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Thu, 8 Feb 2018 19:39:14 -0500 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.46,481,1511856000"; d="scan'208";a="16351058" From: "Huang\, Ying" To: Minchan Kim Cc: huang ying , Konrad Rzeszutek Wilk , Andrew Morton , , LKML , Dan Streetman , "Seth Jennings" , Tetsuo Handa , Shaohua Li , "Michal Hocko" , Johannes Weiner , Mel Gorman , Shakeel Butt , , Sergey Senozhatsky Subject: Re: [PATCH -mm -v2] mm, swap, frontswap: Fix THP swap if frontswap enabled References: <20180207070035.30302-1-ying.huang@intel.com> <20180208173734.GA80964@eng-minchan1.roam.corp.google.com> Date: Fri, 09 Feb 2018 08:39:10 +0800 In-Reply-To: <20180208173734.GA80964@eng-minchan1.roam.corp.google.com> (Minchan Kim's message of "Thu, 8 Feb 2018 09:37:35 -0800") Message-ID: <87a7wjyp1t.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: > 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. > > 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; Good suggestion! I will do this. Best Regards, Huang, Ying