From: Leon Romanovsky <leon@kernel.org>
To: Jan Kara <jack@suse.cz>
Cc: John Hubbard <jhubbard@nvidia.com>,
Jason Gunthorpe <jgg@ziepe.ca>, Michal Hocko <mhocko@kernel.org>,
Dan Williams <dan.j.williams@intel.com>,
Christoph Hellwig <hch@lst.de>,
John Hubbard <john.hubbard@gmail.com>,
Matthew Wilcox <willy@infradead.org>,
Christopher Lameter <cl@linux.com>, Linux MM <linux-mm@kvack.org>,
LKML <linux-kernel@vger.kernel.org>,
linux-rdma <linux-rdma@vger.kernel.org>
Subject: Re: [PATCH 2/2] mm: set PG_dma_pinned on get_user_pages*()
Date: Mon, 2 Jul 2018 08:52:51 +0300 [thread overview]
Message-ID: <20180702055251.GV3014@mtr-leonro.mtl.com> (raw)
In-Reply-To: <20180628091743.khhta7nafuwstd3m@quack2.suse.cz>
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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:
> > >>>> [...]
> > >>>>>> Appart from that, do we really care about 32b here? Big DIO, IB users
> > >>>>>> seem to be 64b only AFAIU.
> > >>>>>
> > >>>>> IMO it is a bad habit to leave unpriviledged-user-triggerable oops in the
> > >>>>> kernel even for uncommon platforms...
> > >>>>
> > >>>> Absolutely agreed! I didn't mean to keep the blow up for 32b. I just
> > >>>> wanted to say that we can stay with a simple solution for 32b. I thought
> > >>>> the g-u-p-longterm has plugged the most obvious breakage already. But
> > >>>> maybe I just misunderstood.
> > >>>
> > >>> Most yes, but if you try hard enough, you can still trigger the oops e.g.
> > >>> with appropriately set up direct IO when racing with writeback / reclaim.
> > >>
> > >> gup longterm is only different from normal gup if you have DAX and few
> > >> people do, which really means it doesn't help at all.. AFAIK??
> > >
> > > Right, what I wrote works only for DAX. For non-DAX situation g-u-p
> > > longterm does not currently help at all. Sorry for confusion.
> > >
> >
> > OK, I've got an early version of this up and running, reusing the page->lru
> > fields. I'll clean it up and do some heavier testing, and post as a PATCH v2.
>
> Cool.
>
> > 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?
Thanks
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next prev parent reply other threads:[~2018-07-02 5:52 UTC|newest]
Thread overview: 57+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-06-17 1:25 [PATCH 0/2] mm: gup: don't unmap or drop filesystem buffers john.hubbard
2018-06-17 1:25 ` [PATCH 1/2] consolidate get_user_pages error handling john.hubbard
2018-06-17 1:25 ` [PATCH 2/2] mm: set PG_dma_pinned on get_user_pages*() john.hubbard
2018-06-17 19:53 ` Dan Williams
2018-06-17 20:04 ` Jason Gunthorpe
2018-06-17 20:10 ` Dan Williams
2018-06-17 20:28 ` John Hubbard
2018-06-18 8:12 ` Christoph Hellwig
2018-06-18 17:50 ` John Hubbard
2018-06-18 17:56 ` Dan Williams
2018-06-18 18:14 ` John Hubbard
2018-06-18 19:21 ` Dan Williams
2018-06-18 19:31 ` Jason Gunthorpe
2018-06-18 20:04 ` Dan Williams
2018-06-18 21:36 ` John Hubbard
2018-06-19 8:29 ` Jan Kara
2018-06-19 9:02 ` Matthew Wilcox
2018-06-19 10:41 ` Jan Kara
2018-06-19 18:11 ` John Hubbard
2018-06-20 1:24 ` Dan Williams
2018-06-20 1:34 ` John Hubbard
2018-06-20 1:57 ` Dan Williams
2018-06-20 2:03 ` John Hubbard
2018-06-20 12:08 ` Jan Kara
2018-06-20 22:55 ` John Hubbard
2018-06-21 16:30 ` Jan Kara
2018-06-25 15:21 ` Jan Kara
2018-06-25 19:03 ` John Hubbard
2018-06-26 7:52 ` Jan Kara
2018-06-26 6:31 ` John Hubbard
2018-06-26 11:48 ` Jan Kara
2018-06-26 13:47 ` Michal Hocko
2018-06-26 16:48 ` Jan Kara
2018-06-27 11:32 ` Michal Hocko
2018-06-27 11:53 ` Jan Kara
2018-06-27 11:59 ` Michal Hocko
2018-06-27 12:42 ` Jan Kara
2018-06-27 14:57 ` Jason Gunthorpe
2018-06-27 17:02 ` Jan Kara
2018-06-28 2:42 ` John Hubbard
2018-06-28 9:17 ` Jan Kara
2018-07-02 5:52 ` Leon Romanovsky [this message]
2018-07-02 6:10 ` John Hubbard
2018-07-02 6:34 ` Leon Romanovsky
2018-07-02 6:41 ` John Hubbard
2018-07-02 10:36 ` Michal Hocko
2018-07-02 7:02 ` Jan Kara
2018-07-02 14:48 ` Michal Hocko
2018-07-02 6:58 ` Jan Kara
2018-06-18 8:11 ` Christoph Hellwig
2018-06-19 6:15 ` Leon Romanovsky
2018-06-17 22:19 ` John Hubbard
2018-06-18 7:56 ` Christoph Hellwig
2018-06-18 17:44 ` John Hubbard
2018-06-17 21:54 ` [PATCH 0/2] mm: gup: don't unmap or drop filesystem buffers Christopher Lameter
2018-06-17 22:23 ` John Hubbard
2018-06-18 8:10 ` Christoph Hellwig
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