From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf1-f197.google.com (mail-pf1-f197.google.com [209.85.210.197]) by kanga.kvack.org (Postfix) with ESMTP id 7287C8E0001 for ; Fri, 28 Sep 2018 20:50:34 -0400 (EDT) Received: by mail-pf1-f197.google.com with SMTP id y8-v6so7113689pfl.11 for ; Fri, 28 Sep 2018 17:50:34 -0700 (PDT) Received: from mga02.intel.com (mga02.intel.com. [134.134.136.20]) by mx.google.com with ESMTPS id s16-v6si6029820pgg.19.2018.09.28.17.50.32 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 28 Sep 2018 17:50:33 -0700 (PDT) From: "Huang\, Ying" Subject: Re: [PATCH -V5 RESEND 03/21] swap: Support PMD swap mapping in swap_duplicate() References: <20180925071348.31458-1-ying.huang@intel.com> <20180925071348.31458-4-ying.huang@intel.com> <20180925191953.4ped5ki7u3ymafmd@ca-dmjordan1.us.oracle.com> <874lecifj4.fsf@yhuang-dev.intel.com> <20180926145145.6xp2kxpngyd54f6i@ca-dmjordan1.us.oracle.com> <87r2hfhger.fsf@yhuang-dev.intel.com> <20180927211238.ly3e7cyvfu3rswcv@ca-dmjordan1.us.oracle.com> <87lg7mf30o.fsf@yhuang-dev.intel.com> <20180928213224.tjff2rtfmxmnz5nq@ca-dmjordan1.us.oracle.com> Date: Sat, 29 Sep 2018 08:50:29 +0800 In-Reply-To: <20180928213224.tjff2rtfmxmnz5nq@ca-dmjordan1.us.oracle.com> (Daniel Jordan's message of "Fri, 28 Sep 2018 14:32:24 -0700") Message-ID: <877ej5f7oq.fsf@yhuang-dev.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=ascii Sender: owner-linux-mm@kvack.org List-ID: To: Daniel Jordan Cc: Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, "Kirill A. Shutemov" , Andrea Arcangeli , Michal Hocko , Johannes Weiner , Shaohua Li , Hugh Dickins , Minchan Kim , Rik van Riel , Dave Hansen , Naoya Horiguchi , Zi Yan Daniel Jordan writes: > On Fri, Sep 28, 2018 at 04:19:03PM +0800, Huang, Ying wrote: >> Daniel Jordan writes: >> > One way is to change >> > copy_one_pte's return to int so we can just pass the error code back to >> > copy_pte_range so it knows whether to try adding the continuation. >> >> There may be even more problems. After add_swap_count_continuation(), >> copy_one_pte() will be retried, and the CPU may hang with dead loop. > > That's true, it would do that. > >> But before the changes in this patchset, the behavior is, >> __swap_duplicate() return an error that isn't -ENOMEM, such as -EEXIST. >> Then copy_one_pte() would thought the operation has been done >> successfully, and go to call set_pte_at(). This will cause the system >> state become inconsistent, and the system may panic or hang somewhere >> later. >> >> So per my understanding, if we thought page table corruption isn't a >> real problem (that is, __swap_duplicate() will never return e.g. -EEXIST >> if copied by copy_one_pte() indirectly), both the original and the new >> code should be OK. >> >> If we thought it is a real problem, we need to fix the original code and >> keep it fixed in the new code. Do you agree? > > Yes, if it was a real problem, which seems less and less the case the more I > stare at this. > >> There's several ways to fix the problem. But the page table shouldn't >> be corrupted in practice, unless there's some programming error. So I >> suggest to make it as simple as possible via adding, >> >> VM_BUG_ON(error != -ENOMEM); >> >> in swap_duplicate(). >> >> Do you agree? > > Yes, I'm ok with that, adding in -ENOTDIR along with it. Sure. I will do this. > The error handling in __swap_duplicate (before this series) still leaves > something to be desired IMHO. Why all the different returns when callers > ignore them or only specifically check for -ENOMEM or -EEXIST? Could maybe > stand a cleanup, but outside this series. Yes. Maybe. I guess you will work on this? Best Regards, Huang, Ying