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Wed, 13 Nov 2024 15:01:51 +0000 Received: from BYAPR10MB3366.namprd10.prod.outlook.com ([fe80::baf2:dff1:d471:1c9]) by BYAPR10MB3366.namprd10.prod.outlook.com ([fe80::baf2:dff1:d471:1c9%7]) with mapi id 15.20.8137.027; Wed, 13 Nov 2024 15:01:51 +0000 Date: Wed, 13 Nov 2024 15:01:48 +0000 From: Lorenzo Stoakes To: Suren Baghdasaryan Cc: akpm@linux-foundation.org, willy@infradead.org, liam.howlett@oracle.com, mhocko@suse.com, vbabka@suse.cz, hannes@cmpxchg.org, mjguzik@gmail.com, oliver.sang@intel.com, mgorman@techsingularity.net, david@redhat.com, peterx@redhat.com, oleg@redhat.com, dave@stgolabs.net, paulmck@kernel.org, brauner@kernel.org, dhowells@redhat.com, hdanton@sina.com, hughd@google.com, minchan@google.com, jannh@google.com, shakeel.butt@linux.dev, souravpanda@google.com, pasha.tatashin@soleen.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@android.com Subject: Re: [PATCH v2 2/5] mm: move per-vma lock into vm_area_struct Message-ID: <5d34da83-92eb-4666-816c-73a0e831aa89@lucifer.local> References: <20241112194635.444146-1-surenb@google.com> <20241112194635.444146-3-surenb@google.com> <637370b8-3e3e-4457-81d6-5913a3ff1d4e@lucifer.local> Content-Type: text/plain; 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Recent investigation [2] revealed that the > > regressions is limited to a rather old Broadwell microarchitecture and > > even there it can be mitigated by disabling adjacent cacheline > > prefetching, see [3]. > > I don't see a motivating reason as to why we want to do this? We increase > memory usage here which is not good, but later lock optimisation mitigates > it, but why wouldn't we just do the lock optimisations and use less memory > overall? I worded this badly. To clarify: I don't see a motivating reason _in the commit message_ as to why we want to do this. I am certain there are, in fact Mateusz and Vlastimil have provided them. So my review is - let's just put these there :)