From: Michal Hocko <mhocko@kernel.org> To: Johannes Weiner <hannes@cmpxchg.org> Cc: Dave Gordon <david.s.gordon@intel.com>, linux-mm@kvack.org, intel-gfx@lists.freedesktop.org, "Goel, Akash" <akash.goel@intel.com> Subject: Re: [Intel-gfx] [PATCH v2 1/2] mm: Export nr_swap_pages Date: Tue, 8 Dec 2015 12:22:25 +0100 [thread overview] Message-ID: <20151208112225.GB25800@dhcp22.suse.cz> (raw) In-Reply-To: <20151207191346.GA3872@cmpxchg.org> On Mon 07-12-15 14:13:46, Johannes Weiner wrote: > On Mon, Dec 07, 2015 at 06:10:00PM +0000, Dave Gordon wrote: > > Exporting random uncontrolled variables from the kernel to loaded modules is > > not really considered best practice. It would be preferable to provide an > > accessor function - which is just what the declaration says we have; the > > implementation as a static inline (and/or macro) is what causes the problem > > here. > > No, what causes the problem is thinking we can't trust in-kernel code. This is not about the trust. It is about a clear API and separation. > If somebody screws up, we can fix it easily enough. Sure, we shouldn't > be laying traps and create easy-to-misuse interfaces, but that's not > what's happening here. There is no reason to add function overhead to > what should be a single 'mov' instruction. The mere fact that the current implementation is a simple atomic_long_read is a detail and not important for the API. The function is not used in any hot path where a single function call overhead would be a performance killer. Exporting implementation details to random users tends to add maintenance burden in future. I think it is natural to export symbols which are consumed by modules and that will be get_nr_swap_pages(). I do not even understand the resistance against that. Anyway I am not going to argue about it more. I have raised my review comment and leave the decision to Chris/Andrew. -- Michal Hocko SUSE Labs -- 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: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
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From: Michal Hocko <mhocko@kernel.org> To: Johannes Weiner <hannes@cmpxchg.org> Cc: intel-gfx@lists.freedesktop.org, "Goel, Akash" <akash.goel@intel.com>, linux-mm@kvack.org Subject: Re: [PATCH v2 1/2] mm: Export nr_swap_pages Date: Tue, 8 Dec 2015 12:22:25 +0100 [thread overview] Message-ID: <20151208112225.GB25800@dhcp22.suse.cz> (raw) In-Reply-To: <20151207191346.GA3872@cmpxchg.org> On Mon 07-12-15 14:13:46, Johannes Weiner wrote: > On Mon, Dec 07, 2015 at 06:10:00PM +0000, Dave Gordon wrote: > > Exporting random uncontrolled variables from the kernel to loaded modules is > > not really considered best practice. It would be preferable to provide an > > accessor function - which is just what the declaration says we have; the > > implementation as a static inline (and/or macro) is what causes the problem > > here. > > No, what causes the problem is thinking we can't trust in-kernel code. This is not about the trust. It is about a clear API and separation. > If somebody screws up, we can fix it easily enough. Sure, we shouldn't > be laying traps and create easy-to-misuse interfaces, but that's not > what's happening here. There is no reason to add function overhead to > what should be a single 'mov' instruction. The mere fact that the current implementation is a simple atomic_long_read is a detail and not important for the API. The function is not used in any hot path where a single function call overhead would be a performance killer. Exporting implementation details to random users tends to add maintenance burden in future. I think it is natural to export symbols which are consumed by modules and that will be get_nr_swap_pages(). I do not even understand the resistance against that. Anyway I am not going to argue about it more. I have raised my review comment and leave the decision to Chris/Andrew. -- Michal Hocko SUSE Labs _______________________________________________ Intel-gfx mailing list Intel-gfx@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/intel-gfx
next prev parent reply other threads:[~2015-12-08 11:22 UTC|newest] Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top 2015-12-04 15:58 [PATCH v2 1/2] mm: Export nr_swap_pages Chris Wilson 2015-12-04 15:58 ` [PATCH v2 2/2] drm/i915: Disable shrinker for non-swapped backed objects Chris Wilson 2015-12-04 15:58 ` Chris Wilson 2015-12-04 16:11 ` Johannes Weiner 2015-12-04 16:11 ` Johannes Weiner 2015-12-10 9:34 ` Daniel Vetter 2015-12-04 16:09 ` [PATCH v2 1/2] mm: Export nr_swap_pages Johannes Weiner 2015-12-04 16:09 ` Johannes Weiner 2015-12-10 9:32 ` [Intel-gfx] " Daniel Vetter 2015-12-23 22:04 ` Johannes Weiner 2015-12-23 22:04 ` Johannes Weiner 2015-12-23 22:26 ` [Intel-gfx] " Andrew Morton 2016-01-05 10:05 ` Daniel Vetter 2015-12-07 13:48 ` Michal Hocko 2015-12-07 16:48 ` Johannes Weiner 2015-12-07 16:48 ` Johannes Weiner 2015-12-07 17:04 ` Michal Hocko 2015-12-07 18:02 ` Johannes Weiner 2015-12-07 18:02 ` Johannes Weiner 2015-12-07 18:10 ` [Intel-gfx] " Dave Gordon 2015-12-07 19:13 ` Johannes Weiner 2015-12-08 11:19 ` Dave Gordon 2015-12-08 11:19 ` Dave Gordon 2015-12-08 11:22 ` Michal Hocko [this message] 2015-12-08 11:22 ` Michal Hocko 2015-12-17 18:15 ` [PATCH v3] mm: Export {__}get_nr_swap_pages() Dave Gordon 2015-12-17 18:15 ` Dave Gordon 2015-12-17 19:45 ` Johannes Weiner 2015-12-17 19:45 ` Johannes Weiner
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