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Fri, 15 May 2020 22:12:58 +0000 Date: Fri, 15 May 2020 15:12:55 -0700 From: Roman Gushchin To: Christopher Lameter CC: Andrew Morton , Johannes Weiner , Michal Hocko , , , Subject: Re: [PATCH v3 04/19] mm: slub: implement SLUB version of obj_to_index() Message-ID: <20200515221255.GE94522@carbon.DHCP.thefacebook.com> References: <20200425024625.GA107755@carbon.lan> <20200427164638.GC114719@carbon.DHCP.thefacebook.com> <20200430171558.GA339283@carbon.dhcp.thefacebook.com> <20200504182922.GA20009@carbon.dhcp.thefacebook.com> <20200513005741.GA67541@carbon.dhcp.thefacebook.com> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-ClientProxiedBy: BY3PR10CA0015.namprd10.prod.outlook.com (2603:10b6:a03:255::20) To BYAPR15MB4136.namprd15.prod.outlook.com (2603:10b6:a03:96::24) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from carbon.DHCP.thefacebook.com (2620:10d:c090:400::5:aa2e) by BY3PR10CA0015.namprd10.prod.outlook.com (2603:10b6:a03:255::20) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3000.20 via Frontend Transport; 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X-MS-Exchange-AntiSpam-MessageData: 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 X-MS-Exchange-CrossTenant-Network-Message-Id: 7c8944d5-ff65-4ffc-5004-08d7f91d2000 X-MS-Exchange-CrossTenant-OriginalArrivalTime: 15 May 2020 22:12:58.4902 (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: nrjNg1cJwxWeDzzBkiAN2nMnBBXPpCKE1jovr0MK61cLXxr9mnuAApButz9oOT7C X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR15MB2405 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.216,18.0.676 definitions=2020-05-15_07:2020-05-15,2020-05-15 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 priorityscore=1501 impostorscore=0 cotscore=-2147483648 malwarescore=0 phishscore=0 spamscore=0 lowpriorityscore=0 suspectscore=1 adultscore=0 bulkscore=0 mlxscore=0 mlxlogscore=999 clxscore=1015 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2004280000 definitions=main-2005150187 X-FB-Internal: deliver 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 15, 2020 at 09:45:30PM +0000, Christoph Lameter wrote: > On Tue, 12 May 2020, Roman Gushchin wrote: > > > > Add it to the metadata at the end of the object. Like the debugging > > > information or the pointer for RCU freeing. > > > > Enabling debugging metadata currently disables the cache merging. > > I doubt that it's acceptable to sacrifice the cache merging in order > > to embed the memcg pointer? > > Well then keep the merging even if you have a memcg pointer. > > The disabling for debugging is only to simplify debugging. You dont have > to deal with multiple caches actually using the same storage structures. > > > Figuring out all these details will likely take several weeks, so the whole > > thing will be delayed for one-two major releases (in the best case). Given that > > the current implementation saves ~40% of slab memory, I think there is some value > > in delivering it as it is. So I wonder if the idea of embedding the pointer > > should be considered a blocker, or it can be implemented of top of the proposed > > code (given it's not a user-facing api or something like this)? > > Sorry no idea from my end here. Ok, then I'll continue working on the embedding the pointer as an enhancement *on top* of the current patchset. As I showed in my other e-mail, switching to a different way of obj_cgroup storage is fairly trivial and doesn't change much in the rest of the patchset. Please, let me know if you're not ok with it. Thanks!