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Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1pP718-00H1HJ-Qd; Mon, 06 Feb 2023 19:19:06 +0000 Date: Mon, 6 Feb 2023 19:19:06 +0000 From: Matthew Wilcox To: Marcelo Tosatti Cc: Christoph Lameter , Aaron Tomlin , Frederic Weisbecker , Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH 3/5] mm/vmstat: use cmpxchg loop in cpu_vm_stats_fold Message-ID: References: <20230201195013.881721887@redhat.com> <20230201195104.460373427@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230201195104.460373427@redhat.com> X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 5D9A4C0015 X-Stat-Signature: apem9si5cufng8qdrp66whb6nxbcdcue X-HE-Tag: 1675711159-898466 X-HE-Meta: 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 BqPlDD+Y UvI5DXGBsEc0RxgIz8GVmPlbiY1OOeeMNogxtZaGNoi3rS7f1P9Zt8IpThrLC8jySqf+Xi5w9ge0ei0zTM97YNKFpjanqvasd4e48BVJOQmmKkwtSK+LfcRvOviyLkcrQw/tIZMWugz6P2Bw6cKWQf3FE2FnT9VtyXDsA X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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));