From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-yw0-f200.google.com (mail-yw0-f200.google.com [209.85.161.200]) by kanga.kvack.org (Postfix) with ESMTP id 60CBC6B027B for ; Mon, 9 Jul 2018 04:06:33 -0400 (EDT) Received: by mail-yw0-f200.google.com with SMTP id r144-v6so8297556ywg.9 for ; Mon, 09 Jul 2018 01:06:33 -0700 (PDT) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id n125-v6sor1167974ybb.59.2018.07.09.01.06.32 for (Google Transport Security); Mon, 09 Jul 2018 01:06:32 -0700 (PDT) From: john.hubbard@gmail.com Subject: [PATCH 0/2] mm/fs: put_user_page() proposal Date: Mon, 9 Jul 2018 01:05:52 -0700 Message-Id: <20180709080554.21931-1-jhubbard@nvidia.com> Sender: owner-linux-mm@kvack.org List-ID: To: Matthew Wilcox , Michal Hocko , Christopher Lameter , Jason Gunthorpe , Dan Williams , Jan Kara , Al Viro Cc: linux-mm@kvack.org, LKML , linux-rdma , linux-fsdevel@vger.kernel.org, John Hubbard From: John Hubbard Hi, With respect to tracking get_user_pages*() pages with page->dma_pinned* fields [1], I spent a few days retrofitting most of the get_user_pages*() call sites, by adding calls to a new put_user_page() function, in place of put_page(), where appropriate. This will work, but it's a large effort. Design note: I didn't see anything that hinted at a way to fix this problem, without actually changing all of the get_user_pages*() call sites, so I think it's reasonable to start with that. Anyway, it's still incomplete, but because this is a large, tree-wide change (that will take some time and testing), I'd like to propose a plan, before spamming zillions of people with put_user_page() conversion patches. So I picked out the first two patches to show where this is going. Proposed steps: Step 1: Start with the patches here, then continue with...dozens more. This will eventually convert all of the call sites to use put_user_page(). This is easy in some places, but complex in others, such as: -- drivers/gpu/drm/amd -- bio -- fuse -- cifs -- anything from: git grep iov_iter_get_pages | cut -f1 -d ':' | sort | uniq The easy ones can be grouped into a single patchset, perhaps, and the complex ones probably each need a patchset, in order to get the in-depth review they'll need. Furthermore, some of these areas I hope to attract some help on, once this starts going. Step 2: In parallel, tidy up the core patchset that was discussed in [1], (version 2 has already been reviewed, so I know what to do), and get it perfected and reviewed. Don't apply it until step 1 is all done, though. Step 3: Activate refcounting of dma-pinned pages (essentially, patch #5, which is [1]), but don't use it yet. Place a few WARN_ON_ONCE calls to start mopping up any missed call sites. Step 4: After some soak time, actually connect it up (patch #6 of [1]) and start taking action based on the new page->dma_pinned* fields. [1] https://www.spinics.net/lists/linux-mm/msg156409.html or, the same thread on LKML if it's working for you: https://lkml.org/lkml/2018/7/4/368 John Hubbard (2): mm: introduce put_user_page(), placeholder version goldfish_pipe/mm: convert to the new put_user_page() call drivers/platform/goldfish/goldfish_pipe.c | 6 +++--- include/linux/mm.h | 14 ++++++++++++++ 2 files changed, 17 insertions(+), 3 deletions(-) -- 2.18.0