From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qt0-f199.google.com (mail-qt0-f199.google.com [209.85.216.199]) by kanga.kvack.org (Postfix) with ESMTP id 01DB26B0006 for ; Mon, 2 Jul 2018 02:42:25 -0400 (EDT) Received: by mail-qt0-f199.google.com with SMTP id f8-v6so17587149qth.9 for ; Sun, 01 Jul 2018 23:42:24 -0700 (PDT) Received: from hqemgate16.nvidia.com (hqemgate16.nvidia.com. [216.228.121.65]) by mx.google.com with ESMTPS id f5-v6si711429qve.92.2018.07.01.23.42.23 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sun, 01 Jul 2018 23:42:24 -0700 (PDT) Subject: Re: [PATCH 2/2] mm: set PG_dma_pinned on get_user_pages*() References: <20180627113221.GO32348@dhcp22.suse.cz> <20180627115349.cu2k3ainqqdrrepz@quack2.suse.cz> <20180627115927.GQ32348@dhcp22.suse.cz> <20180627124255.np2a6rxy6rb6v7mm@quack2.suse.cz> <20180627145718.GB20171@ziepe.ca> <20180627170246.qfvucs72seqabaef@quack2.suse.cz> <1f6e79c5-5801-16d2-18a6-66bd0712b5b8@nvidia.com> <20180628091743.khhta7nafuwstd3m@quack2.suse.cz> <20180702055251.GV3014@mtr-leonro.mtl.com> <235a23e3-6e02-234c-3e20-b2dddc93e568@nvidia.com> <20180702063403.GX3014@mtr-leonro.mtl.com> From: John Hubbard Message-ID: Date: Sun, 1 Jul 2018 23:41:21 -0700 MIME-Version: 1.0 In-Reply-To: <20180702063403.GX3014@mtr-leonro.mtl.com> Content-Type: text/plain; charset="windows-1252" Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Leon Romanovsky Cc: Jan Kara , Jason Gunthorpe , Michal Hocko , Dan Williams , Christoph Hellwig , John Hubbard , Matthew Wilcox , Christopher Lameter , Linux MM , LKML , linux-rdma On 07/01/2018 11:34 PM, Leon Romanovsky wrote: > On Sun, Jul 01, 2018 at 11:10:04PM -0700, John Hubbard wrote: >> On 07/01/2018 10:52 PM, Leon Romanovsky wrote: >>> On Thu, Jun 28, 2018 at 11:17:43AM +0200, Jan Kara wrote: >>>> On Wed 27-06-18 19:42:01, John Hubbard wrote: >>>>> On 06/27/2018 10:02 AM, Jan Kara wrote: >>>>>> On Wed 27-06-18 08:57:18, Jason Gunthorpe wrote: >>>>>>> On Wed, Jun 27, 2018 at 02:42:55PM +0200, Jan Kara wrote: >>>>>>>> On Wed 27-06-18 13:59:27, Michal Hocko wrote: >>>>>>>>> On Wed 27-06-18 13:53:49, Jan Kara wrote: >>>>>>>>>> On Wed 27-06-18 13:32:21, Michal Hocko wrote: >>>>>>>>> [...] >>>>> One question though: I'm still vague on the best actions to take in the >>>>> following functions: >>>>> >>>>> page_mkclean_one >>>>> try_to_unmap_one >>>>> >>>>> At the moment, they are both just doing an evil little early-out: >>>>> >>>>> if (PageDmaPinned(page)) >>>>> return false; >>>>> >>>>> ...but we talked about maybe waiting for the condition to clear, instead? >>>>> Thoughts? >>>> >>>> What needs to happen in page_mkclean() depends on the caller. Most of the >>>> callers really need to be sure the page is write-protected once >>>> page_mkclean() returns. Those are: >>>> >>>> pagecache_isize_extended() >>>> fb_deferred_io_work() >>>> clear_page_dirty_for_io() if called for data-integrity writeback - which >>>> is currently known only in its caller (e.g. write_cache_pages()) where >>>> it can be determined as wbc->sync_mode == WB_SYNC_ALL. Getting this >>>> information into page_mkclean() will require some plumbing and >>>> clear_page_dirty_for_io() has some 50 callers but it's doable. >>>> >>>> clear_page_dirty_for_io() for cleaning writeback (wbc->sync_mode != >>>> WB_SYNC_ALL) can just skip pinned pages and we probably need to do that as >>>> otherwise memory cleaning would get stuck on pinned pages until RDMA >>>> drivers release its pins. >>> >>> Sorry for naive question, but won't it create too much dirty pages >>> so writeback will be called "non-stop" to rebalance watermarks without >>> ability to progress? >>> >> >> That is an interesting point. >> >> Holding off page writeback of this region does seem like it could cause >> problems under memory pressure. Maybe adjusting the watermarks so that we >> tell the writeback system, "all is well, just ignore this region until >> we're done with it" might help? Any ideas here are welcome... > > AFAIR, it is per-zone, so the solution to count dirty-but-untouchable > number of pages to take them into account for accounting can work, but > it seems like an overkill. Can we create special ZONE for such gup > pages, or this is impossible too? > Let's see what Michal and others prefer. The zone idea intrigues me. thanks, -- John Hubbard NVIDIA