From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 29732C433EF for ; Thu, 28 Apr 2022 14:06:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1348041AbiD1OJO (ORCPT ); Thu, 28 Apr 2022 10:09:14 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44324 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1348334AbiD1OJG (ORCPT ); Thu, 28 Apr 2022 10:09:06 -0400 Received: from mail-qk1-x736.google.com (mail-qk1-x736.google.com [IPv6:2607:f8b0:4864:20::736]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 17220201BB for ; Thu, 28 Apr 2022 07:05:51 -0700 (PDT) Received: by mail-qk1-x736.google.com with SMTP id x77so2856411qkb.3 for ; Thu, 28 Apr 2022 07:05:51 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=cmpxchg-org.20210112.gappssmtp.com; s=20210112; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=EWNhQ6rVh6eXAW1cPKtOkkQDFiBPnV60f02tyxwR5Yc=; b=nibOfdXs0pW9RsNjEJkkttSRKnNqlNrv3VGuEoDx+NjanzQTMrPiHJBi6jLuBYlEBX NcO/5bG7QV10FdfyjroVW7zjvHmRCL6rESoVffMrL0roquyhR0RiqvnKOugcVXNzxQUv k+KjGFlWbI1y1+uZBSyBAhb5DLIo4mcmwiJJWFRu2M4LMUruthwmPcQm1TZjTnVUbevG iUldqaSPXn3+1z5uyqObupucLM6SHgKfNXHInYKV6a7ZZmUdMxKwRsdHyfT2sAGbHgZF D760Af4oY/VmKyobDe06ICDwWWOcI7CqP4m48CjvnuCsv6BaaaKe/enYr7XQgP56Ehbf 7YeA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=EWNhQ6rVh6eXAW1cPKtOkkQDFiBPnV60f02tyxwR5Yc=; b=1/QjtJEE+aoBwXJXtN2AO8m6d2hzdh/YuP34R1YzT3JIHUkek2lquWBoHW/V9mW/iX KfjEZLeCyNHp/4mNKUE1kogr1QUnOndHIQmm918UR7zsxd2YmmKa5uYd/Hx/gYoprC5r DL96Praimq7gCoSnPElecebHKRsjc/J2iyNCdBUAanW99qWyolMBwllpMQwYYT1honXj UTsvqTbLcOHXgr6aUx9qlnbBdoTJHWWsAt2qMy7MP/k6wjP+zmehDQaXI2/tc5ZWBMMV kvABTL+8YfjVCfGpBN3OURp5nVOH77qSiH6M4Wuxbt6lQpRJx0DNbzMnh8wDS1Tb3z9l yUDA== X-Gm-Message-State: AOAM532aHzFTCvhQwQ2IJfxySh9LTjnNN0Tw5oJhN2aJvJvmk87JaNIn riovqathuHq7X8z2Nu4IPNq69g== X-Google-Smtp-Source: ABdhPJzYZvJDZXce9yZA3Kg+yP+dJzbTC8DyT0C7ZcSkd7lrwBMQGBGM5G6sPvmBbM9uR/KzYMco7Q== X-Received: by 2002:a05:620a:3195:b0:69f:ac68:4cae with SMTP id bi21-20020a05620a319500b0069fac684caemr1107547qkb.292.1651154750168; Thu, 28 Apr 2022 07:05:50 -0700 (PDT) Received: from localhost ([2620:10d:c091:480::1:d588]) by smtp.gmail.com with ESMTPSA id w4-20020a05620a0e8400b0067b1bcd081csm13278qkm.66.2022.04.28.07.05.49 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 28 Apr 2022 07:05:49 -0700 (PDT) Date: Thu, 28 Apr 2022 10:05:13 -0400 From: Johannes Weiner To: Minchan Kim Cc: Andrew Morton , Michal Hocko , Roman Gushchin , Shakeel Butt , Seth Jennings , Dan Streetman , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@fb.com Subject: Re: [PATCH 4/5] mm: zswap: add basic meminfo and vmstat coverage Message-ID: References: <20220427160016.144237-1-hannes@cmpxchg.org> <20220427160016.144237-5-hannes@cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Apr 27, 2022 at 03:12:17PM -0700, Minchan Kim wrote: > On Wed, Apr 27, 2022 at 05:36:26PM -0400, Johannes Weiner wrote: > > On Wed, Apr 27, 2022 at 05:20:31PM -0400, Johannes Weiner wrote: > > > On Wed, Apr 27, 2022 at 01:29:34PM -0700, Minchan Kim wrote: > > > > Hi Johannes, > > > > > > > > On Wed, Apr 27, 2022 at 12:00:15PM -0400, Johannes Weiner wrote: > > > > > Currently it requires poking at debugfs to figure out the size and > > > > > population of the zswap cache on a host. There are no counters for > > > > > reads and writes against the cache. As a result, it's difficult to > > > > > understand zswap behavior on production systems. > > > > > > > > > > Print