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[209.85.220.41]) by mx.google.com with SMTPS id q7sor113687ywg.94.2019.05.23.11.49.52 for (Google Transport Security); Thu, 23 May 2019 11:49:53 -0700 (PDT) Received-SPF: pass (google.com: domain of shakeelb@google.com designates 209.85.220.41 as permitted sender) client-ip=209.85.220.41; Authentication-Results: mx.google.com; dkim=pass header.i=@google.com header.s=20161025 header.b="u0BN/6Ny"; spf=pass (google.com: domain of shakeelb@google.com designates 209.85.220.41 as permitted sender) smtp.mailfrom=shakeelb@google.com; dmarc=pass (p=REJECT sp=REJECT dis=NONE) header.from=google.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=q/4hzu5ZLVp3mgIPesJPmq/IWbfe4flwA2HG1sCD0TQ=; b=u0BN/6Ny8Z4+blOm22Z5UCSC8Wy5XnV4pzNa9RSEvcRmexqQPvcwNghBha2X4MQ36C 7dzsdV+f6ydrqcsngoZ6b81Z6BiBjBfDHoUWeZaLAK49agcruYHxVKfgwvl6vkbI7a2g qWF7FK3K5DeBcV4zvxpXp0o81by/At5dYBRjnk7yfQBXl0RTZNucfLEpe2dPkSFCumKX lM23S8zrXdpTm2qs3mlX+TjAUJg+SGmA3p+ePvgDlWxlg/5n+eJfvBZ/ka/EFGLzfvai bSt2zk6ItfPP82e9IfgqRiHMA9BW3IYp9vtRWaIl180exc8Z8hQL9gAUR3c4PwBkBOO2 q+Yw== X-Google-Smtp-Source: APXvYqzw3j/oSC5Q9iYfqvGAp+HoFdUfIIMs+Btzd/EKLDObZYBH8mQUpoL/qVeAVC9OPWePoER5CA68wIGZsaWSqM0= X-Received: by 2002:a81:5ec3:: with SMTP id s186mr47879009ywb.308.1558637392374; Thu, 23 May 2019 11:49:52 -0700 (PDT) MIME-Version: 1.0 References: <20190523174349.GA10939@cmpxchg.org> <20190523183713.GA14517@bombadil.infradead.org> In-Reply-To: <20190523183713.GA14517@bombadil.infradead.org> From: Shakeel Butt Date: Thu, 23 May 2019 11:49:41 -0700 Message-ID: Subject: Re: xarray breaks thrashing detection and cgroup isolation To: Matthew Wilcox Cc: Johannes Weiner , Andrew Morton , Linux MM , linux-fsdevel , LKML , Kernel Team 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, May 23, 2019 at 11:37 AM Matthew Wilcox wrote: > > On Thu, May 23, 2019 at 01:43:49PM -0400, Johannes Weiner wrote: > > I noticed that recent upstream kernels don't account the xarray nodes > > of the page cache to the allocating cgroup, like we used to do for the > > radix tree nodes. > > > > This results in broken isolation for cgrouped apps, allowing them to > > escape their containment and harm other cgroups and the system with an > > excessive build-up of nonresident information. > > > > It also breaks thrashing/refault detection because the page cache > > lives in a different domain than the xarray nodes, and so the shadow > > shrinker can reclaim nonresident information way too early when there > > isn't much cache in the root cgroup. > > > > I'm not quite sure how to fix this, since the xarray code doesn't seem > > to have per-tree gfp flags anymore like the radix tree did. We cannot > > add SLAB_ACCOUNT to the radix_tree_node_cachep slab cache. And the > > xarray api doesn't seem to really support gfp flags, either (xas_nomem > > does, but the optimistic internal allocations have fixed gfp flags). > > Would it be a problem to always add __GFP_ACCOUNT to the fixed flags? > I don't really understand cgroups. Does xarray cache allocated nodes, something like radix tree's: static DEFINE_PER_CPU(struct radix_tree_preload, radix_tree_preloads) = { 0, }; For the cached one, no __GFP_ACCOUNT flag. Also some users of xarray may not want __GFP_ACCOUNT. That's the reason we had __GFP_ACCOUNT for page cache instead of hard coding it in radix tree. Shakeel