From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Cyrus-Session-Id: sloti22d1t05-2753128-1517970194-2-12644981320582292058 X-Sieve: CMU Sieve 3.0 X-Spam-known-sender: no X-Spam-score: 0.0 X-Spam-hits: BAYES_00 -1.9, HEADER_FROM_DIFFERENT_DOMAINS 0.001, ME_NOAUTH 0.01, RCVD_IN_DNSWL_HI -5, T_RP_MATCHES_RCVD -0.01, LANGUAGES en, BAYES_USED global, SA_VERSION 3.4.0 X-Spam-source: IP='209.132.180.67', Host='vger.kernel.org', Country='US', FromHeader='com', MailFrom='org' X-Spam-charsets: plain='ascii' X-Resolved-to: greg@kroah.com X-Delivered-to: greg@kroah.com X-Mail-from: stable-owner@vger.kernel.org ARC-Seal: i=1; a=rsa-sha256; cv=none; d=messagingengine.com; s=arctest; t=1517970190; b=SaLs+oe4bczSccqJpGqEPmqfcaq0m6Qi/futl0urxWQpP1A +fndbx56Fyk4p68oxkXOLpz3DY9f12kBsQEH3LcBUBJwi5It/4wjf2pSklp2jlHf ruA2YidSwtoPWGMeTuJBSPSyOZbXzBRrT6VjnlEKIW8zqoezhHNv4xCe/p0crLtI P9EA5OHRfiDMobNIg/W9VV4IKvfkNMjwedM3L1CSVMGdHaIWsq3LYRe0tiGe+IU2 TOyTm9zMn3Qerq/D31S2QCi3Lkx/OI3LxNrr+LYQm+/C0o7/AQ5TmAPvnG0iCU3G oFOlL7+7KyzLD11KCCTJXGWmdnw2XW2Pwpb8rRw== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d= messagingengine.com; h=from:to:cc:subject:references:date :in-reply-to:message-id:mime-version:content-type:sender :list-id; s=arctest; t=1517970190; bh=mI06S9mZAS+q9cfNaNP2tlAjck uBIJsnz2lIyo4BwPc=; b=HBiInIk3bxZiDt5rV5bwiQOEnk4rP/l0KvBlnifB53 HpJZ88kq66mAXsKj32kL09e9PXIyK0h5Fw+fXa41+6xviDuAjjGWQ2ROY0xTzMN2 mM+3lm0Dga4I5jxovVBJelHZkBZ8NYP0zniInXLed/ZtGtEquZuX0DHQ/6ACuuQg hZY5Cts50WusylpFOpQJFAt3ljS4R27s1FAWckzRa6g8IlHTtyFSoiK9//hL6X/l Vq30ySBDTsNccDIN3yaXvyu/cKiv7g9juuf+Bk8mO+hOUySSOdYeTqPI+xKG9BhW yQ9Ms+COjFTqFbpZHHFtdyNoVk4Cg4fVlc+8HWuorHEQ== ARC-Authentication-Results: i=1; mx3.messagingengine.com; arc=none (no signatures found); dkim=none (no signatures found); dmarc=none (p=none,has-list-id=yes,d=none) header.from=intel.com; iprev=pass policy.iprev=209.132.180.67 (vger.kernel.org); spf=none smtp.mailfrom=stable-owner@vger.kernel.org smtp.helo=vger.kernel.org; x-aligned-from=fail; x-ptr=pass x-ptr-helo=vger.kernel.org x-ptr-lookup=vger.kernel.org; x-return-mx=pass smtp.domain=vger.kernel.org smtp.result=pass smtp_org.domain=kernel.org smtp_org.result=pass smtp_is_org_domain=no header.domain=intel.com header.result=pass header_is_org_domain=yes Authentication-Results: mx3.messagingengine.com; arc=none (no signatures found); dkim=none (no signatures found); dmarc=none (p=none,has-list-id=yes,d=none) header.from=intel.com; iprev=pass policy.iprev=209.132.180.67 (vger.kernel.org); spf=none smtp.mailfrom=stable-owner@vger.kernel.org smtp.helo=vger.kernel.org; x-aligned-from=fail; x-ptr=pass x-ptr-helo=vger.kernel.org x-ptr-lookup=vger.kernel.org; x-return-mx=pass smtp.domain=vger.kernel.org smtp.result=pass smtp_org.domain=kernel.org smtp_org.result=pass smtp_is_org_domain=no header.domain=intel.com header.result=pass header_is_org_domain=yes Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752738AbeBGCXH (ORCPT ); Tue, 6 Feb 2018 21:23:07 -0500 Received: from mga01.intel.com ([192.55.52.88]:23655 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751558AbeBGCXH (ORCPT ); Tue, 6 Feb 2018 21:23:07 -0500 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.46,471,1511856000"; d="scan'208";a="16104425" From: "Huang\, Ying" To: Minchan Kim Cc: huang ying , Andrew Morton , , LKML , Konrad Rzeszutek Wilk , Dan Streetman , Seth Jennings , Tetsuo Handa , Shaohua Li , Michal Hocko , Johannes Weiner , Mel Gorman , Shakeel Butt , , Sergey Senozhatsky Subject: Re: [PATCH -mm] mm, swap, frontswap: Fix THP swap if frontswap enabled References: <20180206065404.18815-1-ying.huang@intel.com> <20180206083101.GA17082@eng-minchan1.roam.corp.google.com> <871shy3421.fsf@yhuang-dev.intel.com> <20180206090244.GA20545@eng-minchan1.roam.corp.google.com> <20180206143505.GB25912@eng-minchan1.roam.corp.google.com> Date: Wed, 07 Feb 2018 10:23:03 +0800 In-Reply-To: <20180206143505.GB25912@eng-minchan1.roam.corp.google.com> (Minchan Kim's message of "Tue, 6 Feb 2018 06:35:05 -0800") Message-ID: <87fu6d1qt4.fsf@yhuang-dev.intel.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/25.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=ascii Sender: stable-owner@vger.kernel.org X-Mailing-List: stable@vger.kernel.org X-getmail-retrieved-from-mailbox: INBOX X-Mailing-List: linux-kernel@vger.kernel.org List-ID: Minchan Kim writes: > On Tue, Feb 06, 2018 at 09:34:44PM +0800, huang ying wrote: >> On Tue, Feb 6, 2018 at 5:02 PM, Minchan Kim wrote: >> > On Tue, Feb 06, 2018 at 04:39:18PM +0800, Huang, Ying wrote: >> >> Hi, Minchan, >> >> >> >> Minchan Kim writes: >> >> >> >> > Hi Huang, >> >> > >> >> > On Tue, Feb 06, 2018 at 02:54:04PM +0800, Huang, Ying wrote: >> >> >> From: Huang Ying >> >> >> >> >> >> It was reported by Sergey Senozhatsky that if THP (Transparent Huge >> >> >> Page) and frontswap (via zswap) are both enabled, when memory goes low >> >> >> so that swap is triggered, segfault and memory corruption will occur >> >> >> in random user space applications as follow, >> >> >> >> >> >> kernel: urxvt[338]: segfault at 20 ip 00007fc08889ae0d sp 00007ffc73a7fc40 error 6 in libc-2.26.so[7fc08881a000+1ae000] >> >> >> #0 0x00007fc08889ae0d _int_malloc (libc.so.6) >> >> >> #1 0x00007fc08889c2f3 malloc (libc.so.6) >> >> >> #2 0x0000560e6004bff7 _Z14rxvt_wcstoutf8PKwi (urxvt) >> >> >> #3 0x0000560e6005e75c n/a (urxvt) >> >> >> #4 0x0000560e6007d9f1 _ZN16rxvt_perl_interp6invokeEP9rxvt_term9hook_typez (urxvt) >> >> >> #5 0x0000560e6003d988 _ZN9rxvt_term9cmd_parseEv (urxvt) >> >> >> #6 0x0000560e60042804 _ZN9rxvt_term6pty_cbERN2ev2ioEi (urxvt) >> >> >> #7 0x0000560e6005c10f _Z17ev_invoke_pendingv (urxvt) >> >> >> #8 0x0000560e6005cb55 ev_run (urxvt) >> >> >> #9 0x0000560e6003b9b9 main (urxvt) >> >> >> #10 0x00007fc08883af4a __libc_start_main (libc.so.6) >> >> >> #11 0x0000560e6003f9da _start (urxvt) >> >> >> >> >> >> After bisection, it was found the first bad commit is >> >> >> bd4c82c22c367e068 ("mm, THP, swap: delay splitting THP after swapped >> >> >> out"). >> >> >> >> >> >> The