zswap memory consumption and how many pages are zswapped out in > > > > > /proc/meminfo. Count zswapouts and zswapins in /proc/vmstat. > > > > > > > > > > Signed-off-by: Johannes Weiner > > > > > --- > > > > > fs/proc/meminfo.c | 7 +++++++ > > > > > include/linux/swap.h | 5 +++++ > > > > > include/linux/vm_event_item.h | 4 ++++ > > > > > mm/vmstat.c | 4 ++++ > > > > > mm/zswap.c | 13 ++++++------- > > > > > 5 files changed, 26 insertions(+), 7 deletions(-) > > > > > > > > > > diff --git a/fs/proc/meminfo.c b/fs/proc/meminfo.c > > > > > index 6fa761c9cc78..6e89f0e2fd20 100644 > > > > > --- a/fs/proc/meminfo.c > > > > > +++ b/fs/proc/meminfo.c > > > > > @@ -86,6 +86,13 @@ static int meminfo_proc_show(struct seq_file *m, void *v) > > > > > > > > > > show_val_kb(m, "SwapTotal: ", i.totalswap); > > > > > show_val_kb(m, "SwapFree: ", i.freeswap); > > > > > +#ifdef CONFIG_ZSWAP > > > > > + seq_printf(m, "Zswap: %8lu kB\n", > > > > > + (unsigned long)(zswap_pool_total_size >> 10)); > > > > > + seq_printf(m, "Zswapped: %8lu kB\n", > > > > > + (unsigned long)atomic_read(&zswap_stored_pages) << > > > > > + (PAGE_SHIFT - 10)); > > > > > +#endif > > > > > > > > I agree it would be very handy to have the memory consumption in meminfo > > > > > > > > https://lore.kernel.org/all/YYwZXrL3Fu8%2FvLZw@google.com/ > > > > > > > > If we really go this Zswap only metric instead of general term > > > > "Compressed", I'd like to post maybe "Zram:" with same reason > > > > in this patchset. Do you think that's better idea instead of > > > > introducing general term like "Compressed:" or something else? > > > > > > I'm fine with changing it to Compressed. If somebody cares about a > > > more detailed breakdown, we can add Zswap, Zram subsets as needed. > > > > It does raise the question what to do about cgroup, though. Should the > > control files (memory.zswap.current & memory.zswap.max) apply to zram > > in the future? If so, we should rename them, too. > > > > I'm not too familiar with zram, maybe you can provide some > > background. AFAIU, Google uses zram quite widely; all the more > > confusing why there is no container support for it yet. > > My usecase with zram is Android which doesn't use memcg. Ok. After more thought, my take is that in the future it could make sense to track zram pages in a cgroup's memory.current. But it should NOT be included in the dedicated memory.zswap.* files. Zswap is an in-kernel writeback cache, and those files allow userspace to tune writeback thresholds depending on the composition of the workload's workingset. This doesn't translate to zram: the wb facility that it has is triggered by hand, based on criteria such as idle pages and compression rate. It's not based on size. From a cgroup POV, it's a memory consumer that should be subject to memory.max, nothing more. This distinction applies to meminfo as well, though. While I think it makes sense to have a combined "Compressed" counter for zram and zswap, it's still important to understand zswap behavior on its own to tune the system-wide writeback threshold in max_pool_percent. (And again, while zram can also be limited, it's not a writeback threshold, it's just a red line for returning -ENOMEM). So I'm going to keep the Zswap and Zswapped items and retract the delta patch for renaming it to Compressed. But I'd ack a patch that adds a combined "Compressed" counter for zram + zswap if you send it, Minchan.