rather than zero and refcounts are not added when mapping the > > > page. > > > > > > Tracking this requires special PTE bits (PTE_DEVMAP) and a secondary > > > mechanism for allowing GUP to hold references on the page (see > > > get_dev_pagemap). However there doesn't seem to be any reason why FS > > > DAX pages need their own reference counting scheme. > > > > > > By treating the refcounts on these pages the same way as normal pages > > > we can remove a lot of special checks. In particular pXd_trans_huge() > > > becomes the same as pXd_leaf(), although I haven't made that change > > > here. It also frees up a valuable SW define PTE bit on architectures > > > that have devmap PTE bits defined. > > > > > > It also almost certainly allows further clean-up of the devmap managed > > > functions, but I have left that as a future improvment. It also > > > enables support for compound ZONE_DEVICE pages which is one of my > > > primary motivators for doing this work. > > > > So this is feeling ready for -next exposure, and ideally merged for v6.14. I > > see the comments from John and Bjorn and that you were going to respin for > > that, but if it's just those details things they can probably be handled > > incrementally. > > > > Alistair, are you ready for this to hit -next? Yeah, I'm pretty happy with the series now. It "feels" right. There's a couple of dumb build bot errors, so I was going to respin to fix those as well. I got caught up with a few other things so was just letting this sit awaiting feedback, but I should be able to post a respin early this week. > > As for which tree... > > > > Andrew, we could take this through -mm, but my first instinct would be to try > > to take it through nvdimm.git mainly to offload any conflict wrangling work and > > small fixups which are likely to be an ongoing trickle. > > > > However, I am not going to put up much of a fight if others prefer this go > > through -mm. > > > > Thoughts? > > I'm in the process of preparing v2 of [1] that will result in conflicts with > this series in the rmap code (in particular [PATCH v3 14/25] huge_memory: > Allow mappings of PUD sized pages). > > I'll be away for 2 weeks over Christmas, but I assume I'll manage to post v2 > shortly. > > Which reminds me that I still have to take a closer look at some things in > this series :) Especially also #14 regarding accounting. > > I wonder if we could split out the rmap changes in #14, and have that patch > simply in two trees? No idea. I could split out the first half (patches 1 - 8) into a series to go via nvdimm.git, because they are actually standalone clean ups that I think are worthwhile anyway. The remainder are more -mm focussed. However they do depend on the fs/dax cleanups in the first half so the trick would be making sure Andrew only takes them if the nvdimm.git changes have made it into -next. I'm happy with either approach, so let me know if I should split the series or not. - Alistair > [1] > https://lore.kernel.org/all/20240829165627.2256514-1-david@redhat.com/T/#u > > -- > Cheers, > > David / dhildenb >