root cause is as follow. >> >> >> >> >> >> When the pages are written to storage device during swapping out in >> >> >> swap_writepage(), zswap (fontswap) is tried to compress the pages >> >> >> instead to improve the performance. But zswap (frontswap) will treat >> >> >> THP as normal page, so only the head page is saved. After swapping >> >> >> in, tail pages will not be restored to its original contents, so cause >> >> >> the memory corruption in the applications. >> >> >> >> >> >> This is fixed via splitting THP at the begin of swapping out if >> >> >> frontswap is enabled. To avoid frontswap to be enabled at runtime, >> >> >> whether the page is THP is checked before using frontswap during >> >> >> swapping out too. >> >> > >> >> > Nice catch, Huang. However, before the adding a new dependency between >> >> > frontswap and vmscan that I want to avoid if it is possible, let's think >> >> > whether frontswap can support THP page or not. >> >> > Can't we handle it with some loop to handle all of subpages of THP page? >> >> > It might be not hard? >> >> >> >> Yes. That could be an optimization over this patch. This patch is just >> >> a simple fix to make things work and be suitable for stable tree. >> > >> > Yub, it would be more complex than this patch. However, this patch introduces >> > a new dependency to vmscan.c. IOW, we have been good without knowing frontswap >> > in vmscan.c but from now on, we should be aware of that, which is unfortunate. >> > >> > Can't we simple do like that if you want to make it simple and rely on someone >> > who makes frontswap THP-aware later? >> > >> > diff --git a/mm/swapfile.c b/mm/swapfile.c >> > index 42fe5653814a..4bf1725407aa 100644 >> > --- a/mm/swapfile.c >> > +++ b/mm/swapfile.c >> > @@ -934,7 +934,11 @@ int get_swap_pages(int n_goal, bool cluster, swp_entry_t swp_entries[]) >> > >> > /* Only single cluster request supported */ >> > WARN_ON_ONCE(n_goal > 1 && cluster); >> > +#ifdef CONFIG_FRONTSWAP >> > + /* Now, frontswap doesn't support THP page */ >> > + if (frontswap_enabled() && cluster) >> > + return; >> > +#endif >> > avail_pgs = atomic_long_read(&nr_swap_pages) / nr_pages; >> > if (avail_pgs <= 0) >> > goto noswap; >> > >> >> This can avoid introduce dependency on frontswap in vmscan.c. But >> IMHO it doesn't look like the right place to place the logic. >> vmscan.c is the place we put policy to determine whether to split THP. > > It adds split policy in vmscan.c like you said. > > shrink_page_list already relies on swap_file.c to decide split a THP page. > IOW, if a THP swap stuff is not avilable, split a thp. > It's totally same logic. I don't see any difference at all. > > shrink_page_list: > > if (!add_to_swap(page)) { > if (PageTransHuge(page)) > goto activate_locked; > if (split_huge_page_to_list(page, page_list)) > goto activate_locked; > count_vm_event(THP_SWPOUT_FALLBACK); > if (!add_to_swap(page)) > goto activate_locked; > } OK. I will change the code as you suggested. Best Regards, Huang, Ying