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Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1q2aY4-002xqz-Qd; Fri, 26 May 2023 16:44:16 +0000 Date: Fri, 26 May 2023 17:44:16 +0100 From: Matthew Wilcox To: Khalid Aziz Cc: Steven Sistare , 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> <60367660-f4a3-06dc-4d17-4dbdc733ef74@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <60367660-f4a3-06dc-4d17-4dbdc733ef74@oracle.com> X-Rspamd-Queue-Id: 7F18D1C0005 X-Rspam-User: X-Rspamd-Server: rspam02 X-Stat-Signature: ebceutyspz714zgyq4ednrahqxmud5by X-HE-Tag: 1685119467-372951 X-HE-Meta: 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 PNU0hH6i bIrkLsKiuq9xsC6wMb2LGR5EZdAtnlIpq2n33f+mq88JgvMApisVcsTJweR0lctCQ6VjZ5fFW8VVVBY59PatUR8BiQ3p4o3UO1Mh1uDSHofpotA4RhWKfTsSW5natcXA7GsWL3TiQ//EGUgpoP4th1WFQDbO0XhvSiCM6 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Fri, May 26, 2023 at 09:44:34AM -0600, Khalid Aziz wrote: > > 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(). > > vfio pinned pages triggered this change. Wouldn't checking refcounts against > mapcount provide a more generalized way of detecting non-migratable pages? Well, you changed the comment to say that we were concerned about long-term pins. If we are, than folio_maybe_dma_pinned() is how to test for long-term pins. If we want to skip pages which are short-term pinned, then we need to not change the comment, and keep using mapcount/refcount differences.