From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qt0-f197.google.com (mail-qt0-f197.google.com [209.85.216.197]) by kanga.kvack.org (Postfix) with ESMTP id DF0386B0260 for ; Mon, 12 Feb 2018 11:26:09 -0500 (EST) Received: by mail-qt0-f197.google.com with SMTP id f21so102335qtm.11 for ; Mon, 12 Feb 2018 08:26:09 -0800 (PST) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id v67sor2291919qki.4.2018.02.12.08.26.08 for (Google Transport Security); Mon, 12 Feb 2018 08:26:08 -0800 (PST) Date: Mon, 12 Feb 2018 11:26:06 -0500 (EST) From: Dan Streetman Subject: Re: [PATCH -mm -v2] mm, swap, frontswap: Fix THP swap if frontswap enabled In-Reply-To: <20180208173734.GA80964@eng-minchan1.roam.corp.google.com> Message-ID: References: <20180207070035.30302-1-ying.huang@intel.com> <20180208173734.GA80964@eng-minchan1.roam.corp.google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Sender: owner-linux-mm@kvack.org List-ID: To: Minchan Kim Cc: huang ying , Konrad Rzeszutek Wilk , Andrew Morton , linux-mm@kvack.org, LKML , Seth Jennings , Tetsuo Handa , Shaohua Li , Michal Hocko , Johannes Weiner , Mel Gorman , Shakeel Butt , stable@vger.kernel.org, Sergey Senozhatsky , "Huang, Ying" On Thu, 8 Feb 2018, Minchan Kim wrote: > Hi Huang, > > On Thu, Feb 08, 2018 at 11:27:50PM +0800, huang ying wrote: > > On Wed, Feb 7, 2018 at 3:00 PM, 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 swap 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 before writing the page to swap device > > > if frontswap is enabled. To deal with the situation where frontswap > > > is enabled at runtime, whether the page is THP is checked before using > > > frontswap during swapping out too. > > > > > > Reported-and-tested-by: Sergey Senozhatsky > > > Signed-off-by: "Huang, Ying" > > > Cc: Konrad Rzeszutek Wilk > > > Cc: Dan Streetman > > > Cc: Seth Jennings > > > Cc: Minchan Kim > > > Cc: Tetsuo Handa > > > Cc: Shaohua Li > > > Cc: Michal Hocko > > > Cc: Johannes Weiner > > > Cc: Mel Gorman > > > Cc: Shakeel Butt > > > Cc: stable@vger.kernel.org # 4.14 > > > Fixes: bd4c82c22c367e068 ("mm, THP, swap: delay splitting THP after swapped out") > > > > > > Changelog: > > > > > > v2: > > > > > > - Move frontswap check into swapfile.c to avoid to make vmscan.c > > > depends on frontswap. > > > --- > > > mm/page_io.c | 2 +- > > > mm/swapfile.c | 3 +++ > > > 2 files changed, 4 insertions(+), 1 deletion(-) > > > > > > diff --git a/mm/page_io.c b/mm/page_io.c > > > index b41cf9644585..6dca817ae7a0 100644 > > > --- a/mm/page_io.c > > > +++ b/mm/page_io.c > > > @@ -250,7 +250,7 @@ int swap_writepage(struct page *page, struct writeback_control *wbc) > > > unlock_page(page); > > > goto out; > > > } > > > - if (frontswap_store(page) == 0) { > > > + if (!PageTransHuge(page) && frontswap_store(page) == 0) { > > > set_page_writeback(page); > > > unlock_page(page); > > > end_page_writeback(page); > > > diff --git a/mm/swapfile.c b/mm/swapfile.c > > > index 006047b16814..0b7c7883ce64 100644 > > > --- a/mm/swapfile.c > > > +++ b/mm/swapfile.c > > > @@ -934,6 +934,9 @@ 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); > > > + /* Frontswap doesn't support THP */ > > > + if (frontswap_enabled() && cluster) > > > + goto noswap; > > > > I found this will cause THP swap optimization be turned off forever if > > CONFIG_ZSWAP=y (which cannot =m). Because frontswap is enabled quite > > statically instead of dynamically. If frontswap_ops is registered, it > > will be enabled unconditionally and forever. And zswap will register > > frontswap_ops during initialize regardless whether zswap is enabled or > > not. > > Indeed. > > > > > So I think it will be better to remove swapfile.c changes in this > > patch, just keep page_io.c changes. Because THP is more dynamic, it > > Then, I think it should be done by frontswap backend rather than generic > swap layer. Because there are two backends now and one of them can support > first. I like this approach. It allows zswap or xen tmem to support THP in the future. > > diff --git a/drivers/xen/tmem.c b/drivers/xen/tmem.c > index bf13d1ec51f3..bdaf309aeea6 100644 > --- a/drivers/xen/tmem.c > +++ b/drivers/xen/tmem.c > @@ -284,6 +284,9 @@ static int tmem_frontswap_store(unsigned type, pgoff_t offset, > int pool = tmem_frontswap_poolid; > int ret; > > + if (PageTransHuge(page)) > + return -EINVAL; > + > if (pool < 0) > return -1; > if (ind64 != ind) > diff --git a/mm/zswap.c b/mm/zswap.c > index c004aa4fd3f4..e343534d2892 100644 > --- a/mm/zswap.c > +++ b/mm/zswap.c > @@ -1007,6 +1007,9 @@ static int zswap_frontswap_store(unsigned type, pgoff_t offset, > u8 *src, *dst; > struct zswap_header zhdr = { .swpentry = swp_entry(type, offset) }; > > + if (PageTransHuge(page)) > + return -EINVAL; > + > if (!zswap_enabled || !tree) { > ret = -ENODEV; > goto reject; > > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. 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