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Patch series "cleanup zonelists initialization", v1. This is aimed at cleaning up the zonelists initialization code we have but the primary motivation was bug report [2] which got resolved but the usage of stop_machine is just too ugly to live. Most patches are straightforward but 3 of them need a special consideration. Patch 1 removes zone ordered zonelists completely. I am CCing linux-api because this is a user visible change. As I argue in the patch description I do not think we have a strong usecase for it these days. I have kept sysctl in place and warn into the log if somebody tries to configure zone lists ordering. If somebody has a real usecase for it we can revert this patch but I do not expect anybody will actually notice runtime differences. This patch is not strictly needed for the rest but it made patch 6 easier to implement. Patch 7 removes stop_machine from build_all_zonelists without adding any special synchronization between iterators and updater which I _believe_ is acceptable as explained in the changelog. I hope I am not missing anything. Patch 8 then removes zonelists_mutex which is kind of ugly as well and not really needed AFAICS but a care should be taken when double checking my thinking. This patch (of 9): Supporting zone ordered zonelists costs us just a lot of code while the usefulness is arguable if existent at all. Mel has already made node ordering default on 64b systems. 32b systems are still using ZONELIST_ORDER_ZONE because it is considered better to fallback to a different NUMA node rather than consume precious lowmem zones. This argument is, however, weaken by the fact that the memory reclaim has been reworked to be node rather than zone oriented. This means that lowmem requests have to skip over all highmem pages on LRUs already and so zone ordering doesn't save the reclaim time much. So the only advantage of the zone ordering is under a light memory pressure when highmem requests do not ever hit into lowmem zones and the lowmem pressure doesn't need to reclaim. Considering that 32b NUMA systems are rather suboptimal already and it is generally advisable to use 64b kernel on such a HW I believe we should rather care about the code maintainability and just get rid of ZONELIST_ORDER_ZONE altogether. Keep systcl in place and warn if somebody tries to set zone ordering either from kernel command line or the sysctl. [mhocko@suse.com: reading vm.numa_zonelist_order will never terminate] Link: http://lkml.kernel.org/r/20170721143915.14161-2-mhocko@kernel.org Signed-off-by: Michal Hocko <mhocko@suse.com> Acked-by: Mel Gorman <mgorman@suse.de> Acked-by: Vlastimil Babka <vbabka@suse.cz> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Joonsoo Kim <js1304@gmail.com> Cc: Shaohua Li <shaohua.li@intel.com> Cc: Toshi Kani <toshi.kani@hpe.com> Cc: Abdul Haleem <abdhalee@linux.vnet.ibm.com> Cc: <linux-api@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> |
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Documentation for /proc/sys/ kernel version 2.2.10 (c) 1998, 1999, Rik van Riel <riel@nl.linux.org> 'Why', I hear you ask, 'would anyone even _want_ documentation for them sysctl files? If anybody really needs it, it's all in the source...' Well, this documentation is written because some people either don't know they need to tweak something, or because they don't have the time or knowledge to read the source code. Furthermore, the programmers who built sysctl have built it to be actually used, not just for the fun of programming it :-) ============================================================== Legal blurb: As usual, there are two main things to consider: 1. you get what you pay for 2. it's free The consequences are that I won't guarantee the correctness of this document, and if you come to me complaining about how you screwed up your system because of wrong documentation, I won't feel sorry for you. I might even laugh at you... But of course, if you _do_ manage to screw up your system using only the sysctl options used in this file, I'd like to hear of it. Not only to have a great laugh, but also to make sure that you're the last RTFMing person to screw up. In short, e-mail your suggestions, corrections and / or horror stories to: <riel@nl.linux.org> Rik van Riel. ============================================================== Introduction: Sysctl is a means of configuring certain aspects of the kernel at run-time, and the /proc/sys/ directory is there so that you don't even need special tools to do it! In fact, there are only four things needed to use these config facilities: - a running Linux system - root access - common sense (this is especially hard to come by these days) - knowledge of what all those values mean As a quick 'ls /proc/sys' will show, the directory consists of several (arch-dependent?) subdirs. Each subdir is mainly about one part of the kernel, so you can do configuration on a piece by piece basis, or just some 'thematic frobbing'. The subdirs are about: abi/ execution domains & personalities debug/ <empty> dev/ device specific information (eg dev/cdrom/info) fs/ specific filesystems filehandle, inode, dentry and quota tuning binfmt_misc <Documentation/binfmt_misc.txt> kernel/ global kernel info / tuning miscellaneous stuff net/ networking stuff, for documentation look in: <Documentation/networking/> proc/ <empty> sunrpc/ SUN Remote Procedure Call (NFS) vm/ memory management tuning buffer and cache management user/ Per user per user namespace limits These are the subdirs I have on my system. There might be more or other subdirs in another setup. If you see another dir, I'd really like to hear about it :-)