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[209.85.220.65]) by mx.google.com with SMTPS id q25sor29358901pgv.12.2019.08.04.21.14.47 for (Google Transport Security); Sun, 04 Aug 2019 21:14:47 -0700 (PDT) Received-SPF: pass (google.com: domain of minchan.kim@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=lUaKgKHU; spf=pass (google.com: domain of minchan.kim@gmail.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=minchan.kim@gmail.com; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=kernel.org DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=sender:date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=mva09u+yn1RWE+TO1luNzBDnrlH/Q/3QfIfoFJtdBKs=; b=lUaKgKHU3tYV6FVsndghO1nh62VmLyjBz+gnRDFzMtyQSKeK4kyNlKt7pfyVZI5dP0 lCmU53u7ZoMWT0GjNCzqnOSqZsjasDVwlPCqu3E04EBsomGuC5AAi2qOnGX+T6kdDxni dV6o/haUzLnNpKhvlZ15NuuJvVzUEFuORq2wb6M+ExKwYLtMUDhXsmnZ6PSmWyr8PWxE V0kct3Svkq8vUoVZOO289g/Yw0Wqon93UAVktJZ1iuJxKV0PoU8euDaXateelJ7JSx9o f40OBUyRw88R3NWa2O8csPHoyge5AVZZPF8py8aCAYxVK8+Dltiuo2QpqUbwAnXmRmta HM1g== X-Google-Smtp-Source: APXvYqxu85q5rU7e/DgfZCTuChdmrDTsIJLsBcmb1yRybucaAu5vmnJlY6V1Pxkezx8ce2esQ0uBSg== X-Received: by 2002:a63:7e1d:: with SMTP id z29mr134680099pgc.346.1564978486557; Sun, 04 Aug 2019 21:14:46 -0700 (PDT) Received: from google.com ([2401:fa00:d:0:98f1:8b3d:1f37:3e8]) by smtp.gmail.com with ESMTPSA id j1sm115888081pgl.12.2019.08.04.21.14.43 (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Sun, 04 Aug 2019 21:14:44 -0700 (PDT) Date: Mon, 5 Aug 2019 13:14:40 +0900 From: Minchan Kim To: Henry Burns Cc: Nitin Gupta , Sergey Senozhatsky , Shakeel Butt , Jonathan Adams , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/2] mm/zsmalloc.c: Migration can leave pages in ZS_EMPTY indefinitely Message-ID: <20190805041440.GA178551@google.com> References: <20190802015332.229322-1-henryburns@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190802015332.229322-1-henryburns@google.com> User-Agent: Mutt/1.10.1 (2018-07-13) 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, Aug 01, 2019 at 06:53:31PM -0700, Henry Burns wrote: > In zs_page_migrate() we call putback_zspage() after we have finished > migrating all pages in this zspage. However, the return value is ignored. > If a zs_free() races in between zs_page_isolate() and zs_page_migrate(), > freeing the last object in the zspage, putback_zspage() will leave the page > in ZS_EMPTY for potentially an unbounded amount of time. Nice catch. > > To fix this, we need to do the same thing as zs_page_putback() does: > schedule free_work to occur. To avoid duplicated code, move the > sequence to a new putback_zspage_deferred() function which both > zs_page_migrate() and zs_page_putback() call. > > Signed-off-by: Henry Burns Cc: [4.8+] Acked-by: Minchan Kim Below a just trivial: > --- > mm/zsmalloc.c | 30 ++++++++++++++++++++---------- > 1 file changed, 20 insertions(+), 10 deletions(-) > > diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c > index 1cda3fe0c2d9..efa660a87787 100644 > --- a/mm/zsmalloc.c > +++ b/mm/zsmalloc.c > @@ -1901,6 +1901,22 @@ static void dec_zspage_isolation(struct zspage *zspage) > zspage->isolated--; > } > > +static void putback_zspage_deferred(struct zs_pool *pool, > + struct size_class *class, > + struct zspage *zspage) > +{ > + enum fullness_group fg; > + > + fg = putback_zspage(class, zspage); > + /* > + * Due to page_lock, we cannot free zspage immediately > + * so let's defer. > + */ Could you move this comment function's description since it becomes a function? Thanks.