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It turns out that it is advantageous to leave a small portion of unmapped file backed pages if all of a zone's pages (or almost all pages) are allocated and so the page allocator has to go off-node. This allows recently used file I/O buffers to stay on the node and reduces the times that zone reclaim is invoked if file I/O occurs when we run out of memory in a zone. The problem is that zone reclaim runs too frequently when the page cache is used for file I/O (read write and therefore unmapped pages!) alone and we have almost all pages of the zone allocated. Zone reclaim may remove 32 unmapped pages. File I/O will use these pages for the next read/write requests and the unmapped pages increase. After the zone has filled up again zone reclaim will remove it again after only 32 pages. This cycle is too inefficient and there are potentially too many zone reclaim cycles. With the 1% boundary we may still remove all unmapped pages for file I/O in zone reclaim pass. However. it will take a large number of read and writes to get back to 1% again where we trigger zone reclaim again. The zone reclaim 2.6.16/17 does not show this behavior because we have a 30 second timeout. [akpm@osdl.org: rename the /proc file and the variable] Signed-off-by: Christoph Lameter <clameter@sgi.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.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 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 :-)