From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 79A0220E6E2; Thu, 8 Jan 2026 19:10:28 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767899428; cv=none; b=YnvwASIoUT5qQ368JQp+nERXlcuav2ObPWI06KlH3/w+bTQeI81IXo7V/MtrNx6JqUnC86lOeA2bTtitFEYuesSsn4lOYpn+Dkb7QlJy2UjFhQbjGMM78QPnoDjuibv2Td6+cktxmYDeturwt9uSsckrYvmdlALOJIh3lvjklR8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767899428; c=relaxed/simple; bh=VNrN8JUZQcrq/pnCYgjUgfyW0bmZkPgoeILN/bAbbMI=; h=Date:From:To:Cc:Subject:Message-Id:In-Reply-To:References: Mime-Version:Content-Type; b=DJV787+G3fvSxDUIj/pT4hVYs8aa9V+qoaLAI1SDA2WlmGFf9E/MGUh9HEPMFytDYlZBKOUhrYjuRAF3akya1wNQ/1VF+gdH2JGwmfemVy6Krs0mi7DuoQUYHjWveeFPfYbXgRdrhBdv2ygllJ4unJd73R0KdqqQzuLJHqGgPzA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=g3EeLTXU; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="g3EeLTXU" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D2662C116C6; Thu, 8 Jan 2026 19:10:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1767899428; bh=VNrN8JUZQcrq/pnCYgjUgfyW0bmZkPgoeILN/bAbbMI=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=g3EeLTXUeU3eKRuS7y4uPO7sanUqMNZ5VF1Qp663J3H3gUDLjN9dx6+io8FYXgDPU 8NXIBIRdOMKfJwd4YfT+RwvyMLCa2/ZuyAwt01EYIQ5PjiSR4ZN3K+57VDA1VyHQPf oe6G5dewC7dXXQEN8iLnyIst4LRTtL+WbdH7HiJA= Date: Thu, 8 Jan 2026 11:10:27 -0800 From: Andrew Morton To: Jianyue Wu Cc: jianyuew@nvidia.com, hannes@cmpxchg.org, mhocko@kernel.org, roman.gushchin@linux.dev, shakeel.butt@linux.dev, muchun.song@linux.dev, linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm: optimize stat output for 11% sys time reduce Message-Id: <20260108111027.172f19a9a86667e8e0142042@linux-foundation.org> In-Reply-To: <20260108093741.212333-1-jianyuew@nvidia.com> References: <20260108093741.212333-1-jianyuew@nvidia.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Thu, 8 Jan 2026 17:37:29 +0800 Jianyue Wu wrote: > From: Jianyue Wu > > Replace seq_printf/seq_buf_printf with lightweight helpers to avoid > printf parsing in memcg stats output. > > Key changes: > - Add memcg_seq_put_name_val() for seq_file "name value\n" formatting > - Add memcg_seq_buf_put_name_val() for seq_buf "name value\n" formatting > - Update __memory_events_show(), swap_events_show(), > memory_stat_format(), memory_numa_stat_show(), and related helpers > > Performance: > - 1M reads of memory.stat+memory.numa_stat > - Before: real 0m9.663s, user 0m4.840s, sys 0m4.823s > - After: real 0m9.051s, user 0m4.775s, sys 0m4.275s (~11.4% sys drop) > > Tests: > - Script: > for ((i=1; i<=1000000; i++)); do > : > /dev/null < /sys/fs/cgroup/memory.stat > : > /dev/null < /sys/fs/cgroup/memory.numa_stat > done > I suspect there are workloads which read these files frequently. I'd be interested in learning "how frequently". Perhaps ascii-through-sysfs simply isn't an appropriate API for this data? > @@ -1795,25 +1795,33 @@ static int memcg_numa_stat_show(struct seq_file *m, void *v) > mem_cgroup_flush_stats(memcg); > > for (stat = stats; stat < stats + ARRAY_SIZE(stats); stat++) { > - seq_printf(m, "%s=%lu", stat->name, > - mem_cgroup_nr_lru_pages(memcg, stat->lru_mask, > - false)); > - for_each_node_state(nid, N_MEMORY) > - seq_printf(m, " N%d=%lu", nid, > - mem_cgroup_node_nr_lru_pages(memcg, nid, > - stat->lru_mask, false)); > + seq_puts(m, stat->name); > + seq_put_decimal_ull(m, "=", > + (u64)mem_cgroup_nr_lru_pages(memcg, stat->lru_mask, > + false)); > + for_each_node_state(nid, N_MEMORY) { > + seq_put_decimal_ull(m, " N", nid); > + seq_put_decimal_ull(m, "=", > + (u64)mem_cgroup_node_nr_lru_pages(memcg, nid, > + stat->lru_mask, false)); The indenting went wrong here. The patch does do a lot of ugly tricks to constrain the number of columns used. Perhaps introduce some new local variables to clean this up?