From mboxrd@z Thu Jan  1 00:00:00 1970
From: Kent Overstreet <kent.overstreet@linux.dev>
Subject: Re: [PATCH 00/40] Memory allocation profiling
Date: Wed, 3 May 2023 23:33:08 -0400
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To: Tejun Heo <tj@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>, Johannes Weiner <hannes@cmpxchg.org>, Michal Hocko <mhocko@suse.com>, akpm@linux-foundation.org, vbabka@suse.cz, roman.gushchin@linux.dev, mgorman@suse.de, dave@stgolabs.net, willy@infradead.org, liam.howlett@oracle.com, corbet@lwn.net, void@manifault.com, peterz@infradead.org, juri.lelli@redhat.com, ldufour@linux.ibm.com, catalin.marinas@arm.com, will@kernel.org, arnd@arndb.de, tglx@linutronix.de, mingo@redhat.com, dave.hansen@linux.intel.com, x86@kernel.org, peterx@redhat.com, david@redhat.com, axboe@kernel.dk, mcgrof@kernel.org, masahiroy@kernel.org, nathan@kernel.org, dennis@kernel.org, muchun.song@linux.dev, rppt@kernel.org, paulmck@kernel.org, pasha.tatashin@soleen.com, yosryahmed@google.com, yuzhao@google.com, dhowells@redhat.com

On Wed, May 03, 2023 at 04:25:30PM -1000, Tejun Heo wrote:
> I see. I'm a bit skeptical about the performance angle given that the hot
> path can be probably made really cheap even with lookups. In most cases,
> it's just gonna be an extra pointer deref and a few more arithmetics. That
> can show up in microbenchmarks but it's not gonna be much. The benefit of
> going that route would be the tracking thing being mostly self contained.

The only way to do it with a single additional pointer deref would be
with a completely statically sized hash table without chaining - it'd
have to be open addressing.

More realistically you're looking at ~3 dependent loads.