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[209.85.220.65]) by mx.google.com with SMTPS id h76sor11952325ith.32.2019.04.11.18.33.32 for (Google Transport Security); Thu, 11 Apr 2019 18:33:43 -0700 (PDT) Received-SPF: pass (google.com: domain of laoar.shao@gmail.com designates 209.85.220.65 as permitted sender) client-ip=209.85.220.65; Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b="uFVBzBn/"; spf=pass (google.com: domain of laoar.shao@gmail.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=laoar.shao@gmail.com; dmarc=pass (p=NONE sp=QUARANTINE dis=NONE) header.from=gmail.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=afm2gQKQ9IeGQx2pSJdzpkAY9emExLqLGJxnADAziCM=; b=uFVBzBn/XKsdSbFAr75R43re28oYkar9/dySYhidvvklad41ZAe6tINRSBE012k4Vi 1Mo/faG0MOcHQdGY0KozwvZnsAp4IRqA9mUcwYc7cJ0z1BAi3hj5bN6x5yueg+8Bk0FF LHMzPWH4T4fC4j0wd5cHOAs937wk84PSrBp+qUgA9tscPdwWmTT0Yqfj6ro5pFnd8Gzs zNYDLNm4458mtYb6uKMxe8fXqKmw/sMYenDjpKkn9WZlJXJ7SLCNpQqpMnStN6xK94Gz KVBiEH5/VyD0C5ogMll20JGaiSiEjZNqfFVysaXTgWUVQVIaZYQEGPjJxK+yP0hRPqlh xq7A== X-Google-Smtp-Source: APXvYqyM4TgUZuTHtz73x16s4ARd2g2xo8LP0SurIYdjBfzQc+moaQUywpruP697lVgxAfiXB7x7RIy5xcbwXet0Bi8= X-Received: by 2002:a24:ba15:: with SMTP id p21mr9579383itf.66.1555032812298; Thu, 11 Apr 2019 18:33:32 -0700 (PDT) MIME-Version: 1.0 References: <1554983991-16769-1-git-send-email-laoar.shao@gmail.com> <20190411122659.GW10383@dhcp22.suse.cz> <20190411133300.GX10383@dhcp22.suse.cz> <20190411151039.GY10383@dhcp22.suse.cz> In-Reply-To: <20190411151039.GY10383@dhcp22.suse.cz> From: Yafang Shao Date: Fri, 12 Apr 2019 09:32:55 +0800 Message-ID: Subject: Re: [PATCH] mm/memcg: add allocstall to memory.stat To: Michal Hocko Cc: Johannes Weiner , Chris Down , Andrew Morton , Cgroups , Linux MM , shaoyafang@didiglobal.com Content-Type: text/plain; charset="UTF-8" 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 Thu, Apr 11, 2019 at 11:10 PM Michal Hocko wrote: > > On Thu 11-04-19 21:54:22, Yafang Shao wrote: > > On Thu, Apr 11, 2019 at 9:39 PM Michal Hocko wrote: > > > > > > On Thu 11-04-19 20:41:32, Yafang Shao wrote: > > > > On Thu, Apr 11, 2019 at 8:27 PM Michal Hocko wrote: > > > > > > > > > > On Thu 11-04-19 19:59:51, Yafang Shao wrote: > > > > > > The current item 'pgscan' is for pages in the memcg, > > > > > > which indicates how many pages owned by this memcg are scanned. > > > > > > While these pages may not scanned by the taskes in this memcg, even for > > > > > > PGSCAN_DIRECT. > > > > > > > > > > > > Sometimes we need an item to indicate whehter the tasks in this memcg > > > > > > under memory pressure or not. > > > > > > So this new item allocstall is added into memory.stat. > > > > > > > > > > We do have memcg events for that purpose and those can even tell whether > > > > > the pressure is a result of high or hard limit. Why is this not > > > > > sufficient? > > > > > > > > > > > > > The MEMCG_HIGH and MEMCG_LOW may not be tiggered by the tasks in this > > > > memcg neither. > > > > They all reflect the memory status of a memcg, rather than tasks > > > > activity in this memcg. > > > > > > I do not follow. Can you give me an example when does this matter? I > > > > For example, the tasks in this memcg may encounter direct page reclaim > > due to system memory pressure, > > meaning it is stalling in page alloc slow path. > > At the same time, maybe there's no memory pressure in this memcg, I > > mean, it could succussfully charge memcg. > > And that is exactly what those events aim for. They are measuring > _where_ the memory pressure comes from. > > Can you please try to explain what do you want to achieve again? To know the impact of this memory pressure. The current events can tell us the source of this pressure, but can't tell us the impact of this pressure. The tracepoints are always off until we meet some issue and then turn it on; while the event counter is more lightweight, and with it we can know which memcg is suffering this pressure. Thanks Yafang