From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Hurley Date: Tue, 04 Nov 2014 03:38:48 +0000 Subject: Re: CMA: test_pages_isolated failures in alloc_contig_range Message-Id: <54584A48.9000409@hurleysoftware.com> List-Id: References: <2457604.k03RC2Mv4q@avalon> <544F9EAA.5010404@hurleysoftware.com> In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Michal Nazarewicz , Laurent Pinchart , linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, linux-sh@vger.kernel.org, Bartlomiej Zolnierkiewicz , Minchan Kim , Andrew Morton On 10/28/2014 12:57 PM, Michal Nazarewicz wrote: >> On 10/28/2014 08:38 AM, Michal Nazarewicz wrote: >>> Like Laura wrote, the message is not (should not be) a problem in >>> itself: >> >> [...] >> >>> So as you can see cma_alloc will try another part of the cma region if >>> test_pages_isolated fails. >>> >>> Obviously, if CMA region is fragmented or there's enough space for only >>> one allocation of required size isolation failures will cause allocation >>> failures, so it's best to avoid them, but they are not always avoidable. >>> >>> To debug you would probably want to add more debug information about the >>> page (i.e. data from struct page) that failed isolation after the >>> pr_warn in alloc_contig_range. > > On Tue, Oct 28 2014, Peter Hurley wrote: >> If the message does not indicate an actual problem, then its printk level is >> too high. These messages have been reported when using 3.16+ distro kernels. > > I think it could be argued both ways. The condition is not an error, > since in many cases cma_alloc will be able to continue, but it *is* an > undesired state. As such it's not an error but feels to me a bit more > then just information, hence a warning. I don't care either way, though. This "undesired state" is trivially reproducible on 3.16.y on the x86 arch; a smattering of these will show up just building a distro kernel.