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Date: Thu, 2 May 2024 19:44:58 +0100
From: Matthew Wilcox <willy@infradead.org>
To: Jason Gunthorpe <jgg@nvidia.com>
Cc: John Hubbard <jhubbard@nvidia.com>,
	David Hildenbrand <david@redhat.com>,
	Alistair Popple <apopple@nvidia.com>,
	Christoph Hellwig <hch@infradead.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	LKML <linux-kernel@vger.kernel.org>, linux-rdma@vger.kernel.org,
	linux-mm@kvack.org, Mike Marciniszyn <mike.marciniszyn@intel.com>,
	Leon Romanovsky <leon@kernel.org>,
	Artemy Kovalyov <artemyko@nvidia.com>,
	Michael Guralnik <michaelgur@nvidia.com>,
	Pak Markthub <pmarkthub@nvidia.com>
Subject: Re: [RFC] RDMA/umem: pin_user_pages*() can temporarily fail due to
 migration glitches
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On Thu, May 02, 2024 at 03:34:08PM -0300, Jason Gunthorpe wrote:
> IMHO pin_user_pages() should sleep and spin in an interruptable sleep

killable, not interruptible.  Otherwise SIGWINCH and SIGALRM can
result an early return.

> until we get all the migrations done. Not sure how hard it would be to
> add some kind of proper waiting event sleep?

ummmmm.  We have a "has waiters" bit in the folio.  So on every call to
folio_put(), we could check that bit and wake up any waiters.  I need to
think about that; right now, we only use it for unlock and end_writeback.
Making folio_put() heavier is, well, quite a lot of call-sites.