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Date: Sat, 21 Dec 2019 15:59:24 -0800 From: John Hubbard <jhubbard@...dia.com> To: Leon Romanovsky <leon@...nel.org> CC: Jason Gunthorpe <jgg@...pe.ca>, Andrew Morton <akpm@...ux-foundation.org>, Al Viro <viro@...iv.linux.org.uk>, Alex Williamson <alex.williamson@...hat.com>, Benjamin Herrenschmidt <benh@...nel.crashing.org>, Björn Töpel <bjorn.topel@...el.com>, Christoph Hellwig <hch@...radead.org>, Dan Williams <dan.j.williams@...el.com>, Daniel Vetter <daniel@...ll.ch>, Dave Chinner <david@...morbit.com>, David Airlie <airlied@...ux.ie>, "David S . Miller" <davem@...emloft.net>, Ira Weiny <ira.weiny@...el.com>, Jan Kara <jack@...e.cz>, Jens Axboe <axboe@...nel.dk>, Jonathan Corbet <corbet@....net>, Jérôme Glisse <jglisse@...hat.com>, Magnus Karlsson <magnus.karlsson@...el.com>, Mauro Carvalho Chehab <mchehab@...nel.org>, Michael Ellerman <mpe@...erman.id.au>, Michal Hocko <mhocko@...e.com>, Mike Kravetz <mike.kravetz@...cle.com>, Paul Mackerras <paulus@...ba.org>, Shuah Khan <shuah@...nel.org>, Vlastimil Babka <vbabka@...e.cz>, <bpf@...r.kernel.org>, <dri-devel@...ts.freedesktop.org>, <kvm@...r.kernel.org>, <linux-block@...r.kernel.org>, <linux-doc@...r.kernel.org>, <linux-fsdevel@...r.kernel.org>, <linux-kselftest@...r.kernel.org>, <linux-media@...r.kernel.org>, <linux-rdma@...r.kernel.org>, <linuxppc-dev@...ts.ozlabs.org>, <netdev@...r.kernel.org>, <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>, Maor Gottlieb <maorg@...lanox.com> Subject: Re: [PATCH v11 00/25] mm/gup: track dma-pinned pages: FOLL_PIN On 12/21/19 2:08 AM, Leon Romanovsky wrote: > On Fri, Dec 20, 2019 at 03:54:55PM -0800, John Hubbard wrote: >> On 12/20/19 10:29 AM, Leon Romanovsky wrote: >> ... >>>> $ ./build.sh >>>> $ build/bin/run_tests.py >>>> >>>> If you get things that far I think Leon can get a reproduction for you >>> >>> I'm not so optimistic about that. >>> >> >> OK, I'm going to proceed for now on the assumption that I've got an overflow >> problem that happens when huge pages are pinned. If I can get more information, >> great, otherwise it's probably enough. >> >> One thing: for your repro, if you know the huge page size, and the system >> page size for that case, that would really help. Also the number of pins per >> page, more or less, that you'd expect. Because Jason says that only 2M huge >> pages are used... >> >> Because the other possibility is that the refcount really is going negative, >> likely due to a mismatched pin/unpin somehow. >> >> If there's not an obvious repro case available, but you do have one (is it easy >> to repro, though?), then *if* you have the time, I could point you to a github >> branch that reduces GUP_PIN_COUNTING_BIAS by, say, 4x, by applying this: > > I'll see what I can do this Sunday. > The other data point that might shed light on whether it's a mismatch (this only works if the system is not actually crashing, though), is checking the new vmstat items, like this: $ grep foll_pin /proc/vmstat nr_foll_pin_requested 16288188 nr_foll_pin_returned 16288188 ...but OTOH, if you've got long-term pins, then those are *supposed* to be mismatched, so it only really helps in between tests. thanks, -- John Hubbard NVIDIA
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