linux-kernel - Re: [PATCH 3/5] mm/vmstat: use cmpxchg loop in cpu_vm_stats

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] [day] [month] [year] [list]

Message-ID: <Y+FSqkDYfhKuBZIe@casper.infradead.org>
Date:   Mon, 6 Feb 2023 19:19:06 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Marcelo Tosatti <mtosatti@...hat.com>
Cc:     Christoph Lameter <cl@...ux.com>,
        Aaron Tomlin <atomlin@...mlin.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 3/5] mm/vmstat: use cmpxchg loop in cpu_vm_stats_fold

On Wed, Feb 01, 2023 at 04:50:16PM -0300, Marcelo Tosatti wrote:
> In preparation to switch vmstat shepherd to flush
> per-CPU counters remotely, use a cmpxchg loop 
> instead of a pair of read/write instructions.

FYI, try_cmpxchg() is preferred to plain cmpxchg() these days.
Apparently it generates better code on x86.

> -				v = pzstats->vm_stat_diff[i];
> -				pzstats->vm_stat_diff[i] = 0;
> +				do {
> +					v = pzstats->vm_stat_diff[i];
> +				} while (cmpxchg(&pzstats->vm_stat_diff[i], v, 0) != v);

I think this would be:

				do {
					v = pzstats->vm_stat_diff[i];
				} while (!try_cmpxchg(&pzstats->vm_stat_diff[i], v, 0));