From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from ozlabs.org (ozlabs.org [103.22.144.67]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id BCBD11A07D4 for ; Sat, 20 Feb 2016 16:54:23 +1100 (AEDT) Date: Sat, 20 Feb 2016 16:54:19 +1100 From: Paul Mackerras To: linuxppc-dev@lists.ozlabs.org Cc: "Aneesh Kumar K.V" , linux-mm@kvack.org Subject: Re: Problems with THP in v4.5-rc4 on POWER Message-ID: <20160220055419.GB16191@fergus.ozlabs.ibm.com> References: <20160220013942.GA16191@fergus.ozlabs.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <20160220013942.GA16191@fergus.ozlabs.ibm.com> List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Sat, Feb 20, 2016 at 12:39:42PM +1100, Paul Mackerras wrote: > It seems there's something wrong with our transparent hugepage > implementation on POWER server processors as of v4.5-rc4. I have seen > the email thread on "[BUG] random kernel crashes after THP rework on > s390 (maybe also on PowerPC and ARM)", but this doesn't seem exactly > the same as that (though it may of course be related). > > I have been testing v4.5-rc4 with Aneesh's patch "powerpc/mm/hash: > Clear the invalid slot information correctly" on top, on a KVM guest > with 160 vcpus (threads=8) and 32GB of memory backed by 16MB large > pages, running on a POWER8 machine running a 4.4.1 host kernel (20 > cores * 8 threads, 128GB of RAM). The guest kernel is compiled with > THP enabled and set to "always" (i.e. not "madvise"). > > On this setup, when doing something like a large kernel compile, I see > random segfaults happening (in gcc, cc1, sh, etc.). I also see bursts > of messages like this on the host console: > > [50957.570859] Harmless Hypervisor Maintenance interrupt [Recovered] > [50957.570864] Error detail: Processor Recovery done > [50957.570869] HMER: 2040000000000000 When I use a merge of v4.5-rc4 with the fixes branch from the powerpc tree, I don't see these messages any more, presumably due to "powerpc/mm: Fix Multi hit ERAT cause by recent THP update". With my patch, I still see that it is finding HPTEs to invalidate, but without my patch, even though it is presumably leaving HPTEs around, I don't see any errors (such as random segfaults) occurring. Paul.