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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?6atzixQVlsmzJ2wHjVIG4BBwj+037v3w8ZjpcqGPKCFZbji3P26xGHpChq4z?= =?us-ascii?Q?SLRkhtcUeNwzQcCwMKJGXnkSa20Lh98j9jUztY4oAEHuq3RAASNAV+NyV2cT?= =?us-ascii?Q?QE5EKR4+V3hGP8D/pz1k1L4wEvwZFW7lTQUgEHeeA0rvhP8gcnAit7sOru9x?= =?us-ascii?Q?juVrSN7HNNtddJcc/T2+HMpDdZr4V+NnuiHhtFZlGf28cl0HuA0v1tw5nrr3?= =?us-ascii?Q?L52jm5G64h5A1+C1N51/dAfelJ3nv5Hj8ZEaNf97GwWBgnzDGDQDWTh58H84?= =?us-ascii?Q?lUL/AJ0F2LCq4cW3IY1p7+cEU3JYdcn60F4zDpZVJtafaxvkCx7Hhf5sdG1G?= =?us-ascii?Q?LlPIa1Qn6d7P+BFXI7LXcFpOOVXcfcFH6sum+iSzW44A2NXnc6OheFVvEIZR?= =?us-ascii?Q?xCwG86TLNuCdFiOmkdUsbI++6jwVBM3Bf7EacowRDPjAF/oZGkxmaUa6NjTg?= =?us-ascii?Q?8stikBCjbXBsyreufSWSvhzK0rRoRFlhBB9TGxWiimyhygaq2LEI/lxDthWH?= =?us-ascii?Q?gL4rognOnYV+JpdtANjRNp7A/wwkMnkemidCtTTvhN7J6m09EZ/6cdteMrLp?= =?us-ascii?Q?VXL6H7nwbj9LJFkyxJwNw05SLFTfIXLuzjRJ31sFY8oZLiyIo35jIkGwTobX?= =?us-ascii?Q?RP9Ll6HOLVnu0CxM7Z7hOnwJx/CB+lywaJ7J7Pyb2n7dGXdeNB4SxpqHRrIJ?= =?us-ascii?Q?/EyE0WBAMEf+ndpZvZgmJCRIY29qzvKb4NDgJD/LzjfjuP/g6J4hIaInEM44?= =?us-ascii?Q?E0aHWrHC9qW5Wz6QCtjQxeFWhIgrEBQ4EJweXxgEy5VaH7uFvuWrF33WKhAh?= =?us-ascii?Q?jEL5tmLraEfacloXiXkGufOXSEG3heeJlAqy0Oy316+gQCBIRUfZFHk4w6uR?= =?us-ascii?Q?BbpU9PNIDylnJpyMnCgOoLtTnXsWgAgrQ2R61Q+V+UEcCTSgJazfsQsCdsX2?= =?us-ascii?Q?HDafkdGUVn8FJNB4VZJWKbSy1isZa8l1+dmrN8AZyVQ6tVeAP5yZvPCYZoZw?= =?us-ascii?Q?UgnlGiPGFptemfR75rFYjQb+Ym2lgExOXF24YdV2bX2fxBc8UBxDKA5fNhp0?= =?us-ascii?Q?TrRRK4CAEJiVX23JPahrqy/OGxYqTZCXAQymNd0ZpvgIBeRsddYGEJYMqDFa?= =?us-ascii?Q?AIfHqWo+1MW73PjK1psxodcQm93HcyO/4dMUSui03iaOBoX52ovpq/Pm2L1O?= =?us-ascii?Q?lXxUseZA/uXWiCkuIzAQ1OEPLUa7DGYNsXKSHbtJ3skSIBHBqF1AC1RhyrWV?= =?us-ascii?Q?utsmUdMMH2UtT+kTiKfgBtjpeDngTiQ0fsljSIy5zV7QVSiO/UtJdRG9OLFh?= =?us-ascii?Q?FoY+/5n7kFsaokamkWhA8lJIfq48tAWLgAFEaFbXTjh5WQ=3D=3D?= X-MS-Exchange-CrossTenant-Network-Message-Id: ba4bac41-49b4-4017-78f6-08d962033ec7 X-MS-Exchange-CrossTenant-AuthSource: BYAPR15MB4136.namprd15.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 18 Aug 2021 04:47:12.8029 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 8ae927fe-1255-47a7-a2af-5f3a069daaa2 X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: JpuFKsDHMwnGSkvwT81/1ftBLhk3Vfm4FQZw6C/84VUDY610ckjzBHavR7p9g2IM X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR15MB2279 X-OriginatorOrg: fb.com X-Proofpoint-GUID: Uc7QeG-izrRBOY50Iu9G_wgvSVIcNAGi X-Proofpoint-ORIG-GUID: Uc7QeG-izrRBOY50Iu9G_wgvSVIcNAGi X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.391,18.0.790 definitions=2021-08-18_01:2021-08-17,2021-08-18 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 mlxscore=0 suspectscore=0 bulkscore=0 malwarescore=0 adultscore=0 spamscore=0 impostorscore=0 priorityscore=1501 mlxlogscore=999 clxscore=1015 phishscore=0 lowpriorityscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2107140000 definitions=main-2108180029 X-FB-Internal: deliver Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Aug 18, 2021 at 12:28:02PM +0800, Muchun Song wrote: > On Wed, Aug 18, 2021 at 11:18 AM Roman Gushchin wrote: > > > > On Sat, Aug 14, 2021 at 01:25:10PM +0800, Muchun Song wrote: > > > The diagram below shows how to make the folio lruvec lock safe when LRU > > > pages are reparented. > > > > > > folio_lruvec_lock(folio) > > > retry: > > > lruvec = folio_lruvec(folio); > > > > > > // The folio is reparented at this time. > > > spin_lock(&lruvec->lru_lock); > > > > > > if (unlikely(lruvec_memcg(lruvec) != folio_memcg(folio))) > > > // Acquired the wrong lruvec lock and need to retry. > > > // Because this folio is on the parent memcg lruvec list. > > > goto retry; > > > > > > // If we reach here, it means that folio_memcg(folio) is stable. > > > > > > memcg_reparent_objcgs(memcg) > > > // lruvec belongs to memcg and lruvec_parent belongs to parent memcg. > > > spin_lock(&lruvec->lru_lock); > > > spin_lock(&lruvec_parent->lru_lock); > > > > > > // Move all the pages from the lruvec list to the parent lruvec list. > > > > > > spin_unlock(&lruvec_parent->lru_lock); > > > spin_unlock(&lruvec->lru_lock); > > > > > > After we acquire the lruvec lock, we need to check whether the folio is > > > reparented. If so, we need to reacquire the new lruvec lock. On the > > > routine of the LRU pages reparenting, we will also acquire the lruvec > > > lock (will be implemented in the later patch). So folio_memcg() cannot > > > be changed when we hold the lruvec lock. > > > > > > Since lruvec_memcg(lruvec) is always equal to folio_memcg(folio) after > > > we hold the lruvec lock, lruvec_memcg_debug() check is pointless. So > > > remove it. > > > > > > This is a preparation for reparenting the LRU pages. > > > > > > Signed-off-by: Muchun Song > > > Acked-by: Roman Gushchin > > > > Maybe it's mostly s/page/folio, but the patch looks quite differently > > in comparison to the version I did ack. In general, please, drop acks > > when there are significant changes between versions. > > Got it. I'll drop all acks in the next version. Thanks. Thank you! The code look correct though. But the locking scheme becomes very complicated (it was already complex). I wonder if there are better ideas. No ideas out of my head, need to think more. If not, your approach looks ok.