From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pd0-f175.google.com (mail-pd0-f175.google.com [209.85.192.175]) by kanga.kvack.org (Postfix) with ESMTP id 789DA6B00DC for ; Thu, 24 Oct 2013 06:42:51 -0400 (EDT) Received: by mail-pd0-f175.google.com with SMTP id g10so2229828pdj.20 for ; Thu, 24 Oct 2013 03:42:51 -0700 (PDT) Received: from psmtp.com ([74.125.245.102]) by mx.google.com with SMTP id hb3si1565627pac.239.2013.10.24.03.42.49 for ; Thu, 24 Oct 2013 03:42:50 -0700 (PDT) Received: by mail-ie0-f178.google.com with SMTP id x13so3628441ief.9 for ; Thu, 24 Oct 2013 03:42:48 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <526844E6.1080307@codeaurora.org> References: <526844E6.1080307@codeaurora.org> Date: Thu, 24 Oct 2013 18:42:48 +0800 Message-ID: Subject: Re: zram/zsmalloc issues in very low memory conditions From: Weijie Yang Content-Type: text/plain; charset=ISO-8859-1 Sender: owner-linux-mm@kvack.org List-ID: To: Olav Haugan Cc: minchan@kernel.org, sjenning@linux.vnet.ibm.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, semenzato@google.com, bob.liu@oracle.com On Thu, Oct 24, 2013 at 5:51 AM, Olav Haugan wrote: > I am trying to use zram in very low memory conditions and I am having > some issues. zram is in the reclaim path. So if the system is very low > on memory the system is trying to reclaim pages by swapping out (in this > case to zram). However, since we are very low on memory zram fails to > get a page from zsmalloc and thus zram fails to store the page. We get > into a cycle where the system is low on memory so it tries to swap out > to get more memory but swap out fails because there is not enough memory > in the system! The major problem I am seeing is that there does not seem > to be a way for zram to tell the upper layers to stop swapping out > because the swap device is essentially "full" (since there is no more > memory available for zram pages). Has anyone thought about this issue > already and have ideas how to solve this or am I missing something and I > should not be seeing this issue? I agree with Luigi and Bob. zram's size is based on how many free memory you expect to use for zram. In my test, the compression ratio is about 1:4, of course the working sets may be different with yours. Further more, may be you can modify vm_swap_full() to let kernel free swap_entry aggressively. > I am also seeing a couple other issues that I was wondering whether > folks have already thought about: > > 1) The size of a swap device is statically computed when the swap device > is turned on (nr_swap_pages). The size of zram swap device is dynamic > since we are compressing the pages and thus the swap subsystem thinks > that the zram swap device is full when it is not really full. Any > plans/thoughts about the possibility of being able to update the size > and/or the # of available pages in a swap device on the fly? > > 2) zsmalloc fails when the page allocated is at physical address 0 (pfn > = 0) since the handle returned from zsmalloc is encoded as (, > ) and thus the resulting handle will be 0 (since obj_idx starts > at 0). zs_malloc returns the handle but does not distinguish between a > valid handle of 0 and a failure to allocate. A possible solution to this > would be to start the obj_idx at 1. Is this feasible? > > Thanks, > > Olav Haugan > > -- > The Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, > hosted by The Linux Foundation > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org