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Thunderbird/102.11.0 Subject: Re: [PATCH v4] mm, compaction: Skip all non-migratable pages during scan To: Matthew Wilcox , Steven Sistare Cc: 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 References: <20230525191507.160076-1-khalid.aziz@oracle.com> Content-Language: en-US From: Khalid Aziz In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: BYAPR21CA0026.namprd21.prod.outlook.com (2603:10b6:a03:114::36) To CH3PR10MB6810.namprd10.prod.outlook.com (2603:10b6:610:140::15) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CH3PR10MB6810:EE_|MN2PR10MB4318:EE_ X-MS-Office365-Filtering-Correlation-Id: 756d4947-5918-4f7c-a1f4-08db5e001c0e X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; 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X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.254,Aquarius:18.0.957,Hydra:6.0.573,FMLib:17.11.176.26 definitions=2023-05-26_06,2023-05-25_03,2023-05-22_02 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 adultscore=0 phishscore=0 mlxscore=0 mlxlogscore=999 bulkscore=0 malwarescore=0 suspectscore=0 spamscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2304280000 definitions=main-2305260133 X-Proofpoint-ORIG-GUID: Zsl-_67mWvgPN0Y5uIizsHr5hVpqVOjU X-Proofpoint-GUID: Zsl-_67mWvgPN0Y5uIizsHr5hVpqVOjU Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 5/25/23 15:31, Matthew Wilcox wrote: > 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(). vfio pinned pages triggered this change. Wouldn't checking refcounts against mapcount provide a more generalized way of detecting non-migratable pages? Thanks, Khalid