linux-kernel - Re: [PATCH v3 31/35] lib: add memory allocations report in show

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <a3ha7fchkeugpthmatm5lw7chg6zxkapyimn3qio3pkoipg4tc@3j6xfdfoustw>
Date: Thu, 15 Feb 2024 19:50:24 -0500
From: Kent Overstreet <kent.overstreet@...ux.dev>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: Vlastimil Babka <vbabka@...e.cz>, 
	Suren Baghdasaryan <surenb@...gle.com>, Michal Hocko <mhocko@...e.com>, akpm@...ux-foundation.org, 
	hannes@...xchg.org, roman.gushchin@...ux.dev, mgorman@...e.de, dave@...olabs.net, 
	willy@...radead.org, liam.howlett@...cle.com, corbet@....net, void@...ifault.com, 
	peterz@...radead.org, juri.lelli@...hat.com, catalin.marinas@....com, will@...nel.org, 
	arnd@...db.de, tglx@...utronix.de, mingo@...hat.com, 
	dave.hansen@...ux.intel.com, x86@...nel.org, peterx@...hat.com, david@...hat.com, 
	axboe@...nel.dk, mcgrof@...nel.org, masahiroy@...nel.org, nathan@...nel.org, 
	dennis@...nel.org, tj@...nel.org, muchun.song@...ux.dev, rppt@...nel.org, 
	paulmck@...nel.org, pasha.tatashin@...een.com, yosryahmed@...gle.com, 
	yuzhao@...gle.com, dhowells@...hat.com, hughd@...gle.com, andreyknvl@...il.com, 
	keescook@...omium.org, ndesaulniers@...gle.com, vvvvvv@...gle.com, 
	gregkh@...uxfoundation.org, ebiggers@...gle.com, ytcoode@...il.com, 
	vincent.guittot@...aro.org, dietmar.eggemann@....com, bsegall@...gle.com, bristot@...hat.com, 
	vschneid@...hat.com, cl@...ux.com, penberg@...nel.org, iamjoonsoo.kim@....com, 
	42.hyeyoo@...il.com, glider@...gle.com, elver@...gle.com, dvyukov@...gle.com, 
	shakeelb@...gle.com, songmuchun@...edance.com, jbaron@...mai.com, rientjes@...gle.com, 
	minchan@...gle.com, kaleshsingh@...gle.com, kernel-team@...roid.com, 
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, iommu@...ts.linux.dev, 
	linux-arch@...r.kernel.org, linux-fsdevel@...r.kernel.org, linux-mm@...ck.org, 
	linux-modules@...r.kernel.org, kasan-dev@...glegroups.com, cgroups@...r.kernel.org
Subject: Re: [PATCH v3 31/35] lib: add memory allocations report in show_mem()

On Thu, Feb 15, 2024 at 07:39:15PM -0500, Steven Rostedt wrote:
> On Thu, 15 Feb 2024 19:32:38 -0500
> Kent Overstreet <kent.overstreet@...ux.dev> wrote:
> 
> > > But where are the benchmarks that are not micro-benchmarks. How much
> > > overhead does this cause to those? Is it in the noise, or is it noticeable?  
> > 
> > Microbenchmarks are how we magnify the effect of a change like this to
> > the most we'll ever see. Barring cache effects, it'll be in the noise.
> > 
> > Cache effects are a concern here because we're now touching task_struct
> > in the allocation fast path; that is where the
> > "compiled-in-but-turned-off" overhead comes from, because we can't add
> > static keys for that code without doubling the amount of icache
> > footprint, and I don't think that would be a great tradeoff.
> > 
> > So: if your code has fastpath allocations where the hot part of
> > task_struct isn't in cache, then this will be noticeable overhead to
> > you, otherwise it won't be.
> 
> All nice, but where are the benchmarks? This looks like it will have an
> affect on cache and you can talk all you want about how it will not be an
> issue, but without real world benchmarks, it's meaningless. Numbers talk.

Steve, you're being demanding. We provided sufficient benchmarks to show
the overhead is low enough for production, and then I gave you a
detailed breakdown of where our overhead is and where it'll show up. I
think that's reasonable.