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Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1q2IYF-00FjtV-LU; Thu, 25 May 2023 21:31:15 +0000 Date: Thu, 25 May 2023 22:31:15 +0100 From: Matthew Wilcox To: Steven Sistare Cc: Khalid Aziz , akpm@linux-foundation.org, david@redhat.com, ying.huang@intel.com, mgorman@techsingularity.net, baolin.wang@linux.alibaba.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Khalid Aziz Subject: Re: [PATCH v4] mm, compaction: Skip all non-migratable pages during scan Message-ID: References: <20230525191507.160076-1-khalid.aziz@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: 25FA040014 X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: zcg9ujrbcwr7zui9kb5yj5mbha9go5ht X-HE-Tag: 1685050295-181285 X-HE-Meta: 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 vAo/5GGJ vUZW6vY4iz23X7eLce3mLjTaqwcgO1WofjgLQCIAFsn5LDdcSpYLkJXJx5BLpQlEL/Vzoph7mxaQdbGs44QmOEc6PSudyvTZ7a5DNbaiww7oQ3yx7JZrkLigeW4Ln0NUh2+zF4HHMRCyWKX4= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000104, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu, May 25, 2023 at 09:45:34PM +0100, Matthew Wilcox wrote: > > > Isn't "long term pinning" the wrong description of the problem? Long term > > > pins suggest to me FOLL_LONGTERM. I think this is simple short term > > > pins that we care about here. > > > > vfio pins are held for a long time - Steve > > So this is a third sense of "pinned pages" that is neither what > filesystems nor the mm means by pinned pages, but whatever it is that > vfio means by pinned pages? If only "pin" weren't such a desirable > word. Can somebody explain to me in small words what a vfio pin looks > like because I've tried reading vfio_iommu_type1_pin_pages() and I > don't recognise anything there that looks like pinning in either of > the other two senses. Oh, I think I found it! pin_user_pages_remote() is called by vaddr_get_pfns(). If these are the pages you're concerned about, then the efficient way to do what you want is simply to call folio_maybe_dma_pinned(). Far more efficient than the current mess of total_mapcount().