From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from ozlabs.org (ozlabs.org [IPv6:2401:3900:2:1::2]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id CD98C1A0341 for ; Thu, 25 Feb 2016 15:12:30 +1100 (AEDT) Message-ID: <1456373550.30375.3.camel@ellerman.id.au> Subject: Re: Problems with swapping in v4.5-rc on POWER From: Michael Ellerman To: Hugh Dickins , "Aneesh Kumar K.V" Cc: linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org Date: Thu, 25 Feb 2016 15:12:30 +1100 In-Reply-To: References: Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Wed, 2016-02-24 at 18:10 -0800, Hugh Dickins via Linuxppc-dev wrote: > I've plagiarized the subject from Paulus's "Problems with THP" mail > last weekend; but my similar problems are on PowerMac G5 baremetal, > with 4kB pages, not capable of THP and no THP configured in. > > Under heavily swapping load, running kernel builds on tmpfs in limited > memory, I've been seeing random segfaults too, internal compiler errors > etc. Not easily reproduced: sometimes happens in minutes, sometimes > not for several hours. > > I tried and failed to construct a reproducer for you: my lack of a good > recipe has deterred me from reporting it, and seeing Paulus's mail on > THP gave me hope that the answer would come up in that thread; but no, > that was quickly resolved as a THP issue, since fixed. > > (Mine had appeared to be fixed in v4.5-rc4 anyway; but I guess I > just didn't try hard enough, it resurfaced on -rc5 immediately.) > > I've seen no sign of such problems on x86. And I saw no sign of such > problems on v4.4-rc8-mm1, when I included the fixes to the _PAGE_PTE > and _PAGE_SWP_SOFT_DIRTY swapoff issues we discussed back then (in > 33 hours of load, should be good enough; but did see such problems > a couple of times before including those fixes - I took them to be > a side-effect of the page flags issue, but now rather doubt that). > > The minutes or hours thing: I wonder if that indicates a missing > initialization somewhere: that can easily show up soon after booting, > but then the machine settles into a steady state of reusing the same > structures, now initialized; until much later something disturbs the > state and it has to allocate more. Sheer speculation, but I wonder. Thanks Hugh. I do run tests on G5, but obviously not rigorously enough. I kicked off a few kernel builds on mine and it survived, though once it hits swap it's almost unusably slow. I'll leave it running overnight and see if I hit anything. cheers From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-io0-f170.google.com (mail-io0-f170.google.com [209.85.223.170]) by kanga.kvack.org (Postfix) with ESMTP id C208F6B0005 for ; Wed, 24 Feb 2016 23:12:35 -0500 (EST) Received: by mail-io0-f170.google.com with SMTP id l127so75951588iof.3 for ; Wed, 24 Feb 2016 20:12:35 -0800 (PST) Received: from ozlabs.org (ozlabs.org. [103.22.144.67]) by mx.google.com with ESMTPS id g101si7558843ioi.116.2016.02.24.20.12.33 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 24 Feb 2016 20:12:33 -0800 (PST) Message-ID: <1456373550.30375.3.camel@ellerman.id.au> Subject: Re: Problems with swapping in v4.5-rc on POWER From: Michael Ellerman Date: Thu, 25 Feb 2016 15:12:30 +1100 In-Reply-To: References: Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Hugh Dickins , "Aneesh Kumar K.V" Cc: linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org On Wed, 2016-02-24 at 18:10 -0800, Hugh Dickins via Linuxppc-dev wrote: > I've plagiarized the subject from Paulus's "Problems with THP" mail > last weekend; but my similar problems are on PowerMac G5 baremetal, > with 4kB pages, not capable of THP and no THP configured in. > > Under heavily swapping load, running kernel builds on tmpfs in limited > memory, I've been seeing random segfaults too, internal compiler errors > etc. Not easily reproduced: sometimes happens in minutes, sometimes > not for several hours. > > I tried and failed to construct a reproducer for you: my lack of a good > recipe has deterred me from reporting it, and seeing Paulus's mail on > THP gave me hope that the answer would come up in that thread; but no, > that was quickly resolved as a THP issue, since fixed. > > (Mine had appeared to be fixed in v4.5-rc4 anyway; but I guess I > just didn't try hard enough, it resurfaced on -rc5 immediately.) > > I've seen no sign of such problems on x86. And I saw no sign of such > problems on v4.4-rc8-mm1, when I included the fixes to the _PAGE_PTE > and _PAGE_SWP_SOFT_DIRTY swapoff issues we discussed back then (in > 33 hours of load, should be good enough; but did see such problems > a couple of times before including those fixes - I took them to be > a side-effect of the page flags issue, but now rather doubt that). > > The minutes or hours thing: I wonder if that indicates a missing > initialization somewhere: that can easily show up soon after booting, > but then the machine settles into a steady state of reusing the same > structures, now initialized; until much later something disturbs the > state and it has to allocate more. Sheer speculation, but I wonder. Thanks Hugh. I do run tests on G5, but obviously not rigorously enough. I kicked off a few kernel builds on mine and it survived, though once it hits swap it's almost unusably slow. I'll leave it running overnight and see if I hit anything. cheers -- 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