linux-kernel - Re: [RFC PATCH v8 1/9] Restartable sequences system call

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Message-ID: <CA+55aFwo7LJ95fKBAhzcu6kCLd5=73n9M6QOq-mMaYO-d5dCVw@mail.gmail.com>
Date:   Fri, 19 Aug 2016 14:32:13 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Paul McKenney <paulmck@...ux.vnet.ibm.com>
Cc:     Andi Kleen <andi@...stfloor.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Boqun Feng <boqun.feng@...il.com>,
        Andy Lutomirski <luto@...capital.net>,
        Dave Watson <davejwatson@...com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        Paul Turner <pjt@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Russell King <linux@....linux.org.uk>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, Andrew Hunter <ahh@...gle.com>,
        Chris Lameter <cl@...ux.com>, Ben Maurer <bmaurer@...com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Josh Triplett <josh@...htriplett.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Michael Kerrisk <mtk.manpages@...il.com>
Subject: Re: [RFC PATCH v8 1/9] Restartable sequences system call

On Fri, Aug 19, 2016 at 2:19 PM, Paul E. McKenney
<paulmck@...ux.vnet.ibm.com> wrote:
> On Fri, Aug 19, 2016 at 01:56:11PM -0700, Andi Kleen wrote:
>>
>> malloc is the primary target I believe. Saves lots of memory to keep
>> caches per CPU rather than per thread.
>
> Agreed, a competent default malloc() in glibc would be a very nice change
> from the current state.

I agree that malloc can be a very good target for something like this,
but it is also something that is quite complicated. A general-purpose
allocator that could be used by glibc and has not just the performance
but the debug stuff etc that people inevitably want is a big project.
And then the people who have special needs end up writing their own
allocators anyway, just because they care about certain layout and
access patterns...

Put another way: I'd really like to see some real numbers and use,
rather than "this can be used for.."

             Linus