From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lf0-f70.google.com (mail-lf0-f70.google.com [209.85.215.70]) by kanga.kvack.org (Postfix) with ESMTP id 2072D6B0038 for ; Wed, 20 Dec 2017 16:20:49 -0500 (EST) Received: by mail-lf0-f70.google.com with SMTP id n199so5459610lfb.21 for ; Wed, 20 Dec 2017 13:20:49 -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 c4sor3236452ljd.63.2017.12.20.13.20.47 for (Google Transport Security); Wed, 20 Dec 2017 13:20:47 -0800 (PST) Subject: Re: [PATCH v2] mm/zsmalloc: simplify shrinker init/destroy References: <20171219152536.GA591@tigerII.localdomain> <20171219155815.GC2787@dhcp22.suse.cz> <20171220071500.GA11774@jagdpanzerIV> <04faff62-0944-3c7d-15b0-9dc60054a830@gmail.com> <20171220083403.GC11774@jagdpanzerIV> <20171220090828.GB4831@dhcp22.suse.cz> <20171220091653.GE11774@jagdpanzerIV> <20171220092513.GF4831@dhcp22.suse.cz> <20171220113835.GO4831@dhcp22.suse.cz> <20171220115751.GP4831@dhcp22.suse.cz> From: Aliaksei Karaliou Message-ID: Date: Thu, 21 Dec 2017 00:20:44 +0300 MIME-Version: 1.0 In-Reply-To: <20171220115751.GP4831@dhcp22.suse.cz> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko , Tetsuo Handa Cc: Sergey Senozhatsky , Andrew Morton , Sergey Senozhatsky , minchan@kernel.org, ngupta@vflare.org, linux-mm@kvack.org On 12/20/2017 02:57 PM, Michal Hocko wrote: > On Wed 20-12-17 12:38:35, Michal Hocko wrote: >> On Wed 20-12-17 20:05:35, Tetsuo Handa wrote: >>> On 2017/12/20 18:25, Michal Hocko wrote: >>>> On Wed 20-12-17 18:16:53, Sergey Senozhatsky wrote: >>>>> On (12/20/17 10:08), Michal Hocko wrote: >>>>> [..] >>>>>>> let's keep void zs_register_shrinker() and just suppress the >>>>>>> register_shrinker() must_check warning. >>>>>> I would just hope we simply drop the must_check nonsense. >>>>> agreed. given that unregister_shrinker() does not oops anymore, >>>>> enforcing that check does not make that much sense. >>>> Well, the registration failure is a failure like any others. Ignoring >>>> the failure can have bad influence on the overal system behavior but >>>> that is no different from thousands of other functions. must_check is an >>>> overreaction here IMHO. >>>> >>> I don't think that must_check is an overreaction. >>> As of linux-next-20171218, no patch is available for 10 locations. >>> >>> drivers/staging/android/ion/ion_heap.c:306: register_shrinker(&heap->shrinker); >>> drivers/staging/android/ashmem.c:857: register_shrinker(&ashmem_shrinker); >>> drivers/gpu/drm/ttm/ttm_page_alloc_dma.c:1185: register_shrinker(&manager->mm_shrink); >>> drivers/gpu/drm/ttm/ttm_page_alloc.c:484: register_shrinker(&manager->mm_shrink); >>> drivers/gpu/drm/i915/i915_gem_shrinker.c:508: WARN_ON(register_shrinker(&i915->mm.shrinker)); >>> drivers/gpu/drm/msm/msm_gem_shrinker.c:154: WARN_ON(register_shrinker(&priv->shrinker)); >>> drivers/md/dm-bufio.c:1756: register_shrinker(&c->shrinker); >>> drivers/android/binder_alloc.c:1012: register_shrinker(&binder_shrinker); >>> arch/x86/kvm/mmu.c:5485: register_shrinker(&mmu_shrinker); >>> fs/xfs/xfs_qm.c:698: register_shrinker(&qinf->qi_shrinker); >> And how exactly has the must_check helped for those? Come on, start >> being serious finally. This is a matter of fixing those. You have done >> a good deal of work for some, it just takes to finish the rest. The >> warning doesn't help on its own, it just makes people ignore it after >> some time or make it silent in some way. > Also have a look at how WARN_ON simply papers over the wrong code and > must_check will not help you the slightest. Regarding the other locations where return code is ignored, I think I will try to fix them as I did in Lustre code recently. However, it might be not straightforward and zsmalloc is good example - we understand that failure is not critical and we can live without shrinker. Locations specified by Michal are also different, for example: drivers/gpu/drm/i915/i915_gem_shrinker.c:508: WARN_ON(register_shrinker(&i915->mm.shrinker)); - this change is intentional. arch/x86/kvm/mmu.c:5485: register_shrinker(&mmu_shrinker); - was made before register_shrinker() became non-void. and so on. The question is what to do in each particular case ? Some people may consider wrapping it with WARN_ON to be rather good option too while the others will prefer to consider it as a critical failure or at least do their own logging, with still looks similar with WARN_ON for me imho. For me, must_check looks like thing that works mostly for new code only, but in this case it works like a trigger that forces people to act and fix previously written code, but yes, all depends on attitude as Michal noticed. Best regards, Aliaksei. -- 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